diff --git a/docs/mte.md b/docs/mte.md
new file mode 100644
index 0000000..3890283
--- /dev/null
+++ b/docs/mte.md
@@ -0,0 +1,244 @@
+# Arm Memory Tagging Extension (MTE) implementation
+
+AOSP supports Arm MTE to detect invalid memory accesses. The implementation is
+spread across multiple components, both within and out of the AOSP tree. This
+document gives an overview and pointers about how the various MTE features are
+implemented.
+
+For documentation of the behavior rather than the implementation, see the
+[SAC page on MTE] instead. For MTE for apps, see the [NDK page on MTE].
+
+The relevant components are:
+
+* [LLVM Project] (out of AOSP tree)
+    * Stack tagging instrumentation pass
+    * Scudo memory allocator
+* bionic
+    * libc
+    * dynamic loader
+* Zygote
+* debuggerd
+* [NDK]
+
+## MTE enablement
+
+The way MTE is requested and enabled differs between native binaries and Java
+apps. This is necessarily so, because Java apps get forked from the Zygote,
+while native executables get inintialized by the linker.
+
+### Native binaries
+
+Both AOSP and the NDK allow you to compile C/C++ code that use MTE to detect
+memory safety issues. The [NDK legacy cmake toolchain] and the
+[NDK new cmake toolchain] both support "memtag" as an argument for
+`ANDROID_SANITIZE`. NDK make has no specific support for MTE, but the
+relevant flags can be passed directly as `CFLAGS` and `LDFLAGS`.
+
+For the OS itself, [Soong] supports "memtag_[heap|stack|globals]" as
+`SANITIZE_TARGET  and as `sanitize:` attribute in Android.bp files;
+[Android make] supports the same environment variables as Soong. This passes
+the appropriate flags to the clang driver for both compile and link steps.
+
+#### Linker
+
+* For **dynamic executables** LLD has support to
+  [add appropriate dynamic sections] as defined in the [ELF standard]
+* For **static executables** and as a fallback for older devices, LLD
+  also supports [adding the Android-specific ELF note]
+
+Both of the above are controlled by the linker flag `--android-memtag-mode`
+which is [passed in by the clang driver] if
+`-fsanitize=memtag-[stack|heap|globals]` is [passed in].
+`-fsanitize=memtag` [enables all three] (even for API levels that don't
+implement the runtime for globals, which means builds from old versions
+of clang may no work with newer platform versions that support globals).
+`-fsanitize-memtag-mode` allows to choose between ASYNC and SYNC.
+
+This information can be queried using `llvm-readelf --memtag`.
+
+This information is [picked up by libc init] to decide whether to enable MTE.
+`-fsanitize-heap` controls both whether scudo tags allocations, and whether
+tag checking is enabled.
+
+#### Runtime environment (dynamic loader, libc)
+
+There are two different initialization sequences for libc, both of which end up
+calling `__libc_init_mte`.
+
+N.B. the linker has its own copy of libc, which is used when executing these
+functions. That is why we have to use `__libc_shared_globals` to communicate
+with the libc of the process we are starting.
+
+* **static executables** `__libc_init` is called from `crtbegin.c`, which calls
+                         `__libc_init_mte`
+* **dynamic executables** the linker calls `__libc_init_mte`
+
+`__libc_init_mte` figures out the appropriate MTE level that is requested by
+the process, calls `prctl` to request this from the kernel, and stores data in
+`__libc_shared_globals` which gets picked up later to enable MTE in scudo.
+
+It also does work related to stack tagging and permissive mode, which will be
+detailed later.
+
+### Apps
+
+Apps can request MTE be enabled for their process via the manifest attribute
+`android:memtagMode`. This gets interpreted by Zygote, which always runs with
+`ASYNC` MTE enabled, because MTE for a process can only be disabled after
+it has been initialized (see [Native binaries](#native-binaries)), not enabled.
+
+[decideTaggingLevel] in the Zygote figures out whether to enable MTE for
+an app, and stores it in the `runtimeFlags`, which get picked up by
+[SpecializeCommon] after forking from the Zygote.
+
+## MTE implementation
+
+### Heap Tagging
+
+Heap tagging is implemented in the scudo allocator. On `malloc` and `free`,
+scudo will update the memory's tags to prevent use-after-free and buffer
+overflows.
+
+[scudo's memtag.h] contains helper functions to deal with MTE tag management,
+which are used in [combined.h] and [secondary.h].
+
+
+### Stack Tagging
+
+Stack tagging requires instrumenting function bodies. It is implemented as
+an instrumentation pass in LLVM called [AArch64StackTagging], which sets
+the tags according to the lifetime of stack objects.
+
+The instrumentation pass also supports recording stack history, consisting of:
+
+* PC
+* Frame pointer
+* Base tag
+
+This can be used to reconstruct which stack object was referred to in an
+invalid access. The logic to reconstruct this can be found in the
+[stack script].
+
+
+Stack tagging is enabled in one of two circumstances:
+* at process startup, if the main binary or any of its dependencies are
+  compiled with `memtag-stack`
+* library compiled with `memtag-stack` is `dlopen`ed later, either directly or
+  as a dependency of a `dlopen`ed library. In this case, the
+  [__pthread_internal_remap_stack_with_mte] function is used (called from
+  `memtag_stack_dlopen_callback`). Because `dlopen`
+  is handled by the linker, we have to [store a function pointer] to the
+  process's version of the function in `__libc_shared_globals`.
+
+Enabling stack MTE consists of two operations:
+* Remapping the stacks as `PROT_MTE`
+* Allocating a stack history buffer.
+
+The first operation is only necessary when the process is running with MTE
+enabled. The second operation is also necessary when the process is not running
+with MTE enabled, because the writes to the stack history buffer are
+unconditional.
+
+libc keeps track of this through two globals:
+
+* `__libc_memtag_stack`:  whether stack MTE is enabled on the process, i.e.
+  whether the stack pages are mapped with PROT\_MTE. This is always false if
+  MTE is disabled for the process (i.e. `libc_globals.memtag` is false).
+* `__libc_memtag_stack_abi`: whether the process contains any code that was
+  compiled with memtag-stack. This is true even if the process does not have
+  MTE enabled.
+
+### Globals Tagging
+
+TODO(fmayer): write once submitted
+
+### Crash reporting
+
+For MTE crashes, debuggerd serializes special information into the Tombstone
+proto:
+
+* Tags around fault address
+* Scudo allocation history
+
+This is done in [tombstone\_proto.cpp]. The information is converted to a text
+proto in [tombstone\_proto\_to\_text.cpp].
+
+## Bootloader control
+
+The bootloader API allows userspace to enable MTE on devices that do not ship
+with MTE enabled by default.
+
+See [SAC bootloader support] for the API definition. In AOSP, this API is
+implemented in [system/extras/mtectrl]. mtectrl.rc handles the property
+changes and invokes mtectrl to update the misc partition to communicate
+with the bootloader.
+
+There is also an [API in Device Policy Manager] that allows the device admin
+to enable or disable MTE under certain circumstances.
+
+The device can opt in or out of these APIs by a set of system properties:
+
+* `ro.arm64.memtag.bootctl_supported`: the system property API is supported,
+  and an option is displayed in Developer Options.
+* `ro.arm64.memtag.bootctl_settings_toggle`: an option is displayed in the
+  normal settings. This requires `ro.arm64.memtag.bootctl_supported` to be
+  true. This implies `ro.arm64.memtag.bootctl_device_policy_manager`, if it
+  is not explicitely set.
+* `ro.arm64.memtag.bootctl_device_policy_manager`: the Device Policy Manager
+  API is supported.
+
+## Permissive MTE
+
+Permissive MTE refers to a mode which, instead of crashing the process on an
+MTE fault, records a tombstone but then continues execution of the process.
+An important caveat is that system calls with invalid pointers (where the
+pointer tag does not match the memory tag) still return an error code.
+
+This mode is only available for system services, not apps. It is implemented
+in the [debugger\_signal\_handler] by disabling MTE for the faulting thread.
+Optionally, the user can ask for MTE to be re-enabled after some time.
+This is achieved by arming a timer that calls [enable_mte_signal_handler]
+upon expiry.
+
+## MTE Mode Upgrade
+
+When a system service [crashes in ASYNC mode], we set an impossible signal
+as an exit code (because that signal is always gracefully handled by libc),
+and [in init] we set `BIONIC_MEMTAG_UPGRADE_SECS`, which gets handled by
+[libc startup].
+
+[SpecializeCommon]: https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/core/jni/com_android_internal_os_Zygote.cpp?q=f:frameworks%2Fbase%2Fcore%2Fjni%2Fcom_android_internal_os_Zygote.cpp%20%22%20mallopt(M_BIONIC_SET_HEAP_TAGGING_LEVEL,%22&ss=android%2Fplatform%2Fsuperproject%2Fmain
+[LLVM Project]: https://github.com/llvm/llvm-project/
+[NDK]: https://android.googlesource.com/platform/ndk/
+[NDK legacy cmake toolchain]: https://android.googlesource.com/platform/ndk/+/refs/heads/main/build/cmake/android-legacy.toolchain.cmake#490
+[NDK new cmake toolchain]: https://android.googlesource.com/platform/ndk/+/refs/heads/main/build/cmake/flags.cmake#56
+[Soong]: https://cs.android.com/android/platform/superproject/main/+/main:build/soong/cc/sanitize.go?q=sanitize.go&ss=android%2Fplatform%2Fsuperproject%2Fmain
+[decideTaggingLevel]: https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/core/java/com/android/internal/os/Zygote.java?q=symbol:decideTaggingLevel
+[picked up by libc init]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/bionic/libc_init_static.cpp?q=symbol:__get_tagging_level%20f:bionic
+[enables all three]: https://github.com/llvm/llvm-project/blob/e732d1ce86783b1d7fe30645fcb30434109505b9/clang/include/clang/Basic/Sanitizers.def#L62
+[passed in]: https://github.com/llvm/llvm-project/blob/ff2e619dfcd77328812a42d2ba2b11c3ff96f410/clang/lib/Driver/SanitizerArgs.cpp#L719
+[passed in by the clang driver]: https://github.com/llvm/llvm-project/blob/ff2e619dfcd77328812a42d2ba2b11c3ff96f410/clang/lib/Driver/ToolChains/CommonArgs.cpp#L1595
+[adding the Android-specific ELF note]: https://github.com/llvm/llvm-project/blob/435cb0dc5eca08cdd8d9ed0d887fa1693cc2bf33/lld/ELF/Driver.cpp#L1258
+[ELF standard]: https://github.com/ARM-software/abi-aa/blob/main/memtagabielf64/memtagabielf64.rst#6dynamic-section
+[add appropriate dynamic sections]: https://github.com/llvm/llvm-project/blob/7022498ac2f236e411e8a0f9a48669e754000a4b/lld/ELF/SyntheticSections.cpp#L1473
+[storeTags]: https://cs.android.com/android/platform/superproject/main/+/main:external/scudo/standalone/memtag.h?q=f:scudo%20f:memtag.h%20function:storeTags
+[SAC page on MTE]: https://source.android.com/docs/security/test/memory-safety/arm-mte
+[NDK page on MTE]: https://developer.android.com/ndk/guides/arm-mte
+[AArch64StackTagging]: https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64StackTagging.cpp
+[scudo's memtag.h]: https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/scudo/standalone/memtag.h
+[combined.h]: https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/scudo/standalone/combined.h
+[secondary.h]: https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/scudo/standalone/secondary.h
+[__pthread_internal_remap_stack_with_mte]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/bionic/pthread_internal.cpp?q=__pthread_internal_remap_stack_with_mte
+[stack script]: https://cs.android.com/android/platform/superproject/main/+/main:development/scripts/stack?q=stack
+[Android make]: https://cs.android.com/android/platform/superproject/main/+/main:build/make/core/config_sanitizers.mk
+[store a function pointer]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/bionic/libc_init_dynamic.cpp;l=168?q=memtag_stack_dlopen_callback
+[tombstone\_proto.cpp]: https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/libdebuggerd/tombstone_proto.cpp?q=tombstone_proto.cpp
+[tombstone\_proto\_to\_text.cpp]: https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/libdebuggerd/tombstone_proto_to_text.cpp
+[SAC MTE bootloader support]: https://source.android.com/docs/security/test/memory-safety/bootloader-support
+[system/extras/mtectrl]: https://cs.android.com/android/platform/superproject/main/+/main:system/extras/mtectrl/
+[API in Device Policy Manager]: https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/core/java/android/app/admin/DevicePolicyManager.java?q=symbol:setMtePolicy%20f:DevicePolicyManager.java
+[debuggerd\_signal_handler]: https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/handler/debuggerd_handler.cpp?q=f:debuggerd_handler.cpp%20symbol:debuggerd_signal_handler
+[enable_mte_signal_handler]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/bionic/libc_init_static.cpp?q=symbol:__enable_mte_signal_handler
+[in init]: https://cs.android.com/android/platform/superproject/main/+/main:system/core/init/service.cpp?q=f:system%2Fcore%2Finit%2Fservice.cpp%20should_upgrade_mte
+[crashes in ASYNC mode]: https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/handler/debuggerd_handler.cpp;l=799?q=BIONIC_SIGNAL_ART_PROFILER
+[libc startup]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/bionic/libc_init_static.cpp?q=BIONIC_MEMTAG_UPGRADE_SECS
diff --git a/libc/Android.bp b/libc/Android.bp
index ae6df52..5ae8c4f 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -264,6 +264,7 @@
     name: "libc_init_static",
     defaults: ["libc_defaults"],
     srcs: [
+        "bionic/libc_init_mte.cpp",
         "bionic/libc_init_static.cpp",
         ":elf_note_sources",
     ],
@@ -353,7 +354,6 @@
         "-Wno-unused-parameter",
         "-include netbsd-compat.h",
         "-Wframe-larger-than=66000",
-        "-include private/bsd_sys_param.h",
     ],
 
     local_include_dirs: [
@@ -1490,6 +1490,7 @@
     srcs: [
         "arch-common/bionic/crtbegin_so.c",
         "arch-common/bionic/crtbrand.S",
+        "bionic/android_mallopt.cpp",
         "bionic/gwp_asan_wrappers.cpp",
         "bionic/heap_tagging.cpp",
         "bionic/icu.cpp",
@@ -1508,6 +1509,7 @@
 filegroup {
     name: "libc_sources_static",
     srcs: [
+        "bionic/android_mallopt.cpp",
         "bionic/gwp_asan_wrappers.cpp",
         "bionic/heap_tagging.cpp",
         "bionic/icu_static.cpp",
diff --git a/libc/bionic/android_mallopt.cpp b/libc/bionic/android_mallopt.cpp
new file mode 100644
index 0000000..79e4072
--- /dev/null
+++ b/libc/bionic/android_mallopt.cpp
@@ -0,0 +1,146 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <stdatomic.h>
+
+#include <platform/bionic/malloc.h>
+#include <private/bionic_globals.h>
+
+#include "gwp_asan_wrappers.h"
+#include "malloc_limit.h"
+
+#if !defined(LIBC_STATIC)
+#include <stdio.h>
+
+#include <private/bionic_defs.h>
+
+#include "malloc_heapprofd.h"
+
+extern bool gZygoteChild;
+extern _Atomic bool gZygoteChildProfileable;
+
+bool WriteMallocLeakInfo(FILE* fp);
+bool GetMallocLeakInfo(android_mallopt_leak_info_t* leak_info);
+bool FreeMallocLeakInfo(android_mallopt_leak_info_t* leak_info);
+#endif
+
+// =============================================================================
+// Platform-internal mallopt variant.
+// =============================================================================
+#if !defined(LIBC_STATIC)
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+#endif
+extern "C" bool android_mallopt(int opcode, void* arg, size_t arg_size) {
+  // Functionality available in both static and dynamic libc.
+  if (opcode == M_GET_DECAY_TIME_ENABLED) {
+    if (arg == nullptr || arg_size != sizeof(bool)) {
+      errno = EINVAL;
+      return false;
+    }
+    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_globals->decay_time_enabled);
+    return true;
+  }
+  if (opcode == M_INITIALIZE_GWP_ASAN) {
+    if (arg == nullptr || arg_size != sizeof(android_mallopt_gwp_asan_options_t)) {
+      errno = EINVAL;
+      return false;
+    }
+
+    return EnableGwpAsan(*reinterpret_cast<android_mallopt_gwp_asan_options_t*>(arg));
+  }
+  if (opcode == M_MEMTAG_STACK_IS_ON) {
+    if (arg == nullptr || arg_size != sizeof(bool)) {
+      errno = EINVAL;
+      return false;
+    }
+    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_memtag_stack);
+    return true;
+  }
+  if (opcode == M_SET_ALLOCATION_LIMIT_BYTES) {
+    return LimitEnable(arg, arg_size);
+  }
+
+#if defined(LIBC_STATIC)
+  errno = ENOTSUP;
+  return false;
+#else
+  if (opcode == M_SET_ZYGOTE_CHILD) {
+    if (arg != nullptr || arg_size != 0) {
+      errno = EINVAL;
+      return false;
+    }
+    gZygoteChild = true;
+    return true;
+  }
+  if (opcode == M_INIT_ZYGOTE_CHILD_PROFILING) {
+    if (arg != nullptr || arg_size != 0) {
+      errno = EINVAL;
+      return false;
+    }
+    atomic_store_explicit(&gZygoteChildProfileable, true, memory_order_release);
+    // Also check if heapprofd should start profiling from app startup.
+    HeapprofdInitZygoteChildProfiling();
+    return true;
+  }
+  if (opcode == M_GET_PROCESS_PROFILEABLE) {
+    if (arg == nullptr || arg_size != sizeof(bool)) {
+      errno = EINVAL;
+      return false;
+    }
+    // Native processes are considered profileable. Zygote children are considered
+    // profileable only when appropriately tagged.
+    *reinterpret_cast<bool*>(arg) =
+        !gZygoteChild || atomic_load_explicit(&gZygoteChildProfileable, memory_order_acquire);
+    return true;
+  }
+  if (opcode == M_WRITE_MALLOC_LEAK_INFO_TO_FILE) {
+    if (arg == nullptr || arg_size != sizeof(FILE*)) {
+      errno = EINVAL;
+      return false;
+    }
+    return WriteMallocLeakInfo(reinterpret_cast<FILE*>(arg));
+  }
+  if (opcode == M_GET_MALLOC_LEAK_INFO) {
+    if (arg == nullptr || arg_size != sizeof(android_mallopt_leak_info_t)) {
+      errno = EINVAL;
+      return false;
+    }
+    return GetMallocLeakInfo(reinterpret_cast<android_mallopt_leak_info_t*>(arg));
+  }
+  if (opcode == M_FREE_MALLOC_LEAK_INFO) {
+    if (arg == nullptr || arg_size != sizeof(android_mallopt_leak_info_t)) {
+      errno = EINVAL;
+      return false;
+    }
+    return FreeMallocLeakInfo(reinterpret_cast<android_mallopt_leak_info_t*>(arg));
+  }
+  // Try heapprofd's mallopt, as it handles options not covered here.
+  return HeapprofdMallopt(opcode, arg, arg_size);
+#endif
+}
diff --git a/libc/bionic/fts.c b/libc/bionic/fts.c
index 1287267..c36835e 100644
--- a/libc/bionic/fts.c
+++ b/libc/bionic/fts.c
@@ -29,7 +29,6 @@
  * SUCH DAMAGE.
  */
 
-#include <sys/param.h>	/* ALIGN */
 #include <sys/stat.h>
 
 #include <dirent.h>
@@ -37,6 +36,7 @@
 #include <fcntl.h>
 #include <fts.h>
 #include <limits.h>
+#include <stdalign.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -912,10 +912,14 @@
 	 * be careful that the stat structure is reasonably aligned.  Since the
 	 * fts_name field is declared to be of size 1, the fts_name pointer is
 	 * namelen + 2 before the first possible address of the stat structure.
+	 *
+	 * We can't use the same trick FreeBSD uses here because our fts_name
+	 * is a char[1] rather than a char*. This is also the reason we don't
+	 * need to say `namelen + 1`. We just assume the worst alignment.
 	 */
 	len = sizeof(FTSENT) + namelen;
 	if (!ISSET(FTS_NOSTAT))
-		len += sizeof(struct stat) + ALIGNBYTES;
+		len += alignof(struct stat) + sizeof(struct stat);
 	if ((p = calloc(1, len)) == NULL)
 		return (NULL);
 
@@ -923,7 +927,7 @@
 	p->fts_namelen = namelen;
 	p->fts_instr = FTS_NOINSTR;
 	if (!ISSET(FTS_NOSTAT))
-		p->fts_statp = (struct stat *)ALIGN(p->fts_name + namelen + 2);
+		p->fts_statp = (struct stat *)__builtin_align_up(p->fts_name + namelen + 2, alignof(struct stat));
 	memcpy(p->fts_name, name, namelen);
 
 	return (p);
diff --git a/libc/bionic/libc_init_mte.cpp b/libc/bionic/libc_init_mte.cpp
new file mode 100644
index 0000000..3c8ef7d
--- /dev/null
+++ b/libc/bionic/libc_init_mte.cpp
@@ -0,0 +1,325 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <android/api-level.h>
+#include <elf.h>
+#include <errno.h>
+#include <malloc.h>
+#include <signal.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/auxv.h>
+#include <sys/mman.h>
+
+#include "async_safe/log.h"
+#include "heap_tagging.h"
+#include "libc_init_common.h"
+#include "platform/bionic/macros.h"
+#include "platform/bionic/mte.h"
+#include "platform/bionic/page.h"
+#include "platform/bionic/reserved_signals.h"
+#include "private/KernelArgumentBlock.h"
+#include "private/bionic_asm.h"
+#include "private/bionic_asm_note.h"
+#include "private/bionic_call_ifunc_resolver.h"
+#include "private/bionic_elf_tls.h"
+#include "private/bionic_globals.h"
+#include "private/bionic_tls.h"
+#include "private/elf_note.h"
+#include "pthread_internal.h"
+#include "sys/system_properties.h"
+#include "sysprop_helpers.h"
+
+#ifdef __aarch64__
+extern "C" const char* __gnu_basename(const char* path);
+
+static HeapTaggingLevel __get_memtag_level_from_note(const ElfW(Phdr) * phdr_start, size_t phdr_ct,
+                                                     const ElfW(Addr) load_bias, bool* stack) {
+  const ElfW(Nhdr) * note;
+  const char* desc;
+  if (!__find_elf_note(NT_ANDROID_TYPE_MEMTAG, "Android", phdr_start, phdr_ct, &note, &desc,
+                       load_bias)) {
+    return M_HEAP_TAGGING_LEVEL_TBI;
+  }
+
+  // Previously (in Android 12), if the note was != 4 bytes, we check-failed
+  // here. Let's be more permissive to allow future expansion.
+  if (note->n_descsz < 4) {
+    async_safe_fatal("unrecognized android.memtag note: n_descsz = %d, expected >= 4",
+                     note->n_descsz);
+  }
+
+  // `desc` is always aligned due to ELF requirements, enforced in __find_elf_note().
+  ElfW(Word) note_val = *reinterpret_cast<const ElfW(Word)*>(desc);
+  *stack = (note_val & NT_MEMTAG_STACK) != 0;
+
+  // Warning: In Android 12, any value outside of bits [0..3] resulted in a check-fail.
+  if (!(note_val & (NT_MEMTAG_HEAP | NT_MEMTAG_STACK))) {
+    async_safe_format_log(ANDROID_LOG_INFO, "libc",
+                          "unrecognised memtag note_val did not specificy heap or stack: %u",
+                          note_val);
+    return M_HEAP_TAGGING_LEVEL_TBI;
+  }
+
+  unsigned mode = note_val & NT_MEMTAG_LEVEL_MASK;
+  switch (mode) {
+    case NT_MEMTAG_LEVEL_NONE:
+      // Note, previously (in Android 12), NT_MEMTAG_LEVEL_NONE was
+      // NT_MEMTAG_LEVEL_DEFAULT, which implied SYNC mode. This was never used
+      // by anyone, but we note it (heh) here for posterity, in case the zero
+      // level becomes meaningful, and binaries with this note can be executed
+      // on Android 12 devices.
+      return M_HEAP_TAGGING_LEVEL_TBI;
+    case NT_MEMTAG_LEVEL_ASYNC:
+      return M_HEAP_TAGGING_LEVEL_ASYNC;
+    case NT_MEMTAG_LEVEL_SYNC:
+    default:
+      // We allow future extensions to specify mode 3 (currently unused), with
+      // the idea that it might be used for ASYMM mode or something else. On
+      // this version of Android, it falls back to SYNC mode.
+      return M_HEAP_TAGGING_LEVEL_SYNC;
+  }
+}
+
+// Returns true if there's an environment setting (either sysprop or env var)
+// that should overwrite the ELF note, and places the equivalent heap tagging
+// level into *level.
+static bool get_environment_memtag_setting(HeapTaggingLevel* level) {
+  static const char kMemtagPrognameSyspropPrefix[] = "arm64.memtag.process.";
+  static const char kMemtagGlobalSysprop[] = "persist.arm64.memtag.default";
+  static const char kMemtagOverrideSyspropPrefix[] =
+      "persist.device_config.memory_safety_native.mode_override.process.";
+
+  const char* progname = __libc_shared_globals()->init_progname;
+  if (progname == nullptr) return false;
+
+  const char* basename = __gnu_basename(progname);
+
+  char options_str[PROP_VALUE_MAX];
+  char sysprop_name[512];
+  async_safe_format_buffer(sysprop_name, sizeof(sysprop_name), "%s%s", kMemtagPrognameSyspropPrefix,
+                           basename);
+  char remote_sysprop_name[512];
+  async_safe_format_buffer(remote_sysprop_name, sizeof(remote_sysprop_name), "%s%s",
+                           kMemtagOverrideSyspropPrefix, basename);
+  const char* sys_prop_names[] = {sysprop_name, remote_sysprop_name, kMemtagGlobalSysprop};
+
+  if (!get_config_from_env_or_sysprops("MEMTAG_OPTIONS", sys_prop_names, arraysize(sys_prop_names),
+                                       options_str, sizeof(options_str))) {
+    return false;
+  }
+
+  if (strcmp("sync", options_str) == 0) {
+    *level = M_HEAP_TAGGING_LEVEL_SYNC;
+  } else if (strcmp("async", options_str) == 0) {
+    *level = M_HEAP_TAGGING_LEVEL_ASYNC;
+  } else if (strcmp("off", options_str) == 0) {
+    *level = M_HEAP_TAGGING_LEVEL_TBI;
+  } else {
+    async_safe_format_log(
+        ANDROID_LOG_ERROR, "libc",
+        "unrecognized memtag level: \"%s\" (options are \"sync\", \"async\", or \"off\").",
+        options_str);
+    return false;
+  }
+
+  return true;
+}
+
+// Returns the initial heap tagging level. Note: This function will never return
+// M_HEAP_TAGGING_LEVEL_NONE, if MTE isn't enabled for this process we enable
+// M_HEAP_TAGGING_LEVEL_TBI.
+static HeapTaggingLevel __get_tagging_level(const memtag_dynamic_entries_t* memtag_dynamic_entries,
+                                            const void* phdr_start, size_t phdr_ct,
+                                            uintptr_t load_bias, bool* stack) {
+  HeapTaggingLevel level = M_HEAP_TAGGING_LEVEL_TBI;
+
+  // If the dynamic entries exist, use those. Otherwise, fall back to the old
+  // Android note, which is still used for fully static executables. When
+  // -fsanitize=memtag* is used in newer toolchains, currently both the dynamic
+  // entries and the old note are created, but we'd expect to move to just the
+  // dynamic entries for dynamically linked executables in the future. In
+  // addition, there's still some cleanup of the build system (that uses a
+  // manually-constructed note) needed. For more information about the dynamic
+  // entries, see:
+  // https://github.com/ARM-software/abi-aa/blob/main/memtagabielf64/memtagabielf64.rst#dynamic-section
+  if (memtag_dynamic_entries && memtag_dynamic_entries->has_memtag_mode) {
+    switch (memtag_dynamic_entries->memtag_mode) {
+      case 0:
+        level = M_HEAP_TAGGING_LEVEL_SYNC;
+        break;
+      case 1:
+        level = M_HEAP_TAGGING_LEVEL_ASYNC;
+        break;
+      default:
+        async_safe_format_log(ANDROID_LOG_INFO, "libc",
+                              "unrecognised DT_AARCH64_MEMTAG_MODE value: %u",
+                              memtag_dynamic_entries->memtag_mode);
+    }
+    *stack = memtag_dynamic_entries->memtag_stack;
+  } else {
+    level = __get_memtag_level_from_note(reinterpret_cast<const ElfW(Phdr)*>(phdr_start), phdr_ct,
+                                         load_bias, stack);
+  }
+
+  // We can't short-circuit the environment override, as `stack` is still inherited from the
+  // binary's settings.
+  get_environment_memtag_setting(&level);
+  return level;
+}
+
+static void __enable_mte_signal_handler(int, siginfo_t* info, void*) {
+  if (info->si_code != SI_TIMER) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Got BIONIC_ENABLE_MTE not from SI_TIMER");
+    return;
+  }
+  int tagged_addr_ctrl = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+  if (tagged_addr_ctrl < 0) {
+    async_safe_fatal("failed to PR_GET_TAGGED_ADDR_CTRL: %m");
+  }
+  if ((tagged_addr_ctrl & PR_MTE_TCF_MASK) != PR_MTE_TCF_NONE) {
+    return;
+  }
+  async_safe_format_log(ANDROID_LOG_INFO, "libc",
+                        "Re-enabling MTE, value: %x (tagged_addr_ctrl %lu)",
+                        info->si_value.sival_int, info->si_value.sival_int & PR_MTE_TCF_MASK);
+  tagged_addr_ctrl =
+      (tagged_addr_ctrl & ~PR_MTE_TCF_MASK) | (info->si_value.sival_int & PR_MTE_TCF_MASK);
+  if (prctl(PR_SET_TAGGED_ADDR_CTRL, tagged_addr_ctrl, 0, 0, 0) < 0) {
+    async_safe_fatal("failed to PR_SET_TAGGED_ADDR_CTRL %d: %m", tagged_addr_ctrl);
+  }
+}
+
+static int64_t __get_memtag_upgrade_secs() {
+  char* env = getenv("BIONIC_MEMTAG_UPGRADE_SECS");
+  if (!env) return 0;
+  int64_t timed_upgrade = 0;
+  static const char kAppProcessName[] = "app_process64";
+  const char* progname = __libc_shared_globals()->init_progname;
+  progname = progname ? __gnu_basename(progname) : nullptr;
+  // disable timed upgrade for zygote, as the thread spawned will violate the requirement
+  // that it be single-threaded.
+  if (!progname || strncmp(progname, kAppProcessName, sizeof(kAppProcessName)) != 0) {
+    char* endptr;
+    timed_upgrade = strtoll(env, &endptr, 10);
+    if (*endptr != '\0' || timed_upgrade < 0) {
+      async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                            "Invalid value for BIONIC_MEMTAG_UPGRADE_SECS: %s", env);
+      timed_upgrade = 0;
+    }
+  }
+  // Make sure that this does not get passed to potential processes inheriting
+  // this environment.
+  unsetenv("BIONIC_MEMTAG_UPGRADE_SECS");
+  return timed_upgrade;
+}
+
+// Figure out the desired memory tagging mode (sync/async, heap/globals/stack) for this executable.
+// This function is called from the linker before the main executable is relocated.
+__attribute__((no_sanitize("hwaddress", "memtag"))) void __libc_init_mte(
+    const memtag_dynamic_entries_t* memtag_dynamic_entries, const void* phdr_start, size_t phdr_ct,
+    uintptr_t load_bias) {
+  bool memtag_stack = false;
+  HeapTaggingLevel level =
+      __get_tagging_level(memtag_dynamic_entries, phdr_start, phdr_ct, load_bias, &memtag_stack);
+  if (memtag_stack) __libc_shared_globals()->initial_memtag_stack_abi = true;
+
+  if (int64_t timed_upgrade = __get_memtag_upgrade_secs()) {
+    if (level == M_HEAP_TAGGING_LEVEL_ASYNC) {
+      async_safe_format_log(ANDROID_LOG_INFO, "libc",
+                            "Attempting timed MTE upgrade from async to sync.");
+      __libc_shared_globals()->heap_tagging_upgrade_timer_sec = timed_upgrade;
+      level = M_HEAP_TAGGING_LEVEL_SYNC;
+    } else if (level != M_HEAP_TAGGING_LEVEL_SYNC) {
+      async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                            "Requested timed MTE upgrade from invalid %s to sync. Ignoring.",
+                            DescribeTaggingLevel(level));
+    }
+  }
+  if (level == M_HEAP_TAGGING_LEVEL_SYNC || level == M_HEAP_TAGGING_LEVEL_ASYNC) {
+    unsigned long prctl_arg = PR_TAGGED_ADDR_ENABLE | PR_MTE_TAG_SET_NONZERO;
+    prctl_arg |= (level == M_HEAP_TAGGING_LEVEL_SYNC) ? PR_MTE_TCF_SYNC : PR_MTE_TCF_ASYNC;
+
+    // When entering ASYNC mode, specify that we want to allow upgrading to SYNC by OR'ing in the
+    // SYNC flag. But if the kernel doesn't support specifying multiple TCF modes, fall back to
+    // specifying a single mode.
+    if (prctl(PR_SET_TAGGED_ADDR_CTRL, prctl_arg | PR_MTE_TCF_SYNC, 0, 0, 0) == 0 ||
+        prctl(PR_SET_TAGGED_ADDR_CTRL, prctl_arg, 0, 0, 0) == 0) {
+      __libc_shared_globals()->initial_heap_tagging_level = level;
+
+      struct sigaction action = {};
+      action.sa_flags = SA_SIGINFO | SA_RESTART;
+      action.sa_sigaction = __enable_mte_signal_handler;
+      sigaction(BIONIC_ENABLE_MTE, &action, nullptr);
+      return;
+    }
+  }
+
+  // MTE was either not enabled, or wasn't supported on this device. Try and use
+  // TBI.
+  if (prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE, 0, 0, 0) == 0) {
+    __libc_shared_globals()->initial_heap_tagging_level = M_HEAP_TAGGING_LEVEL_TBI;
+  }
+  // We did not enable MTE, so we do not need to arm the upgrade timer.
+  __libc_shared_globals()->heap_tagging_upgrade_timer_sec = 0;
+}
+
+// Figure out whether we need to map the stack as PROT_MTE.
+// For dynamic executables, this has to be called after loading all
+// DT_NEEDED libraries, in case one of them needs stack MTE.
+__attribute__((no_sanitize("hwaddress", "memtag"))) void __libc_init_mte_stack(void* stack_top) {
+  if (!__libc_shared_globals()->initial_memtag_stack_abi) {
+    return;
+  }
+
+  // Even if the device doesn't support MTE, we have to allocate stack
+  // history buffers for code compiled for stack MTE. That is because the
+  // codegen expects a buffer to be present in TLS_SLOT_STACK_MTE either
+  // way.
+  __get_bionic_tcb()->tls_slot(TLS_SLOT_STACK_MTE) = __allocate_stack_mte_ringbuffer(0, nullptr);
+
+  if (__libc_mte_enabled()) {
+    __libc_shared_globals()->initial_memtag_stack = true;
+    void* pg_start = reinterpret_cast<void*>(page_start(reinterpret_cast<uintptr_t>(stack_top)));
+    if (mprotect(pg_start, page_size(), PROT_READ | PROT_WRITE | PROT_MTE | PROT_GROWSDOWN)) {
+      async_safe_fatal("error: failed to set PROT_MTE on main thread stack: %m");
+    }
+  }
+}
+
+#else   // __aarch64__
+void __libc_init_mte(const memtag_dynamic_entries_t*, const void*, size_t, uintptr_t) {}
+void __libc_init_mte_stack(void*) {}
+#endif  // __aarch64__
+
+bool __libc_mte_enabled() {
+  HeapTaggingLevel lvl = __libc_shared_globals()->initial_heap_tagging_level;
+  return lvl == M_HEAP_TAGGING_LEVEL_SYNC || lvl == M_HEAP_TAGGING_LEVEL_ASYNC;
+}
diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index fac270a..cd96375 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -157,268 +157,6 @@
 
   layout.finish_layout();
 }
-
-#ifdef __aarch64__
-static HeapTaggingLevel __get_memtag_level_from_note(const ElfW(Phdr) * phdr_start, size_t phdr_ct,
-                                                     const ElfW(Addr) load_bias, bool* stack) {
-  const ElfW(Nhdr) * note;
-  const char* desc;
-  if (!__find_elf_note(NT_ANDROID_TYPE_MEMTAG, "Android", phdr_start, phdr_ct, &note, &desc,
-                       load_bias)) {
-    return M_HEAP_TAGGING_LEVEL_TBI;
-  }
-
-  // Previously (in Android 12), if the note was != 4 bytes, we check-failed
-  // here. Let's be more permissive to allow future expansion.
-  if (note->n_descsz < 4) {
-    async_safe_fatal("unrecognized android.memtag note: n_descsz = %d, expected >= 4",
-                     note->n_descsz);
-  }
-
-  // `desc` is always aligned due to ELF requirements, enforced in __find_elf_note().
-  ElfW(Word) note_val = *reinterpret_cast<const ElfW(Word)*>(desc);
-  *stack = (note_val & NT_MEMTAG_STACK) != 0;
-
-  // Warning: In Android 12, any value outside of bits [0..3] resulted in a check-fail.
-  if (!(note_val & (NT_MEMTAG_HEAP | NT_MEMTAG_STACK))) {
-    async_safe_format_log(ANDROID_LOG_INFO, "libc",
-                          "unrecognised memtag note_val did not specificy heap or stack: %u",
-                          note_val);
-    return M_HEAP_TAGGING_LEVEL_TBI;
-  }
-
-  unsigned mode = note_val & NT_MEMTAG_LEVEL_MASK;
-  switch (mode) {
-    case NT_MEMTAG_LEVEL_NONE:
-      // Note, previously (in Android 12), NT_MEMTAG_LEVEL_NONE was
-      // NT_MEMTAG_LEVEL_DEFAULT, which implied SYNC mode. This was never used
-      // by anyone, but we note it (heh) here for posterity, in case the zero
-      // level becomes meaningful, and binaries with this note can be executed
-      // on Android 12 devices.
-      return M_HEAP_TAGGING_LEVEL_TBI;
-    case NT_MEMTAG_LEVEL_ASYNC:
-      return M_HEAP_TAGGING_LEVEL_ASYNC;
-    case NT_MEMTAG_LEVEL_SYNC:
-    default:
-      // We allow future extensions to specify mode 3 (currently unused), with
-      // the idea that it might be used for ASYMM mode or something else. On
-      // this version of Android, it falls back to SYNC mode.
-      return M_HEAP_TAGGING_LEVEL_SYNC;
-  }
-}
-
-// Returns true if there's an environment setting (either sysprop or env var)
-// that should overwrite the ELF note, and places the equivalent heap tagging
-// level into *level.
-static bool get_environment_memtag_setting(HeapTaggingLevel* level) {
-  static const char kMemtagPrognameSyspropPrefix[] = "arm64.memtag.process.";
-  static const char kMemtagGlobalSysprop[] = "persist.arm64.memtag.default";
-  static const char kMemtagOverrideSyspropPrefix[] =
-      "persist.device_config.memory_safety_native.mode_override.process.";
-
-  const char* progname = __libc_shared_globals()->init_progname;
-  if (progname == nullptr) return false;
-
-  const char* basename = __gnu_basename(progname);
-
-  char options_str[PROP_VALUE_MAX];
-  char sysprop_name[512];
-  async_safe_format_buffer(sysprop_name, sizeof(sysprop_name), "%s%s", kMemtagPrognameSyspropPrefix,
-                           basename);
-  char remote_sysprop_name[512];
-  async_safe_format_buffer(remote_sysprop_name, sizeof(remote_sysprop_name), "%s%s",
-                           kMemtagOverrideSyspropPrefix, basename);
-  const char* sys_prop_names[] = {sysprop_name, remote_sysprop_name, kMemtagGlobalSysprop};
-
-  if (!get_config_from_env_or_sysprops("MEMTAG_OPTIONS", sys_prop_names, arraysize(sys_prop_names),
-                                       options_str, sizeof(options_str))) {
-    return false;
-  }
-
-  if (strcmp("sync", options_str) == 0) {
-    *level = M_HEAP_TAGGING_LEVEL_SYNC;
-  } else if (strcmp("async", options_str) == 0) {
-    *level = M_HEAP_TAGGING_LEVEL_ASYNC;
-  } else if (strcmp("off", options_str) == 0) {
-    *level = M_HEAP_TAGGING_LEVEL_TBI;
-  } else {
-    async_safe_format_log(
-        ANDROID_LOG_ERROR, "libc",
-        "unrecognized memtag level: \"%s\" (options are \"sync\", \"async\", or \"off\").",
-        options_str);
-    return false;
-  }
-
-  return true;
-}
-
-// Returns the initial heap tagging level. Note: This function will never return
-// M_HEAP_TAGGING_LEVEL_NONE, if MTE isn't enabled for this process we enable
-// M_HEAP_TAGGING_LEVEL_TBI.
-static HeapTaggingLevel __get_tagging_level(const memtag_dynamic_entries_t* memtag_dynamic_entries,
-                                            const void* phdr_start, size_t phdr_ct,
-                                            uintptr_t load_bias, bool* stack) {
-  HeapTaggingLevel level = M_HEAP_TAGGING_LEVEL_TBI;
-
-  // If the dynamic entries exist, use those. Otherwise, fall back to the old
-  // Android note, which is still used for fully static executables. When
-  // -fsanitize=memtag* is used in newer toolchains, currently both the dynamic
-  // entries and the old note are created, but we'd expect to move to just the
-  // dynamic entries for dynamically linked executables in the future. In
-  // addition, there's still some cleanup of the build system (that uses a
-  // manually-constructed note) needed. For more information about the dynamic
-  // entries, see:
-  // https://github.com/ARM-software/abi-aa/blob/main/memtagabielf64/memtagabielf64.rst#dynamic-section
-  if (memtag_dynamic_entries && memtag_dynamic_entries->has_memtag_mode) {
-    switch (memtag_dynamic_entries->memtag_mode) {
-      case 0:
-        level = M_HEAP_TAGGING_LEVEL_SYNC;
-        break;
-      case 1:
-        level = M_HEAP_TAGGING_LEVEL_ASYNC;
-        break;
-      default:
-        async_safe_format_log(ANDROID_LOG_INFO, "libc",
-                              "unrecognised DT_AARCH64_MEMTAG_MODE value: %u",
-                              memtag_dynamic_entries->memtag_mode);
-    }
-    *stack = memtag_dynamic_entries->memtag_stack;
-  } else {
-    level = __get_memtag_level_from_note(reinterpret_cast<const ElfW(Phdr)*>(phdr_start), phdr_ct,
-                                         load_bias, stack);
-  }
-
-  // We can't short-circuit the environment override, as `stack` is still inherited from the
-  // binary's settings.
-  get_environment_memtag_setting(&level);
-  return level;
-}
-
-static void __enable_mte_signal_handler(int, siginfo_t* info, void*) {
-  if (info->si_code != SI_TIMER) {
-    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Got BIONIC_ENABLE_MTE not from SI_TIMER");
-    return;
-  }
-  int tagged_addr_ctrl = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
-  if (tagged_addr_ctrl < 0) {
-    async_safe_fatal("failed to PR_GET_TAGGED_ADDR_CTRL: %m");
-  }
-  if ((tagged_addr_ctrl & PR_MTE_TCF_MASK) != PR_MTE_TCF_NONE) {
-    return;
-  }
-  async_safe_format_log(ANDROID_LOG_INFO, "libc",
-                        "Re-enabling MTE, value: %x (tagged_addr_ctrl %lu)",
-                        info->si_value.sival_int, info->si_value.sival_int & PR_MTE_TCF_MASK);
-  tagged_addr_ctrl =
-      (tagged_addr_ctrl & ~PR_MTE_TCF_MASK) | (info->si_value.sival_int & PR_MTE_TCF_MASK);
-  if (prctl(PR_SET_TAGGED_ADDR_CTRL, tagged_addr_ctrl, 0, 0, 0) < 0) {
-    async_safe_fatal("failed to PR_SET_TAGGED_ADDR_CTRL %d: %m", tagged_addr_ctrl);
-  }
-}
-
-static int64_t __get_memtag_upgrade_secs() {
-  char* env = getenv("BIONIC_MEMTAG_UPGRADE_SECS");
-  if (!env) return 0;
-  int64_t timed_upgrade = 0;
-  static const char kAppProcessName[] = "app_process64";
-  const char* progname = __libc_shared_globals()->init_progname;
-  progname = progname ? __gnu_basename(progname) : nullptr;
-  // disable timed upgrade for zygote, as the thread spawned will violate the requirement
-  // that it be single-threaded.
-  if (!progname || strncmp(progname, kAppProcessName, sizeof(kAppProcessName)) != 0) {
-    char* endptr;
-    timed_upgrade = strtoll(env, &endptr, 10);
-    if (*endptr != '\0' || timed_upgrade < 0) {
-      async_safe_format_log(ANDROID_LOG_ERROR, "libc",
-                            "Invalid value for BIONIC_MEMTAG_UPGRADE_SECS: %s", env);
-      timed_upgrade = 0;
-    }
-  }
-  // Make sure that this does not get passed to potential processes inheriting
-  // this environment.
-  unsetenv("BIONIC_MEMTAG_UPGRADE_SECS");
-  return timed_upgrade;
-}
-
-// Figure out the desired memory tagging mode (sync/async, heap/globals/stack) for this executable.
-// This function is called from the linker before the main executable is relocated.
-__attribute__((no_sanitize("hwaddress", "memtag"))) void __libc_init_mte(
-    const memtag_dynamic_entries_t* memtag_dynamic_entries, const void* phdr_start, size_t phdr_ct,
-    uintptr_t load_bias) {
-  bool memtag_stack = false;
-  HeapTaggingLevel level =
-      __get_tagging_level(memtag_dynamic_entries, phdr_start, phdr_ct, load_bias, &memtag_stack);
-  if (memtag_stack) __libc_shared_globals()->initial_memtag_stack_abi = true;
-
-  if (int64_t timed_upgrade = __get_memtag_upgrade_secs()) {
-    if (level == M_HEAP_TAGGING_LEVEL_ASYNC) {
-      async_safe_format_log(ANDROID_LOG_INFO, "libc",
-                            "Attempting timed MTE upgrade from async to sync.");
-      __libc_shared_globals()->heap_tagging_upgrade_timer_sec = timed_upgrade;
-      level = M_HEAP_TAGGING_LEVEL_SYNC;
-    } else if (level != M_HEAP_TAGGING_LEVEL_SYNC) {
-      async_safe_format_log(
-          ANDROID_LOG_ERROR, "libc",
-          "Requested timed MTE upgrade from invalid %s to sync. Ignoring.",
-          DescribeTaggingLevel(level));
-    }
-  }
-  if (level == M_HEAP_TAGGING_LEVEL_SYNC || level == M_HEAP_TAGGING_LEVEL_ASYNC) {
-    unsigned long prctl_arg = PR_TAGGED_ADDR_ENABLE | PR_MTE_TAG_SET_NONZERO;
-    prctl_arg |= (level == M_HEAP_TAGGING_LEVEL_SYNC) ? PR_MTE_TCF_SYNC : PR_MTE_TCF_ASYNC;
-
-    // When entering ASYNC mode, specify that we want to allow upgrading to SYNC by OR'ing in the
-    // SYNC flag. But if the kernel doesn't support specifying multiple TCF modes, fall back to
-    // specifying a single mode.
-    if (prctl(PR_SET_TAGGED_ADDR_CTRL, prctl_arg | PR_MTE_TCF_SYNC, 0, 0, 0) == 0 ||
-        prctl(PR_SET_TAGGED_ADDR_CTRL, prctl_arg, 0, 0, 0) == 0) {
-      __libc_shared_globals()->initial_heap_tagging_level = level;
-
-      struct sigaction action = {};
-      action.sa_flags = SA_SIGINFO | SA_RESTART;
-      action.sa_sigaction = __enable_mte_signal_handler;
-      sigaction(BIONIC_ENABLE_MTE, &action, nullptr);
-      return;
-    }
-  }
-
-  // MTE was either not enabled, or wasn't supported on this device. Try and use
-  // TBI.
-  if (prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE, 0, 0, 0) == 0) {
-    __libc_shared_globals()->initial_heap_tagging_level = M_HEAP_TAGGING_LEVEL_TBI;
-  }
-  // We did not enable MTE, so we do not need to arm the upgrade timer.
-  __libc_shared_globals()->heap_tagging_upgrade_timer_sec = 0;
-}
-
-// Figure out whether we need to map the stack as PROT_MTE.
-// For dynamic executables, this has to be called after loading all
-// DT_NEEDED libraries, in case one of them needs stack MTE.
-__attribute__((no_sanitize("hwaddress", "memtag"))) void __libc_init_mte_stack(void* stack_top) {
-  if (!__libc_shared_globals()->initial_memtag_stack_abi) {
-    return;
-  }
-
-  // Even if the device doesn't support MTE, we have to allocate stack
-  // history buffers for code compiled for stack MTE. That is because the
-  // codegen expects a buffer to be present in TLS_SLOT_STACK_MTE either
-  // way.
-  __get_bionic_tcb()->tls_slot(TLS_SLOT_STACK_MTE) = __allocate_stack_mte_ringbuffer(0, nullptr);
-
-  if (__libc_mte_enabled()) {
-    __libc_shared_globals()->initial_memtag_stack = true;
-    void* pg_start = reinterpret_cast<void*>(page_start(reinterpret_cast<uintptr_t>(stack_top)));
-    if (mprotect(pg_start, page_size(), PROT_READ | PROT_WRITE | PROT_MTE | PROT_GROWSDOWN)) {
-      async_safe_fatal("error: failed to set PROT_MTE on main thread stack: %m");
-    }
-  }
-}
-
-#else   // __aarch64__
-void __libc_init_mte(const memtag_dynamic_entries_t*, const void*, size_t, uintptr_t) {}
-void __libc_init_mte_stack(void*) {}
-#endif  // __aarch64__
-
 void __libc_init_profiling_handlers() {
   // The dynamic variant of this function is more interesting, but this
   // at least ensures that static binaries aren't killed by the kernel's
@@ -520,8 +258,3 @@
   BIONIC_USED_BEFORE_LINKER_RELOCATES static libc_shared_globals globals;
   return &globals;
 }
-
-__LIBC_HIDDEN__ bool __libc_mte_enabled() {
-  HeapTaggingLevel lvl = __libc_shared_globals()->initial_heap_tagging_level;
-  return lvl == M_HEAP_TAGGING_LEVEL_SYNC || lvl == M_HEAP_TAGGING_LEVEL_ASYNC;
-}
diff --git a/libc/bionic/malloc_common.cpp b/libc/bionic/malloc_common.cpp
index 596a1fc..441d884 100644
--- a/libc/bionic/malloc_common.cpp
+++ b/libc/bionic/malloc_common.cpp
@@ -332,44 +332,6 @@
 #endif
 // =============================================================================
 
-// =============================================================================
-// Platform-internal mallopt variant.
-// =============================================================================
-#if defined(LIBC_STATIC)
-extern "C" bool android_mallopt(int opcode, void* arg, size_t arg_size) {
-  if (opcode == M_SET_ALLOCATION_LIMIT_BYTES) {
-    return LimitEnable(arg, arg_size);
-  }
-  if (opcode == M_INITIALIZE_GWP_ASAN) {
-    if (arg == nullptr || arg_size != sizeof(android_mallopt_gwp_asan_options_t)) {
-      errno = EINVAL;
-      return false;
-    }
-
-    return EnableGwpAsan(*reinterpret_cast<android_mallopt_gwp_asan_options_t*>(arg));
-  }
-  if (opcode == M_MEMTAG_STACK_IS_ON) {
-    if (arg == nullptr || arg_size != sizeof(bool)) {
-      errno = EINVAL;
-      return false;
-    }
-    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_memtag_stack);
-    return true;
-  }
-  if (opcode == M_GET_DECAY_TIME_ENABLED) {
-    if (arg == nullptr || arg_size != sizeof(bool)) {
-      errno = EINVAL;
-      return false;
-    }
-    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_globals->decay_time_enabled);
-    return true;
-  }
-  errno = ENOTSUP;
-  return false;
-}
-#endif
-// =============================================================================
-
 static constexpr MallocDispatch __libc_malloc_default_dispatch __attribute__((unused)) = {
   Malloc(calloc),
   Malloc(free),
diff --git a/libc/bionic/malloc_common_dynamic.cpp b/libc/bionic/malloc_common_dynamic.cpp
index 6db6251..7b6d7d4 100644
--- a/libc/bionic/malloc_common_dynamic.cpp
+++ b/libc/bionic/malloc_common_dynamic.cpp
@@ -80,7 +80,7 @@
 
 _Atomic bool gGlobalsMutating = false;
 
-static bool gZygoteChild = false;
+bool gZygoteChild = false;
 
 // In a Zygote child process, this is set to true if profiling of this process
 // is allowed. Note that this is set at a later time than gZygoteChild. The
@@ -89,7 +89,7 @@
 // domains if applicable). These two flags are read by the
 // BIONIC_SIGNAL_PROFILER handler, which does nothing if the process is not
 // profileable.
-static _Atomic bool gZygoteChildProfileable = false;
+_Atomic bool gZygoteChildProfileable = false;
 
 // =============================================================================
 
@@ -471,93 +471,6 @@
 }
 // =============================================================================
 
-// =============================================================================
-// Platform-internal mallopt variant.
-// =============================================================================
-__BIONIC_WEAK_FOR_NATIVE_BRIDGE
-extern "C" bool android_mallopt(int opcode, void* arg, size_t arg_size) {
-  if (opcode == M_SET_ZYGOTE_CHILD) {
-    if (arg != nullptr || arg_size != 0) {
-      errno = EINVAL;
-      return false;
-    }
-    gZygoteChild = true;
-    return true;
-  }
-  if (opcode == M_INIT_ZYGOTE_CHILD_PROFILING) {
-    if (arg != nullptr || arg_size != 0) {
-      errno = EINVAL;
-      return false;
-    }
-    atomic_store_explicit(&gZygoteChildProfileable, true, memory_order_release);
-    // Also check if heapprofd should start profiling from app startup.
-    HeapprofdInitZygoteChildProfiling();
-    return true;
-  }
-  if (opcode == M_GET_PROCESS_PROFILEABLE) {
-    if (arg == nullptr || arg_size != sizeof(bool)) {
-      errno = EINVAL;
-      return false;
-    }
-    // Native processes are considered profileable. Zygote children are considered
-    // profileable only when appropriately tagged.
-    *reinterpret_cast<bool*>(arg) =
-        !gZygoteChild || atomic_load_explicit(&gZygoteChildProfileable, memory_order_acquire);
-    return true;
-  }
-  if (opcode == M_SET_ALLOCATION_LIMIT_BYTES) {
-    return LimitEnable(arg, arg_size);
-  }
-  if (opcode == M_WRITE_MALLOC_LEAK_INFO_TO_FILE) {
-    if (arg == nullptr || arg_size != sizeof(FILE*)) {
-      errno = EINVAL;
-      return false;
-    }
-    return WriteMallocLeakInfo(reinterpret_cast<FILE*>(arg));
-  }
-  if (opcode == M_GET_MALLOC_LEAK_INFO) {
-    if (arg == nullptr || arg_size != sizeof(android_mallopt_leak_info_t)) {
-      errno = EINVAL;
-      return false;
-    }
-    return GetMallocLeakInfo(reinterpret_cast<android_mallopt_leak_info_t*>(arg));
-  }
-  if (opcode == M_FREE_MALLOC_LEAK_INFO) {
-    if (arg == nullptr || arg_size != sizeof(android_mallopt_leak_info_t)) {
-      errno = EINVAL;
-      return false;
-    }
-    return FreeMallocLeakInfo(reinterpret_cast<android_mallopt_leak_info_t*>(arg));
-  }
-  if (opcode == M_INITIALIZE_GWP_ASAN) {
-    if (arg == nullptr || arg_size != sizeof(android_mallopt_gwp_asan_options_t)) {
-      errno = EINVAL;
-      return false;
-    }
-
-    return EnableGwpAsan(*reinterpret_cast<android_mallopt_gwp_asan_options_t*>(arg));
-  }
-  if (opcode == M_MEMTAG_STACK_IS_ON) {
-    if (arg == nullptr || arg_size != sizeof(bool)) {
-      errno = EINVAL;
-      return false;
-    }
-    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_memtag_stack);
-    return true;
-  }
-  if (opcode == M_GET_DECAY_TIME_ENABLED) {
-    if (arg == nullptr || arg_size != sizeof(bool)) {
-      errno = EINVAL;
-      return false;
-    }
-    *reinterpret_cast<bool*>(arg) = atomic_load(&__libc_globals->decay_time_enabled);
-    return true;
-  }
-  // Try heapprofd's mallopt, as it handles options not covered here.
-  return HeapprofdMallopt(opcode, arg, arg_size);
-}
-// =============================================================================
-
 #if !defined(__LP64__) && defined(__arm__)
 // =============================================================================
 // Old platform only functions that some old 32 bit apps are still using.
diff --git a/libc/bionic/stdlib_l.cpp b/libc/bionic/stdlib_l.cpp
index a636d08..58a9079 100644
--- a/libc/bionic/stdlib_l.cpp
+++ b/libc/bionic/stdlib_l.cpp
@@ -26,17 +26,11 @@
  * SUCH DAMAGE.
  */
 
+#define __BIONIC_STDLIB_INLINE /* Out of line. */
 #include <stdlib.h>
-#include <xlocale.h>
+#include <bits/stdlib_inlines.h>
 
-double strtod_l(const char* s, char** end_ptr, locale_t) {
-  return strtod(s, end_ptr);
-}
-
-float strtof_l(const char* s, char** end_ptr, locale_t) {
-  return strtof(s, end_ptr);
-}
-
+// strtold_l was introduced in API level 21, so it isn't polyfilled any more.
 long double strtold_l(const char* s, char** end_ptr, locale_t) {
   return strtold(s, end_ptr);
 }
diff --git a/libc/dns/net/gethnamaddr.c b/libc/dns/net/gethnamaddr.c
index add124f..1ffabfa 100644
--- a/libc/dns/net/gethnamaddr.c
+++ b/libc/dns/net/gethnamaddr.c
@@ -495,7 +495,7 @@
 	*he = NO_RECOVERY;
 	return NULL;
 success:
-	bp = (char *)ALIGN(bp);
+	bp = __builtin_align_up(bp, sizeof(uintptr_t));
 	n = (int)(ap - aliases);
 	qlen = (n + 1) * sizeof(*hent->h_aliases);
 	if ((size_t)(ep - bp) < qlen)
@@ -616,7 +616,7 @@
 	}
 
 	// Fix alignment after variable-length data.
-	ptr = (char*)ALIGN(ptr);
+	ptr = __builtin_align_up(ptr, sizeof(uintptr_t));
 
 	int aliases_len = ((int)(aliases - aliases_ptrs) + 1) * sizeof(*hp->h_aliases);
 	if (ptr + aliases_len > hbuf_end) {
@@ -653,7 +653,7 @@
 	}
 
 	// Fix alignment after variable-length data.
-	ptr = (char*)ALIGN(ptr);
+	ptr = __builtin_align_up(ptr, sizeof(uintptr_t));
 
 	int addrs_len = ((int)(addr_p - addr_ptrs) + 1) * sizeof(*hp->h_addr_list);
 	if (ptr + addrs_len > hbuf_end) {
diff --git a/libc/dns/net/sethostent.c b/libc/dns/net/sethostent.c
index 5c4bdb5..8ea4315 100644
--- a/libc/dns/net/sethostent.c
+++ b/libc/dns/net/sethostent.c
@@ -198,7 +198,7 @@
 				HENT_SCOPY(aliases[anum], hp->h_aliases[anum],
 				    ptr, len);
 			}
-			ptr = (void *)ALIGN(ptr);
+			ptr = __builtin_align_up(ptr, sizeof(uintptr_t));
 			if ((size_t)(ptr - buf) >= info->buflen)
 				goto nospc;
 		}
diff --git a/libc/execinfo/include/execinfo.h b/libc/execinfo/include/execinfo.h
index e092c00..c8f9e21 100644
--- a/libc/execinfo/include/execinfo.h
+++ b/libc/execinfo/include/execinfo.h
@@ -30,8 +30,10 @@
 
 /*
  * This file is exported as part of libexecinfo for use with musl, which doesn't
- * define __INTRODUCED_IN.  Stub it out.
+ * define __INTRODUCED_IN or __BIONIC_AVAILABILITY_GUARD.  Stub them out.
  */
 #define __INTRODUCED_IN(x)
+#define __BIONIC_AVAILABILITY_GUARD(x) 1
 #include <bionic/execinfo.h>
+#undef __BIONIC_AVAILABILITY_GUARD
 #undef __INTRODUCED_IN
diff --git a/libc/include/android/api-level.h b/libc/include/android/api-level.h
index 1bde3a5..c9536c1 100644
--- a/libc/include/android/api-level.h
+++ b/libc/include/android/api-level.h
@@ -189,7 +189,11 @@
  *
  * Available since API level 24.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int android_get_application_target_sdk_version() __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 #if __ANDROID_API__ < 29
 
diff --git a/libc/include/android/crash_detail.h b/libc/include/android/crash_detail.h
index 946a3ab..fd1312a 100644
--- a/libc/include/android/crash_detail.h
+++ b/libc/include/android/crash_detail.h
@@ -33,9 +33,10 @@
  * @brief Attach extra information to android crashes.
  */
 
-#include <stddef.h>
 #include <sys/cdefs.h>
 
+#include <stddef.h>
+
 __BEGIN_DECLS
 
 typedef struct crash_detail_t crash_detail_t;
@@ -79,6 +80,8 @@
  *
  * \return a handle to the extra crash detail.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 crash_detail_t* _Nullable android_crash_detail_register(
     const void* _Nonnull name, size_t name_size, const void* _Nullable data, size_t data_size) __INTRODUCED_IN(35);
 
@@ -122,5 +125,7 @@
  * \param name_size number of bytes of the buffer pointed to by name
  */
 void android_crash_detail_replace_name(crash_detail_t* _Nonnull crash_detail, const void* _Nonnull name, size_t name_size) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 __END_DECLS
diff --git a/libc/include/android/dlext.h b/libc/include/android/dlext.h
index 842ceea..d8d2752 100644
--- a/libc/include/android/dlext.h
+++ b/libc/include/android/dlext.h
@@ -16,10 +16,11 @@
 
 #pragma once
 
+#include <sys/cdefs.h>
+
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
-#include <sys/cdefs.h>
 #include <sys/types.h>  /* for off64_t */
 
 /**
diff --git a/libc/include/android/fdsan.h b/libc/include/android/fdsan.h
index 4540498..a04fc7e 100644
--- a/libc/include/android/fdsan.h
+++ b/libc/include/android/fdsan.h
@@ -28,9 +28,10 @@
 
 #pragma once
 
+#include <sys/cdefs.h>
+
 #include <stdbool.h>
 #include <stdint.h>
-#include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
@@ -134,6 +135,8 @@
 /*
  * Create an owner tag with the specified type and least significant 56 bits of tag.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 uint64_t android_fdsan_create_owner_tag(enum android_fdsan_owner_type type, uint64_t tag) __INTRODUCED_IN(29) __attribute__((__weak__));
 
 /*
@@ -168,6 +171,8 @@
  * Get an owner tag's value, with the type masked off.
  */
 uint64_t android_fdsan_get_tag_value(uint64_t tag) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 
 enum android_fdsan_error_level {
   // No errors.
@@ -186,6 +191,8 @@
 /*
  * Get the error level.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 enum android_fdsan_error_level android_fdsan_get_error_level() __INTRODUCED_IN(29) __attribute__((__weak__));
 
 /*
@@ -203,9 +210,15 @@
  * (e.g. postfork).
  */
 enum android_fdsan_error_level android_fdsan_set_error_level(enum android_fdsan_error_level new_level) __INTRODUCED_IN(29) __attribute__((__weak__));
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 
 /*
  * Set the error level to the global setting if available, or a default value.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 enum android_fdsan_error_level android_fdsan_set_error_level_from_property(enum android_fdsan_error_level default_level) __INTRODUCED_IN(30) __attribute__((__weak__));
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 __END_DECLS
diff --git a/libc/include/android/legacy_stdlib_inlines.h b/libc/include/android/legacy_stdlib_inlines.h
index a5a07ef..d228e67 100644
--- a/libc/include/android/legacy_stdlib_inlines.h
+++ b/libc/include/android/legacy_stdlib_inlines.h
@@ -30,22 +30,9 @@
 
 #include <sys/cdefs.h>
 
-
 #if __ANDROID_API__ < 26
 
-#include <stdlib.h>
-#include <xlocale.h>
-
-__BEGIN_DECLS
-
-static __inline double strtod_l(const char* _Nonnull __s, char* _Nullable * _Nullable __end_ptr, locale_t _Nonnull __l) {
-  return strtod(__s, __end_ptr);
-}
-
-static __inline float strtof_l(const char* _Nonnull __s, char* _Nullable * _Nullable __end_ptr, locale_t _Nonnull __l) {
-  return strtof(__s, __end_ptr);
-}
-
-__END_DECLS
+#define __BIONIC_THREADS_INLINE static __inline
+#include <bits/stdlib_inlines.h>
 
 #endif
diff --git a/libc/include/android/set_abort_message.h b/libc/include/android/set_abort_message.h
index a778057..6ad5678 100644
--- a/libc/include/android/set_abort_message.h
+++ b/libc/include/android/set_abort_message.h
@@ -33,10 +33,11 @@
  * @brief The android_set_abort_message() function.
  */
 
+#include <sys/cdefs.h>
+
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
-#include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
diff --git a/libc/include/android/versioning.h b/libc/include/android/versioning.h
index b09cf14..1676a72 100644
--- a/libc/include/android/versioning.h
+++ b/libc/include/android/versioning.h
@@ -32,6 +32,11 @@
 // load even on systems too old to contain the API, but calls must be guarded
 // with `__builtin_available(android api_level, *)` to avoid segfaults.
 #define __BIONIC_AVAILABILITY(__what, ...) __attribute__((__availability__(android,__what __VA_OPT__(,) __VA_ARGS__)))
+
+// When the caller is using weak API references, we should expose the decls for
+// APIs which are not available in the caller's minSdkVersion, otherwise there's
+// no way to take advantage of the weak references.
+#define __BIONIC_AVAILABILITY_GUARD(api_level) 1
 #else
 // The 'strict' flag is required for NDK clients where the code was not written
 // to handle the case where the API was available at build-time but not at
@@ -40,6 +45,17 @@
 // compile in this mode (or worse, if the build doesn't use
 // -Werror=unguarded-availability, it would build but crash at runtime).
 #define __BIONIC_AVAILABILITY(__what, ...) __attribute__((__availability__(android,strict,__what __VA_OPT__(,) __VA_ARGS__)))
+
+// When the caller is using strict API references, we hide APIs which are not
+// available in the caller's minSdkVersion. This is a bionic-only deviation in
+// behavior from the rest of the NDK headers, but it's necessary to maintain
+// source compatibility with 3p libraries that either can't correctly detect API
+// availability (either incorrectly detecting as always-available or as
+// never-available, but neither is true), or define their own polyfills which
+// conflict with our declarations.
+//
+// https://github.com/android/ndk/issues/2081
+#define __BIONIC_AVAILABILITY_GUARD(api_level) (__ANDROID_MIN_SDK_VERSION__ >= (api_level))
 #endif
 
 #pragma clang diagnostic push
@@ -69,4 +85,5 @@
 #if defined(__ANDROID_VNDK__)
 #undef __BIONIC_AVAILABILITY
 #define __BIONIC_AVAILABILITY(api_level, ...)
+#define __BIONIC_AVAILABILITY_GUARD(api_level) 1
 #endif // defined(__ANDROID_VNDK__)
diff --git a/libc/include/arpa/ftp.h b/libc/include/arpa/ftp.h
index 081c037..fecbf7f 100644
--- a/libc/include/arpa/ftp.h
+++ b/libc/include/arpa/ftp.h
@@ -34,6 +34,8 @@
 #ifndef _ARPA_FTP_H_
 #define	_ARPA_FTP_H_
 
+#include <sys/cdefs.h>
+
 /* Definitions for FTP; see RFC-765. */
 
 /*
diff --git a/libc/include/arpa/inet.h b/libc/include/arpa/inet.h
index f00f2c1..ce9dd93 100644
--- a/libc/include/arpa/inet.h
+++ b/libc/include/arpa/inet.h
@@ -29,9 +29,10 @@
 #ifndef _ARPA_INET_H_
 #define _ARPA_INET_H_
 
+#include <sys/cdefs.h>
+
 #include <netinet/in.h>
 #include <stdint.h>
-#include <sys/cdefs.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/arpa/nameser.h b/libc/include/arpa/nameser.h
index 97109ee..3e0025e 100644
--- a/libc/include/arpa/nameser.h
+++ b/libc/include/arpa/nameser.h
@@ -55,9 +55,10 @@
 
 #define BIND_4_COMPAT
 
-#include <sys/types.h>
 #include <sys/cdefs.h>
 
+#include <sys/types.h>
+
 /*
  * Revision information.  This is the release date in YYYYMMDD format.
  * It can change every day so the right thing to do with it is use it
@@ -547,6 +548,8 @@
 #define ns_sprintrrf __ns_sprintrrf
 #endif
 
+
+#if __BIONIC_AVAILABILITY_GUARD(22)
 int ns_msg_getflag(ns_msg __handle, int __flag) __INTRODUCED_IN(22);
 uint16_t ns_get16(const u_char* _Nonnull __src) __INTRODUCED_IN(22);
 uint32_t ns_get32(const u_char* _Nonnull __src) __INTRODUCED_IN(22);
@@ -570,6 +573,8 @@
 
 int ns_makecanon(const char* _Nonnull __src, char* _Nonnull __dst, size_t __dst_size) __INTRODUCED_IN(22);
 int ns_samename(const char* _Nonnull __lhs, const char* _Nonnull __rhs) __INTRODUCED_IN(22);
+#endif /* __BIONIC_AVAILABILITY_GUARD(22) */
+
 
 __END_DECLS
 
diff --git a/libc/include/arpa/nameser_compat.h b/libc/include/arpa/nameser_compat.h
index e4e9335..027e5ca 100644
--- a/libc/include/arpa/nameser_compat.h
+++ b/libc/include/arpa/nameser_compat.h
@@ -40,9 +40,10 @@
 #ifndef _ARPA_NAMESER_COMPAT_
 #define	_ARPA_NAMESER_COMPAT_
 
-#include <endian.h>
 #include <sys/cdefs.h>
 
+#include <endian.h>
+
 #define	__BIND		19950621	/* (DEAD) interface version stamp. */
 
 /*
diff --git a/libc/include/arpa/telnet.h b/libc/include/arpa/telnet.h
index 758e9b8..30d8f21 100644
--- a/libc/include/arpa/telnet.h
+++ b/libc/include/arpa/telnet.h
@@ -33,6 +33,8 @@
 #ifndef _ARPA_TELNET_H_
 #define	_ARPA_TELNET_H_
 
+#include <sys/cdefs.h>
+
 /*
  * Definitions for the TELNET protocol.
  */
diff --git a/libc/include/bits/bionic_multibyte_result.h b/libc/include/bits/bionic_multibyte_result.h
index 0d5cf21..930e67c 100644
--- a/libc/include/bits/bionic_multibyte_result.h
+++ b/libc/include/bits/bionic_multibyte_result.h
@@ -34,9 +34,10 @@
  * conversion APIs defined by C.
  */
 
-#include <stddef.h>
 #include <sys/cdefs.h>
 
+#include <stddef.h>
+
 __BEGIN_DECLS
 
 /**
diff --git a/libc/include/bits/fortify/poll.h b/libc/include/bits/fortify/poll.h
index f2e27d7..1b4a5bf 100644
--- a/libc/include/bits/fortify/poll.h
+++ b/libc/include/bits/fortify/poll.h
@@ -30,9 +30,17 @@
 #error "Never include this file directly; instead, include <poll.h>"
 #endif
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int __poll_chk(struct pollfd* _Nullable, nfds_t, int, size_t) __INTRODUCED_IN(23);
 int __ppoll_chk(struct pollfd* _Nullable, nfds_t, const struct timespec* _Nullable, const sigset_t* _Nullable, size_t) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int __ppoll64_chk(struct pollfd* _Nullable, nfds_t, const struct timespec* _Nullable, const sigset64_t* _Nullable, size_t) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 #if defined(__BIONIC_FORTIFY)
 #define __bos_fd_count_trivially_safe(bos_val, fds, fd_count)              \
diff --git a/libc/include/bits/fortify/socket.h b/libc/include/bits/fortify/socket.h
index 1c3605b..bd626f9 100644
--- a/libc/include/bits/fortify/socket.h
+++ b/libc/include/bits/fortify/socket.h
@@ -30,7 +30,11 @@
 #error "Never include this file directly; instead, include <sys/socket.h>"
 #endif
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 ssize_t __sendto_chk(int, const void* _Nonnull, size_t, size_t, int, const struct sockaddr* _Nullable, socklen_t) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 ssize_t __recvfrom_chk(int, void* _Nullable, size_t, size_t, int, struct sockaddr* _Nullable, socklen_t* _Nullable);
 
 #if defined(__BIONIC_FORTIFY)
diff --git a/libc/include/bits/fortify/stdio.h b/libc/include/bits/fortify/stdio.h
index e4607e0..f9faeba 100644
--- a/libc/include/bits/fortify/stdio.h
+++ b/libc/include/bits/fortify/stdio.h
@@ -31,8 +31,12 @@
 #endif
 
 char* _Nullable __fgets_chk(char* _Nonnull, int, FILE* _Nonnull, size_t);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 size_t __fread_chk(void* _Nonnull, size_t, size_t, FILE* _Nonnull, size_t) __INTRODUCED_IN(24);
 size_t __fwrite_chk(const void* _Nonnull, size_t, size_t, FILE* _Nonnull, size_t) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 #if defined(__BIONIC_FORTIFY) && !defined(__BIONIC_NO_STDIO_FORTIFY)
 
diff --git a/libc/include/bits/fortify/string.h b/libc/include/bits/fortify/string.h
index 041967b..6f0ee4a 100644
--- a/libc/include/bits/fortify/string.h
+++ b/libc/include/bits/fortify/string.h
@@ -30,8 +30,12 @@
 #error "Never include this file directly; instead, include <string.h>"
 #endif
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void* _Nullable __memchr_chk(const void* _Nonnull, int, size_t, size_t) __INTRODUCED_IN(23);
 void* _Nullable __memrchr_chk(const void* _Nonnull, int, size_t, size_t) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 char* _Nonnull __stpncpy_chk2(char* _Nonnull, const char* _Nonnull, size_t, size_t, size_t);
 char* _Nonnull __strncpy_chk2(char* _Nonnull, const char* _Nonnull, size_t, size_t, size_t);
 size_t __strlcpy_chk(char* _Nonnull, const char* _Nonnull, size_t, size_t);
diff --git a/libc/include/bits/fortify/unistd.h b/libc/include/bits/fortify/unistd.h
index 7eda1a6..9acb942 100644
--- a/libc/include/bits/fortify/unistd.h
+++ b/libc/include/bits/fortify/unistd.h
@@ -29,24 +29,52 @@
 #error "Never include this file directly; instead, include <unistd.h>"
 #endif
 
-char* _Nullable __getcwd_chk(char* _Nullable, size_t, size_t) __INTRODUCED_IN(24);
 
+#if __BIONIC_AVAILABILITY_GUARD(24)
+char* _Nullable __getcwd_chk(char* _Nullable, size_t, size_t) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 ssize_t __pread_chk(int, void* _Nonnull, size_t, off_t, size_t) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 ssize_t __pread_real(int, void* _Nonnull, size_t, off_t) __RENAME(pread);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 ssize_t __pread64_chk(int, void* _Nonnull, size_t, off64_t, size_t) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 ssize_t __pread64_real(int, void* _Nonnull, size_t, off64_t) __RENAME(pread64);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 ssize_t __pwrite_chk(int, const void* _Nonnull, size_t, off_t, size_t) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 ssize_t __pwrite_real(int, const void* _Nonnull, size_t, off_t) __RENAME(pwrite);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 ssize_t __pwrite64_chk(int, const void* _Nonnull, size_t, off64_t, size_t) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 ssize_t __pwrite64_real(int, const void* _Nonnull, size_t, off64_t) __RENAME(pwrite64);
 
 ssize_t __read_chk(int, void* __BIONIC_COMPLICATED_NULLNESS, size_t, size_t);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 ssize_t __write_chk(int, const void* __BIONIC_COMPLICATED_NULLNESS, size_t, size_t) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 ssize_t __readlink_chk(const char* _Nonnull, char* _Nonnull, size_t, size_t) __INTRODUCED_IN(23);
 ssize_t __readlinkat_chk(int dirfd, const char* _Nonnull, char* _Nonnull, size_t, size_t) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 #if defined(__BIONIC_FORTIFY)
 
diff --git a/libc/include/bits/getentropy.h b/libc/include/bits/getentropy.h
index 98d8879..c878470 100644
--- a/libc/include/bits/getentropy.h
+++ b/libc/include/bits/getentropy.h
@@ -48,6 +48,10 @@
  *
  * See also arc4random_buf() which is available in all API levels.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 __nodiscard int getentropy(void* _Nonnull __buffer, size_t __buffer_size) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/bits/lockf.h b/libc/include/bits/lockf.h
index 195b34a..8f922b9 100644
--- a/libc/include/bits/lockf.h
+++ b/libc/include/bits/lockf.h
@@ -56,6 +56,8 @@
  *
  * See also flock().
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int lockf(int __fd, int __op, off_t __length) __RENAME_IF_FILE_OFFSET64(lockf64) __INTRODUCED_IN(24);
 
 /**
@@ -63,5 +65,7 @@
  * even from a 32-bit process without `_FILE_OFFSET_BITS=64`.
  */
 int lockf64(int __fd, int __op, off64_t __length) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 __END_DECLS
diff --git a/libc/include/bits/seek_constants.h b/libc/include/bits/seek_constants.h
index bfc02a8..a4fffb2 100644
--- a/libc/include/bits/seek_constants.h
+++ b/libc/include/bits/seek_constants.h
@@ -33,6 +33,8 @@
  * @brief The `SEEK_` constants.
  */
 
+#include <sys/cdefs.h>
+
 /** Seek to an absolute offset. */
 #define SEEK_SET 0
 /** Seek relative to the current offset. */
diff --git a/libc/include/bits/stdatomic.h b/libc/include/bits/stdatomic.h
index c74eafd..ebdc9e5 100644
--- a/libc/include/bits/stdatomic.h
+++ b/libc/include/bits/stdatomic.h
@@ -134,6 +134,8 @@
 	memory_order_seq_cst = __ATOMIC_SEQ_CST
 } memory_order;
 
+#define kill_dependency(y) (y)
+
 /*
  * 7.17.4 Fences.
  */
diff --git a/libc/include/bits/stdlib_inlines.h b/libc/include/bits/stdlib_inlines.h
new file mode 100644
index 0000000..fffca19
--- /dev/null
+++ b/libc/include/bits/stdlib_inlines.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <xlocale.h>
+#include <sys/cdefs.h>
+
+#if !defined(__BIONIC_STDLIB_INLINE)
+#define __BIONIC_STDLIB_INLINE static __inline
+#endif
+
+__BEGIN_DECLS
+
+__BIONIC_STDLIB_INLINE double strtod_l(const char* _Nonnull __s, char* _Nullable * _Nullable __end_ptr, locale_t _Nonnull __l) {
+  return strtod(__s, __end_ptr);
+}
+
+__BIONIC_STDLIB_INLINE float strtof_l(const char* _Nonnull __s, char* _Nullable * _Nullable __end_ptr, locale_t _Nonnull __l) {
+  return strtof(__s, __end_ptr);
+}
+
+__END_DECLS
diff --git a/libc/include/bits/strcasecmp.h b/libc/include/bits/strcasecmp.h
index be910ad..d76cec9 100644
--- a/libc/include/bits/strcasecmp.h
+++ b/libc/include/bits/strcasecmp.h
@@ -51,7 +51,11 @@
 /**
  * Like strcasecmp() but taking a `locale_t`.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int strcasecmp_l(const char* _Nonnull __s1, const char* _Nonnull __s2, locale_t _Nonnull __l) __attribute_pure__ __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [strncasecmp(3)](https://man7.org/linux/man-pages/man3/strncasecmp.3.html) compares the first
@@ -66,6 +70,10 @@
 /**
  * Like strncasecmp() but taking a `locale_t`.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int strncasecmp_l(const char* _Nonnull __s1, const char* _Nonnull __s2, size_t __n, locale_t _Nonnull __l) __attribute_pure__ __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/bits/swab.h b/libc/include/bits/swab.h
index 9591c2e..da2865a 100644
--- a/libc/include/bits/swab.h
+++ b/libc/include/bits/swab.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 #if !defined(__BIONIC_SWAB_INLINE)
diff --git a/libc/include/bits/termios_inlines.h b/libc/include/bits/termios_inlines.h
index a884b59..bb04e4d 100644
--- a/libc/include/bits/termios_inlines.h
+++ b/libc/include/bits/termios_inlines.h
@@ -29,8 +29,9 @@
 #ifndef _BITS_TERMIOS_INLINES_H_
 #define _BITS_TERMIOS_INLINES_H_
 
-#include <errno.h>
 #include <sys/cdefs.h>
+
+#include <errno.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 
diff --git a/libc/include/bits/termios_winsize_inlines.h b/libc/include/bits/termios_winsize_inlines.h
index ae246e4..86777b0 100644
--- a/libc/include/bits/termios_winsize_inlines.h
+++ b/libc/include/bits/termios_winsize_inlines.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <errno.h>
 #include <sys/cdefs.h>
+
+#include <errno.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 
diff --git a/libc/include/bits/threads_inlines.h b/libc/include/bits/threads_inlines.h
index 05b785a..ab294c1 100644
--- a/libc/include/bits/threads_inlines.h
+++ b/libc/include/bits/threads_inlines.h
@@ -28,6 +28,8 @@
 
 #pragma once
 
+#include <sys/cdefs.h>
+
 #include <threads.h>
 
 #include <errno.h>
diff --git a/libc/include/bits/wctype.h b/libc/include/bits/wctype.h
index 13a4254..d0cffec 100644
--- a/libc/include/bits/wctype.h
+++ b/libc/include/bits/wctype.h
@@ -58,8 +58,12 @@
 int iswctype(wint_t __wc, wctype_t __type);
 
 typedef const void* wctrans_t;
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 wint_t towctrans(wint_t __wc, wctrans_t _Nonnull __transform) __INTRODUCED_IN(26);
 wctrans_t _Nullable wctrans(const char* _Nonnull __name) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
 
diff --git a/libc/include/complex.h b/libc/include/complex.h
index f205abd..1115862 100644
--- a/libc/include/complex.h
+++ b/libc/include/complex.h
@@ -53,76 +53,190 @@
 
 /* 7.3.5 Trigonometric functions */
 /* 7.3.5.1 The cacos functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex cacos(double complex __z) __INTRODUCED_IN(23);
 float complex cacosf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex cacosl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.5.2 The casin functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex casin(double complex __z) __INTRODUCED_IN(23);
 float complex casinf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex casinl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.5.1 The catan functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex catan(double complex __z) __INTRODUCED_IN(23);
 float complex catanf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex catanl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.5.1 The ccos functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex ccos(double complex __z) __INTRODUCED_IN(23);
 float complex ccosf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex ccosl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.5.1 The csin functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex csin(double complex __z) __INTRODUCED_IN(23);
 float complex csinf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex csinl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.5.1 The ctan functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex ctan(double complex __z) __INTRODUCED_IN(23);
 float complex ctanf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex ctanl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /* 7.3.6 Hyperbolic functions */
 /* 7.3.6.1 The cacosh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex cacosh(double complex __z) __INTRODUCED_IN(23);
 float complex cacoshf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex cacoshl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.6.2 The casinh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex casinh(double complex __z) __INTRODUCED_IN(23);
 float complex casinhf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex casinhl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.6.3 The catanh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex catanh(double complex __z) __INTRODUCED_IN(23);
 float complex catanhf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex catanhl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.6.4 The ccosh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex ccosh(double complex __z) __INTRODUCED_IN(23);
 float complex ccoshf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex ccoshl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.6.5 The csinh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex csinh(double complex __z) __INTRODUCED_IN(23);
 float complex csinhf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex csinhl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.6.6 The ctanh functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex ctanh(double complex __z) __INTRODUCED_IN(23);
 float complex ctanhf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex ctanhl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /* 7.3.7 Exponential and logarithmic functions */
 /* 7.3.7.1 The cexp functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex cexp(double complex __z) __INTRODUCED_IN(23);
 float complex cexpf(float complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 long double complex cexpl(long double complex __z) __INTRODUCED_IN(26);
 /* 7.3.7.2 The clog functions */
 double complex clog(double complex __z) __INTRODUCED_IN(26);
 float complex clogf(float complex __z) __INTRODUCED_IN(26);
 long double complex clogl(long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /* 7.3.8 Power and absolute-value functions */
 /* 7.3.8.1 The cabs functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double cabs(double complex __z) __INTRODUCED_IN(23);
 float cabsf(float complex __z) __INTRODUCED_IN(23);
 long double cabsl(long double complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 /* 7.3.8.2 The cpow functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 double complex cpow(double complex __x, double complex __z) __INTRODUCED_IN(26);
 float complex cpowf(float complex __x, float complex __z) __INTRODUCED_IN(26);
 long double complex cpowl(long double complex __x, long double complex __z) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 /* 7.3.8.3 The csqrt functions */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 double complex csqrt(double complex __z) __INTRODUCED_IN(23);
 float complex csqrtf(float complex __z) __INTRODUCED_IN(23);
 long double complex csqrtl(long double complex __z) __INTRODUCED_IN(23);
@@ -148,6 +262,8 @@
 double creal(double complex __z) __INTRODUCED_IN(23);
 float crealf(float complex __z) __INTRODUCED_IN(23);
 long double creall(long double complex __z) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
 
diff --git a/libc/include/ctype.h b/libc/include/ctype.h
index cb926a4..dc3f673 100644
--- a/libc/include/ctype.h
+++ b/libc/include/ctype.h
@@ -95,7 +95,7 @@
 
 /** Internal implementation detail. Do not use. */
 __attribute__((__no_sanitize__("unsigned-integer-overflow")))
-static inline int __bionic_ctype_in_range(unsigned __lo, int __ch, unsigned __hi) {
+__BIONIC_CTYPE_INLINE int __bionic_ctype_in_range(unsigned __lo, int __ch, unsigned __hi) {
   return (__BIONIC_CAST(static_cast, unsigned, __ch) - __lo) < (__hi - __lo + 1);
 }
 
diff --git a/libc/include/dirent.h b/libc/include/dirent.h
index 5333d78..8058cfb 100644
--- a/libc/include/dirent.h
+++ b/libc/include/dirent.h
@@ -33,8 +33,9 @@
  * @brief Directory entry iteration.
  */
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
@@ -149,6 +150,8 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void seekdir(DIR* _Nonnull __dir, long __location) __INTRODUCED_IN(23);
 
 /**
@@ -161,6 +164,8 @@
  * Available since API level 23.
  */
 long telldir(DIR* _Nonnull __dir) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [dirfd(3)](https://man7.org/linux/man-pages/man3/dirfd.3.html)
@@ -221,6 +226,8 @@
  *
  * Available since API level 24.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int scandirat64(int __dir_fd, const char* _Nonnull __path, struct dirent64* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent64* _Nonnull), int (* _Nullable __comparator)(const struct dirent64* _Nonnull * _Nonnull, const struct dirent64* _Nonnull * _Nonnull)) __INTRODUCED_IN(24);
 
 /**
@@ -237,6 +244,8 @@
  * Available since API level 24.
  */
 int scandirat(int __dir_fd, const char* _Nonnull __path, struct dirent* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent* _Nonnull), int (* _Nullable __comparator)(const struct dirent* _Nonnull * _Nonnull, const struct dirent* _Nonnull * _Nonnull)) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 #endif
 
diff --git a/libc/include/dlfcn.h b/libc/include/dlfcn.h
index 071d50a..67759b8 100644
--- a/libc/include/dlfcn.h
+++ b/libc/include/dlfcn.h
@@ -28,9 +28,10 @@
 
 #pragma once
 
-#include <stdint.h>
 #include <sys/cdefs.h>
 
+#include <stdint.h>
+
 __BEGIN_DECLS
 
 /**
@@ -116,7 +117,11 @@
  * Returns the address of the symbol on success, and returns NULL on failure,
  * in which case dlerror() can be used to retrieve the specific error.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 void* _Nullable dlvsym(void* __BIONIC_COMPLICATED_NULLNESS __handle, const char* _Nullable __symbol, const char* _Nullable __version) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 /**
  * [dladdr(3)](https://man7.org/linux/man-pages/man3/dladdr.3.html)
diff --git a/libc/include/err.h b/libc/include/err.h
index d8122d7..4a1841b 100644
--- a/libc/include/err.h
+++ b/libc/include/err.h
@@ -36,8 +36,9 @@
  * @brief BSD error reporting functions. See `<error.h>` for the GNU equivalent.
  */
 
-#include <stdarg.h>
 #include <sys/cdefs.h>
+
+#include <stdarg.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/error.h b/libc/include/error.h
index cb867cd..a9bdc24 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -44,6 +44,8 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 extern void (* _Nullable error_print_progname)(void) __INTRODUCED_IN(23);
 
 /**
@@ -81,5 +83,7 @@
  * Available since API level 23.
  */
 void error_at_line(int __status, int __errno, const char* _Nonnull __filename, unsigned int __line_number, const char* _Nonnull __fmt, ...) __printflike(5, 6) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/execinfo.h b/libc/include/execinfo.h
index 88f4ae7..84b637c 100644
--- a/libc/include/execinfo.h
+++ b/libc/include/execinfo.h
@@ -47,6 +47,8 @@
  *
  * Available since API level 33.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(33)
 int backtrace(void* _Nonnull * _Nonnull buffer, int size) __INTRODUCED_IN(33);
 
 /**
@@ -70,5 +72,7 @@
  * Available since API level 33.
  */
 void backtrace_symbols_fd(void* _Nonnull const* _Nonnull buffer, int size, int fd) __INTRODUCED_IN(33);
+#endif /* __BIONIC_AVAILABILITY_GUARD(33) */
+
 
 __END_DECLS
diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index 1e9a285..2bd1fc6 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -227,7 +227,11 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int sync_file_range(int __fd, off64_t __offset, off64_t __length, unsigned int __flags) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 #endif
 
diff --git a/libc/include/glob.h b/libc/include/glob.h
index 2c2b8d1..ccdf2e9 100644
--- a/libc/include/glob.h
+++ b/libc/include/glob.h
@@ -92,8 +92,12 @@
 
 __BEGIN_DECLS
 
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int glob(const char* _Nonnull __pattern, int __flags, int (* _Nullable __error_callback)(const char* _Nonnull __failure_path, int __failure_errno), glob_t* _Nonnull __result_ptr) __INTRODUCED_IN(28);
 void globfree(glob_t* _Nonnull __result_ptr) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
 
diff --git a/libc/include/grp.h b/libc/include/grp.h
index 2451db5..a48c046 100644
--- a/libc/include/grp.h
+++ b/libc/include/grp.h
@@ -51,12 +51,20 @@
 struct group* _Nullable getgrnam(const char* _Nonnull __name);
 
 /* Note: Android has thousands and thousands of ids to iterate through. */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 struct group* _Nullable getgrent(void) __INTRODUCED_IN(26);
 
 void setgrent(void) __INTRODUCED_IN(26);
 void endgrent(void) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int getgrgid_r(gid_t __gid, struct group* __BIONIC_COMPLICATED_NULLNESS __group, char* _Nonnull __buf, size_t __n, struct group* _Nullable * _Nonnull __result) __INTRODUCED_IN(24);
 int getgrnam_r(const char* _Nonnull __name, struct group* __BIONIC_COMPLICATED_NULLNESS __group, char* _Nonnull __buf, size_t __n, struct group* _Nullable *_Nonnull __result) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 int getgrouplist(const char* _Nonnull __user, gid_t __group, gid_t* __BIONIC_COMPLICATED_NULLNESS __groups, int* _Nonnull __group_count);
 int initgroups(const char* _Nonnull __user, gid_t __group);
 
diff --git a/libc/include/iconv.h b/libc/include/iconv.h
index 9da46b4..35328ee 100644
--- a/libc/include/iconv.h
+++ b/libc/include/iconv.h
@@ -60,6 +60,8 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 iconv_t _Nonnull iconv_open(const char* _Nonnull __dst_encoding, const char* _Nonnull __src_encoding) __INTRODUCED_IN(28);
 
 /**
@@ -82,5 +84,7 @@
  * Available since API level 28.
  */
 int iconv_close(iconv_t _Nonnull __converter) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/ifaddrs.h b/libc/include/ifaddrs.h
index c4d0e10..87d2947 100644
--- a/libc/include/ifaddrs.h
+++ b/libc/include/ifaddrs.h
@@ -80,6 +80,8 @@
  *
  * Available since API level 24.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int getifaddrs(struct ifaddrs* _Nullable * _Nonnull __list_ptr) __INTRODUCED_IN(24);
 
 /**
@@ -89,5 +91,7 @@
  * Available since API level 24.
  */
 void freeifaddrs(struct ifaddrs* _Nullable __ptr) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 __END_DECLS
diff --git a/libc/include/inttypes.h b/libc/include/inttypes.h
index 9fcd9f3..790030e 100644
--- a/libc/include/inttypes.h
+++ b/libc/include/inttypes.h
@@ -19,8 +19,8 @@
 #ifndef	_INTTYPES_H_
 #define	_INTTYPES_H_
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+#include <stdint.h>
 
 #ifdef __LP64__
 #define __PRI_64_prefix  "l"
diff --git a/libc/include/langinfo.h b/libc/include/langinfo.h
index 2b43892..b9d695c 100644
--- a/libc/include/langinfo.h
+++ b/libc/include/langinfo.h
@@ -92,8 +92,12 @@
 #define NOEXPR 54
 #define CRNCYSTR 55
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 char* _Nonnull nl_langinfo(nl_item __item) __INTRODUCED_IN(26);
 char* _Nonnull nl_langinfo_l(nl_item __item, locale_t _Nonnull __l) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
 
diff --git a/libc/include/limits.h b/libc/include/limits.h
index e1f566c..5e9ce59 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -1,6 +1,3 @@
-/*	$OpenBSD: limits.h,v 1.13 2005/12/31 19:29:38 millert Exp $	*/
-/*	$NetBSD: limits.h,v 1.7 1994/10/26 00:56:00 cgd Exp $	*/
-
 /*
  * Copyright (c) 1988 The Regents of the University of California.
  * All rights reserved.
@@ -32,108 +29,101 @@
  *	@(#)limits.h	5.9 (Berkeley) 4/3/91
  */
 
-#ifndef _LIMITS_H_
-#define _LIMITS_H_
+#pragma once
+
+/**
+ * @file limits.h
+ * @brief Constants relating to implementation limits.
+ *
+ * This file is included via `#include_next` from the clang header of the same
+ * name that provides all the limits that the compiler is responsible for,
+ * primarily those relating to integer types defined by the C standard.
+ * This file defines the additional limits defined by POSIX.
+ */
+
+/*
+ * The Android build system has bionic _before_ the clang headers,
+ * so although the claim above that clang does an `#include_next`
+ * of this file is true for the NDK, it's not true for the OS,
+ * and we need to paper over that difference here until/unless
+ * the OS build changes.
+ */
+#if __has_include_next(<limits.h>)
+#include_next <limits.h>
+#endif
 
 #include <sys/cdefs.h>
 
 /* Historically bionic exposed the content of <float.h> from <limits.h> and <sys/limits.h> too. */
 #include <float.h>
 
+/* Many of the POSIX limits come from the kernel. */
 #include <linux/limits.h>
 
-#define PASS_MAX		128	/* _PASSWORD_LEN from <pwd.h> */
-
-#define NL_ARGMAX		9
-#define NL_LANGMAX		14
-#define NL_MSGMAX		32767
-#define NL_NMAX			1
-#define NL_SETMAX		255
-#define NL_TEXTMAX		255
-
-#define TMP_MAX                 308915776
-
-/* TODO: get all these from the compiler's <limits.h>? */
-
-#define CHAR_BIT 8
-#ifdef __LP64__
-# define LONG_BIT 64
-#else
-# define LONG_BIT 32
+/*
+ * bionic always exposed these alternative names,
+ * but clang's <limits.h> considers them GNU extensions,
+ * and may or may not have defined them.
+ */
+#ifndef LONG_LONG_MIN
+/** Non-portable synonym; use LLONG_MIN directly instead. */
+#define LONG_LONG_MIN LLONG_MIN
 #endif
+#ifndef LONG_LONG_MAX
+/** Non-portable synonym; use LLONG_MAX directly instead. */
+#define LONG_LONG_MAX LLONG_MAX
+#endif
+#ifndef ULONG_LONG_MAX
+/** Non-portable synonym; use ULLONG_MAX directly instead. */
+#define ULONG_LONG_MAX ULLONG_MAX
+#endif
+
+/** Maximum number of positional arguments in a printf()/scanf() format string. */
+#define NL_ARGMAX 9
+/** Maximum number of bytes in a $LANG name. */
+#define NL_LANGMAX 14
+/** Irrelevant with Android's <nl_types.h>. */
+#define NL_MSGMAX 32767
+/** Obsolete; removed from POSIX. */
+#define NL_NMAX 1
+/** Irrelevant with Android's <nl_types.h>. */
+#define NL_SETMAX 255
+/** Irrelevant with Android's <nl_types.h>. */
+#define NL_TEXTMAX 255
+
+/** Obsolete; removed from POSIX. */
+#define PASS_MAX 128
+/** Obsolete; removed from POSIX. */
+#define TMP_MAX 308915776
+
+/** Number of bits in a `long` (POSIX). */
+#if __LP64__
+#define LONG_BIT 64
+#else
+#define LONG_BIT 32
+#endif
+/** Number of bits in a "word" of `int` (POSIX). */
 #define WORD_BIT 32
 
-#define	SCHAR_MAX	0x7f		/* max value for a signed char */
-#define SCHAR_MIN	(-0x7f-1)	/* min value for a signed char */
-
-#define	UCHAR_MAX	0xffU		/* max value for an unsigned char */
-#ifdef __CHAR_UNSIGNED__
-# define CHAR_MIN	0		/* min value for a char */
-# define CHAR_MAX	0xff		/* max value for a char */
-#else
-# define CHAR_MAX	0x7f
-# define CHAR_MIN	(-0x7f-1)
-#endif
-
-#define	USHRT_MAX	0xffffU		/* max value for an unsigned short */
-#define	SHRT_MAX	0x7fff		/* max value for a short */
-#define SHRT_MIN        (-0x7fff-1)     /* min value for a short */
-
-#define	UINT_MAX	0xffffffffU	/* max value for an unsigned int */
-#define	INT_MAX		0x7fffffff	/* max value for an int */
-#define	INT_MIN		(-0x7fffffff-1)	/* min value for an int */
-
-#ifdef __LP64__
-# define ULONG_MAX	0xffffffffffffffffUL     /* max value for unsigned long */
-# define LONG_MAX	0x7fffffffffffffffL      /* max value for a signed long */
-# define LONG_MIN	(-0x7fffffffffffffffL-1) /* min value for a signed long */
-#else
-# define ULONG_MAX	0xffffffffUL	/* max value for an unsigned long */
-# define LONG_MAX	0x7fffffffL	/* max value for a long */
-# define LONG_MIN	(-0x7fffffffL-1)/* min value for a long */
-#endif
-
-# define ULLONG_MAX	0xffffffffffffffffULL     /* max value for unsigned long long */
-# define LLONG_MAX	0x7fffffffffffffffLL      /* max value for a signed long long */
-# define LLONG_MIN	(-0x7fffffffffffffffLL-1) /* min value for a signed long long */
-
-/* GLibc compatibility definitions.
-   Note that these are defined by GCC's <limits.h>
-   only when __GNU_LIBRARY__ is defined, i.e. when
-   targetting GLibc. */
-#ifndef LONG_LONG_MIN
-#define LONG_LONG_MIN  LLONG_MIN
-#endif
-
-#ifndef LONG_LONG_MAX
-#define LONG_LONG_MAX  LLONG_MAX
-#endif
-
-#ifndef ULONG_LONG_MAX
-#define ULONG_LONG_MAX  ULLONG_MAX
-#endif
-
-#if defined(__USE_BSD) || defined(__BIONIC__) /* Historically bionic exposed these. */
-# define UID_MAX	UINT_MAX	/* max value for a uid_t */
-# define GID_MAX	UINT_MAX	/* max value for a gid_t */
-#if defined(__LP64__)
+/** Maximum value of a uid_t. */
+#define UID_MAX UINT_MAX
+/** Maximum value of a gid_t. */
+#define GID_MAX UINT_MAX
+/** Maximum value of a size_t. */
 #define SIZE_T_MAX ULONG_MAX
-#else
-#define SIZE_T_MAX UINT_MAX
-#endif
-#endif
-
-#if defined(__LP64__)
+/** Maximum value of a ssize_t. */
 #define SSIZE_MAX LONG_MAX
-#else
-#define SSIZE_MAX INT_MAX
-#endif
 
+/** Maximum number of bytes in a multibyte character. */
 #define MB_LEN_MAX 4
 
+/** Default process priority. */
 #define NZERO 20
 
+/** Maximum number of struct iovec that can be passed in a single readv()/writev(). */
 #define IOV_MAX 1024
+
+/** Maximum value for a semaphore. */
 #define SEM_VALUE_MAX 0x3fffffff
 
 /** Do not use: prefer getline() or asprintf() rather than hard-coding an arbitrary size. */
@@ -142,12 +132,17 @@
 /* POSIX says these belong in <unistd.h> but BSD has some in <limits.h>. */
 #include <bits/posix_limits.h>
 
+/** Maximum length of a hostname returned by gethostname(). */
 #define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
+
+/** Maximum length of a login name. */
 #define LOGIN_NAME_MAX 256
+
+/** Maximum length of terminal device name. */
 #define TTY_NAME_MAX 32
 
-/* >= _POSIX_THREAD_DESTRUCTOR_ITERATIONS */
-#define PTHREAD_DESTRUCTOR_ITERATIONS 4
+/** Maximum number of attempts to destroy thread-specific data when a thread exits. */
+#define PTHREAD_DESTRUCTOR_ITERATIONS _POSIX_THREAD_DESTRUCTOR_ITERATIONS
 
 /**
  * The number of calls to pthread_key_create() without intervening calls to
@@ -156,7 +151,5 @@
  */
 #define PTHREAD_KEYS_MAX 128
 
-/** bionic has no specific limit on the number of threads. */
+/** bionic has no fixed limit on the number of threads. */
 #undef PTHREAD_THREADS_MAX
-
-#endif /* !_LIMITS_H_ */
diff --git a/libc/include/link.h b/libc/include/link.h
index 216502e..331070e 100644
--- a/libc/include/link.h
+++ b/libc/include/link.h
@@ -33,8 +33,9 @@
  * @brief Extra dynamic linker functionality (see also <dlfcn.h>).
  */
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 #include <elf.h>
diff --git a/libc/include/malloc.h b/libc/include/malloc.h
index 2fa4b49..dc2ca2b 100644
--- a/libc/include/malloc.h
+++ b/libc/include/malloc.h
@@ -195,7 +195,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int malloc_info(int __must_be_zero, FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * mallopt() option to set the decay time. Valid values are -1, 0 and 1.
@@ -368,7 +372,11 @@
  *
  * Available since API level 26.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int mallopt(int __option, int __value) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /**
  * [__malloc_hook(3)](https://man7.org/linux/man-pages/man3/__malloc_hook.3.html)
@@ -379,6 +387,8 @@
  *
  * See also: [extra documentation](https://android.googlesource.com/platform/bionic/+/main/libc/malloc_hooks/README.md)
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 extern void* _Nonnull (*volatile _Nonnull __malloc_hook)(size_t __byte_count, const void* _Nonnull __caller) __INTRODUCED_IN(28);
 
 /**
@@ -413,5 +423,7 @@
  * See also: [extra documentation](https://android.googlesource.com/platform/bionic/+/main/libc/malloc_hooks/README.md)
  */
 extern void* _Nonnull (*volatile _Nonnull __memalign_hook)(size_t __alignment, size_t __byte_count, const void* _Nonnull __caller) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/math.h b/libc/include/math.h
index 343ab98..59161bf 100644
--- a/libc/include/math.h
+++ b/libc/include/math.h
@@ -350,7 +350,11 @@
 double gamma_r(double __x, int* _Nonnull __sign);
 double lgamma_r(double __x, int* _Nonnull __sign);
 double significand(double __x);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 long double lgammal_r(long double __x, int* _Nonnull __sign) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 long double significandl(long double __x);
 float dremf(float __x, float __y);
 int finitef(float __x) __attribute_const__;
diff --git a/libc/include/mntent.h b/libc/include/mntent.h
index 9a31838..4c03602 100644
--- a/libc/include/mntent.h
+++ b/libc/include/mntent.h
@@ -29,8 +29,9 @@
 #ifndef _MNTENT_H_
 #define _MNTENT_H_
 
-#include <stdio.h>
 #include <sys/cdefs.h>
+
+#include <stdio.h>
 #include <paths.h>  /* for _PATH_MOUNTED */
 
 #define MOUNTED _PATH_MOUNTED
@@ -61,7 +62,11 @@
 struct mntent* _Nullable getmntent(FILE* _Nonnull __fp);
 struct mntent* _Nullable getmntent_r(FILE* _Nonnull __fp, struct mntent* _Nonnull __entry, char* _Nonnull __buf, int __size);
 FILE* _Nullable setmntent(const char* _Nonnull __filename, const char* _Nonnull __type);
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 char* _Nullable hasmntopt(const struct mntent* _Nonnull __entry, const char* _Nonnull __option) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
 
diff --git a/libc/include/net/if.h b/libc/include/net/if.h
index 79b4195..50bc74c 100644
--- a/libc/include/net/if.h
+++ b/libc/include/net/if.h
@@ -29,9 +29,10 @@
 #ifndef _NET_IF_H_
 #define _NET_IF_H_
 
+#include <sys/cdefs.h>
+
 #include <sys/socket.h>
 #include <linux/if.h>
-#include <sys/cdefs.h>
 
 #ifndef IF_NAMESIZE
 #define IF_NAMESIZE IFNAMSIZ
@@ -46,8 +47,12 @@
 
 char* _Nullable if_indextoname(unsigned __index, char* _Nonnull __buf);
 unsigned if_nametoindex(const char* _Nonnull __name);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 struct if_nameindex* _Nullable if_nameindex(void) __INTRODUCED_IN(24);
 void if_freenameindex(struct if_nameindex* _Nullable __ptr) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 __END_DECLS
 
diff --git a/libc/include/netdb.h b/libc/include/netdb.h
index 88214d5..04aaf5c 100644
--- a/libc/include/netdb.h
+++ b/libc/include/netdb.h
@@ -212,28 +212,52 @@
 void herror(const char* _Nonnull __s);
 const char* _Nonnull hstrerror(int __error);
 struct hostent* _Nullable gethostbyaddr(const void* _Nonnull __addr, socklen_t __length, int __type);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int gethostbyaddr_r(const void* _Nonnull __addr, socklen_t __length, int __type, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 struct hostent* _Nullable gethostbyname(const char* _Nonnull __name);
 int gethostbyname_r(const char* _Nonnull __name, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr);
 struct hostent* _Nullable gethostbyname2(const char* _Nonnull __name, int __af);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int gethostbyname2_r(const char* _Nonnull __name, int __af, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 void endhostent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct hostent* _Nullable gethostent(void);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 void sethostent(int __stay_open) __INTRODUCED_IN(28);
 
 /* These functions are obsolete. None of these functions return anything but nullptr. */
 void endnetent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct netent* _Nullable getnetbyaddr(uint32_t __net, int __type);
 struct netent* _Nullable getnetbyname(const char* _Nonnull __name);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 struct netent* _Nullable getnetent(void) __INTRODUCED_IN(28);
 void setnetent(int __stay_open) __INTRODUCED_IN(28);
 
 /* None of these functions return anything but nullptr. */
 void endprotoent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct protoent* _Nullable getprotobyname(const char* _Nonnull __name);
 struct protoent* _Nullable getprotobynumber(int __proto);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 struct protoent* _Nullable getprotoent(void) __INTRODUCED_IN(28);
 void setprotoent(int __stay_open) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /* These functions return entries from a built-in database. */
 void endservent(void);
diff --git a/libc/include/netinet/icmp6.h b/libc/include/netinet/icmp6.h
index 2b237a8..ebd9f6c 100644
--- a/libc/include/netinet/icmp6.h
+++ b/libc/include/netinet/icmp6.h
@@ -65,9 +65,10 @@
 #ifndef _NETINET_ICMP6_H_
 #define _NETINET_ICMP6_H_
 
-#include <netinet/in.h> /* android-added: glibc source compatibility. */
 #include <sys/cdefs.h>
 
+#include <netinet/in.h> /* android-added: glibc source compatibility. */
+
 #define ICMPV6_PLD_MAXLEN	1232	/* IPV6_MMTU - sizeof(struct ip6_hdr)
 					   - sizeof(struct icmp6_hdr) */
 
diff --git a/libc/include/netinet/in.h b/libc/include/netinet/in.h
index 163e614..d4ce302 100644
--- a/libc/include/netinet/in.h
+++ b/libc/include/netinet/in.h
@@ -28,9 +28,10 @@
 
 #pragma once
 
+#include <sys/cdefs.h>
+
 #include <endian.h>
 #include <netinet/in6.h>
-#include <sys/cdefs.h>
 #include <sys/socket.h>
 
 #include <linux/in.h>
diff --git a/libc/include/nl_types.h b/libc/include/nl_types.h
index 6c9935d..172d80d 100644
--- a/libc/include/nl_types.h
+++ b/libc/include/nl_types.h
@@ -62,6 +62,8 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 nl_catd _Nonnull catopen(const char* _Nonnull __name, int __flag) __INTRODUCED_IN(26);
 
 /**
@@ -80,5 +82,7 @@
  * On Android, this always returns -1 with `errno` set to `EBADF`.
  */
 int catclose(nl_catd _Nonnull __catalog) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
diff --git a/libc/include/poll.h b/libc/include/poll.h
index 0dda3da..e57f812 100644
--- a/libc/include/poll.h
+++ b/libc/include/poll.h
@@ -64,7 +64,11 @@
 /**
  * Like ppoll() but allows setting a signal mask with RT signals even from a 32-bit process.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int ppoll64(struct pollfd* _Nullable  __fds, nfds_t __count, const struct timespec* _Nullable __timeout, const sigset64_t* _Nullable __mask) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 #if defined(__BIONIC_INCLUDE_FORTIFY_HEADERS)
 #define _POLL_H_
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index d718b40..8b78a74 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -33,11 +33,12 @@
  * @brief POSIX threads.
  */
 
+#include <sys/cdefs.h>
+
 #include <limits.h>
 #include <bits/page_size.h>
 #include <bits/pthread_types.h>
 #include <sched.h>
-#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <time.h>
 
@@ -98,7 +99,11 @@
 int pthread_attr_destroy(pthread_attr_t* _Nonnull __attr);
 int pthread_attr_getdetachstate(const pthread_attr_t* _Nonnull __attr, int* _Nonnull __state);
 int pthread_attr_getguardsize(const pthread_attr_t* _Nonnull __attr, size_t* _Nonnull __size);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_attr_getinheritsched(const pthread_attr_t* _Nonnull __attr, int* _Nonnull __flag) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_attr_getschedparam(const pthread_attr_t* _Nonnull __attr, struct sched_param* _Nonnull __param);
 int pthread_attr_getschedpolicy(const pthread_attr_t* _Nonnull __attr, int* _Nonnull __policy);
 int pthread_attr_getscope(const pthread_attr_t* _Nonnull __attr, int* _Nonnull __scope);
@@ -107,7 +112,11 @@
 int pthread_attr_init(pthread_attr_t* _Nonnull __attr);
 int pthread_attr_setdetachstate(pthread_attr_t* _Nonnull __attr, int __state);
 int pthread_attr_setguardsize(pthread_attr_t* _Nonnull __attr, size_t __size);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_attr_setinheritsched(pthread_attr_t* _Nonnull __attr, int __flag) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_attr_setschedparam(pthread_attr_t* _Nonnull __attr, const struct sched_param* _Nonnull __param);
 int pthread_attr_setschedpolicy(pthread_attr_t* _Nonnull __attr, int __policy);
 int pthread_attr_setscope(pthread_attr_t* _Nonnull __attr, int __scope);
@@ -122,8 +131,12 @@
 int pthread_condattr_setpshared(pthread_condattr_t* _Nonnull __attr, int __shared);
 
 int pthread_cond_broadcast(pthread_cond_t* _Nonnull __cond);
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int pthread_cond_clockwait(pthread_cond_t* _Nonnull __cond, pthread_mutex_t* _Nonnull __mutex, clockid_t __clock,
                            const struct timespec* _Nullable __timeout) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 int pthread_cond_destroy(pthread_cond_t* _Nonnull __cond);
 int pthread_cond_init(pthread_cond_t* _Nonnull __cond, const pthread_condattr_t* _Nullable __attr);
 int pthread_cond_signal(pthread_cond_t* _Nonnull __cond);
@@ -138,8 +151,12 @@
  * Note that pthread_cond_clockwait() allows specifying an arbitrary clock and has superseded this
  * function.
  */
+
+#if (!defined(__LP64__)) || (defined(__LP64__) && __ANDROID_API__ >= 28)
 int pthread_cond_timedwait_monotonic_np(pthread_cond_t* _Nonnull __cond, pthread_mutex_t* _Nonnull __mutex,
                                         const struct timespec* _Nullable __timeout) __INTRODUCED_IN_64(28);
+#endif /* (!defined(__LP64__)) || (defined(__LP64__) && __ANDROID_API__ >= 28) */
+
 int pthread_cond_wait(pthread_cond_t* _Nonnull __cond, pthread_mutex_t* _Nonnull __mutex);
 
 int pthread_create(pthread_t* _Nonnull __pthread_ptr, pthread_attr_t const* _Nullable __attr, void* _Nullable (* _Nonnull __start_routine)(void* _Nullable), void* _Nullable);
@@ -187,14 +204,26 @@
 int pthread_mutexattr_destroy(pthread_mutexattr_t* _Nonnull __attr);
 int pthread_mutexattr_getpshared(const pthread_mutexattr_t* _Nonnull __attr, int* _Nonnull __shared);
 int pthread_mutexattr_gettype(const pthread_mutexattr_t* _Nonnull __attr, int* _Nonnull __type);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_mutexattr_getprotocol(const pthread_mutexattr_t* _Nonnull __attr, int* _Nonnull __protocol) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_mutexattr_init(pthread_mutexattr_t* _Nonnull __attr);
 int pthread_mutexattr_setpshared(pthread_mutexattr_t* _Nonnull __attr, int __shared);
 int pthread_mutexattr_settype(pthread_mutexattr_t* _Nonnull __attr, int __type);
-int pthread_mutexattr_setprotocol(pthread_mutexattr_t* _Nonnull __attr, int __protocol) __INTRODUCED_IN(28);
 
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int pthread_mutexattr_setprotocol(pthread_mutexattr_t* _Nonnull __attr, int __protocol) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int pthread_mutex_clocklock(pthread_mutex_t* _Nonnull __mutex, clockid_t __clock,
                             const struct timespec* _Nullable __abstime) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 int pthread_mutex_destroy(pthread_mutex_t* _Nonnull __mutex);
 int pthread_mutex_init(pthread_mutex_t* _Nonnull __mutex, const pthread_mutexattr_t* _Nullable __attr);
 int pthread_mutex_lock(pthread_mutex_t* _Nonnull __mutex);
@@ -209,8 +238,12 @@
  * Note that pthread_mutex_clocklock() allows specifying an arbitrary clock and has superseded this
  * function.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_mutex_timedlock_monotonic_np(pthread_mutex_t* _Nonnull __mutex, const struct timespec* _Nullable __timeout)
     __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_mutex_trylock(pthread_mutex_t* _Nonnull __mutex);
 int pthread_mutex_unlock(pthread_mutex_t* _Nonnull __mutex);
 
@@ -220,30 +253,48 @@
 int pthread_rwlockattr_destroy(pthread_rwlockattr_t* _Nonnull __attr);
 int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t* _Nonnull __attr, int* _Nonnull __shared);
 int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* _Nonnull __attr, int __shared);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t* _Nonnull __attr, int* _Nonnull __kind)
   __INTRODUCED_IN(23);
 int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t* _Nonnull __attr, int __kind) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
 
+
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int pthread_rwlock_clockrdlock(pthread_rwlock_t* _Nonnull __rwlock, clockid_t __clock,
                                const struct timespec* _Nullable __timeout) __INTRODUCED_IN(30);
 int pthread_rwlock_clockwrlock(pthread_rwlock_t* _Nonnull __rwlock, clockid_t __clock,
                                const struct timespec* _Nullable __timeout) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 int pthread_rwlock_destroy(pthread_rwlock_t* _Nonnull __rwlock);
 int pthread_rwlock_init(pthread_rwlock_t* _Nonnull __rwlock, const pthread_rwlockattr_t* _Nullable __attr);
 int pthread_rwlock_rdlock(pthread_rwlock_t* _Nonnull __rwlock);
 int pthread_rwlock_timedrdlock(pthread_rwlock_t* _Nonnull __rwlock, const struct timespec* _Nullable __timeout);
 /* See the comment on pthread_mutex_timedlock_monotonic_np for usage of this function. */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_rwlock_timedrdlock_monotonic_np(pthread_rwlock_t* _Nonnull __rwlock,
                                             const struct timespec* _Nullable __timeout) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_rwlock_timedwrlock(pthread_rwlock_t* _Nonnull __rwlock, const struct timespec* _Nullable __timeout);
 /* See the comment on pthread_mutex_timedlock_monotonic_np for usage of this function. */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_rwlock_timedwrlock_monotonic_np(pthread_rwlock_t* _Nonnull __rwlock,
                                             const struct timespec* _Nullable __timeout) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int pthread_rwlock_tryrdlock(pthread_rwlock_t* _Nonnull __rwlock);
 int pthread_rwlock_trywrlock(pthread_rwlock_t* _Nonnull __rwlock);
 int pthread_rwlock_unlock(pthread_rwlock_t* _Nonnull __rwlock);
 int pthread_rwlock_wrlock(pthread_rwlock_t* _Nonnull __rwlock);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int pthread_barrierattr_init(pthread_barrierattr_t* _Nonnull __attr) __INTRODUCED_IN(24);
 int pthread_barrierattr_destroy(pthread_barrierattr_t* _Nonnull __attr) __INTRODUCED_IN(24);
 int pthread_barrierattr_getpshared(const pthread_barrierattr_t* _Nonnull __attr, int* _Nonnull __shared) __INTRODUCED_IN(24);
@@ -258,11 +309,17 @@
 int pthread_spin_lock(pthread_spinlock_t* _Nonnull __spinlock) __INTRODUCED_IN(24);
 int pthread_spin_trylock(pthread_spinlock_t* _Nonnull __spinlock) __INTRODUCED_IN(24);
 int pthread_spin_unlock(pthread_spinlock_t* _Nonnull __spinlock) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 pthread_t pthread_self(void) __attribute_const__;
 
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int pthread_getname_np(pthread_t __pthread, char* _Nonnull __buf, size_t __n) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 #endif
 /* TODO: this should be __USE_GNU too. */
 int pthread_setname_np(pthread_t __pthread, const char* _Nonnull __name);
@@ -301,7 +358,11 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pthread_setschedprio(pthread_t __pthread, int __priority) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int pthread_setspecific(pthread_key_t __key, const void* _Nullable __value);
 
diff --git a/libc/include/pty.h b/libc/include/pty.h
index 1cfb772..92d7fbb 100644
--- a/libc/include/pty.h
+++ b/libc/include/pty.h
@@ -49,6 +49,8 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int openpty(int* _Nonnull __pty_fd, int* _Nonnull __tty_fd, char* _Nullable __tty_name, const struct termios* _Nullable __termios_ptr, const struct winsize* _Nullable __winsize_ptr) __INTRODUCED_IN(23);
 
 /**
@@ -61,5 +63,7 @@
  * Available since API level 23.
  */
 int forkpty(int* _Nonnull __parent_pty_fd, char* _Nullable __child_tty_name, const struct termios* _Nullable __termios_ptr, const struct winsize* _Nullable __winsize_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/pwd.h b/libc/include/pwd.h
index 2b17fbf..09592bc 100644
--- a/libc/include/pwd.h
+++ b/libc/include/pwd.h
@@ -84,10 +84,14 @@
 struct passwd* _Nullable getpwuid(uid_t __uid);
 
 /* Note: Android has thousands and thousands of ids to iterate through */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 struct passwd* _Nullable getpwent(void) __INTRODUCED_IN(26);
 
 void setpwent(void) __INTRODUCED_IN(26);
 void endpwent(void) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 int getpwnam_r(const char* _Nonnull __name, struct passwd* _Nonnull __pwd, char* _Nonnull __buf, size_t __n, struct passwd* _Nullable * _Nonnull __result);
 int getpwuid_r(uid_t __uid, struct passwd* _Nonnull __pwd, char* _Nonnull __buf, size_t __n, struct passwd* _Nullable * _Nonnull __result);
diff --git a/libc/include/resolv.h b/libc/include/resolv.h
index f25484a..c49cefc 100644
--- a/libc/include/resolv.h
+++ b/libc/include/resolv.h
@@ -29,9 +29,10 @@
 #ifndef _RESOLV_H_
 #define _RESOLV_H_
 
+#include <sys/cdefs.h>
+
 #include <sys/param.h>
 #include <sys/types.h>
-#include <sys/cdefs.h>
 #include <sys/socket.h>
 #include <stdio.h>
 #include <arpa/nameser.h>
@@ -60,7 +61,11 @@
 int res_search(const char* _Nonnull __name, int __class, int __type, u_char* _Nonnull __answer, int __answer_size);
 
 #define res_randomid __res_randomid
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 u_int __res_randomid(void) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 
 __END_DECLS
 
diff --git a/libc/include/sched.h b/libc/include/sched.h
index e8f7736..7a2dcad 100644
--- a/libc/include/sched.h
+++ b/libc/include/sched.h
@@ -33,9 +33,10 @@
  * @brief Thread execution scheduling.
  */
 
+#include <sys/cdefs.h>
+
 #include <bits/timespec.h>
 #include <linux/sched.h>
-#include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
diff --git a/libc/include/search.h b/libc/include/search.h
index 85e31ee..2f43d91 100644
--- a/libc/include/search.h
+++ b/libc/include/search.h
@@ -85,6 +85,8 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int hcreate(size_t __n) __INTRODUCED_IN(28);
 
 /**
@@ -109,6 +111,8 @@
  * Available since API level 28.
  */
 ENTRY* _Nullable hsearch(ENTRY __entry, ACTION __action) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 #if defined(__USE_BSD) || defined(__USE_GNU)
 
@@ -120,6 +124,8 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int hcreate_r(size_t __n, struct hsearch_data* _Nonnull __table) __INTRODUCED_IN(28);
 
 /**
@@ -140,6 +146,8 @@
  * Available since API level 28.
  */
 int hsearch_r(ENTRY __entry, ACTION __action, ENTRY* _Nullable * _Nonnull __result, struct hsearch_data* _Nonnull __table) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 #endif
 
diff --git a/libc/include/semaphore.h b/libc/include/semaphore.h
index 6ad9ea3..9c4702d 100644
--- a/libc/include/semaphore.h
+++ b/libc/include/semaphore.h
@@ -45,7 +45,11 @@
 
 #define SEM_FAILED __BIONIC_CAST(reinterpret_cast, sem_t*, 0)
 
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int sem_clockwait(sem_t* _Nonnull __sem, clockid_t __clock, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 int sem_destroy(sem_t* _Nonnull __sem);
 int sem_getvalue(sem_t* _Nonnull __sem, int* _Nonnull __value);
 int sem_init(sem_t* _Nonnull __sem, int __shared, unsigned int __value);
@@ -59,7 +63,11 @@
  * Note that sem_clockwait() allows specifying an arbitrary clock and has superseded this
  * function.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sem_timedwait_monotonic_np(sem_t* _Nonnull __sem, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sem_trywait(sem_t* _Nonnull __sem);
 int sem_wait(sem_t* _Nonnull __sem);
 
diff --git a/libc/include/signal.h b/libc/include/signal.h
index 893fa9d..38dcbde 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -60,31 +60,73 @@
 #define si_timerid si_tid /* glibc compatibility. */
 
 int sigaction(int __signal, const struct sigaction* _Nullable __new_action, struct sigaction* _Nullable __old_action);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigaction64(int __signal, const struct sigaction64* _Nullable __new_action, struct sigaction64* _Nullable __old_action) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int siginterrupt(int __signal, int __flag);
 
 sighandler_t _Nonnull signal(int __signal, sighandler_t _Nullable __handler);
 int sigaddset(sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigaddset64(sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigdelset(sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigdelset64(sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigemptyset(sigset_t* _Nonnull __set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigemptyset64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigfillset(sigset_t* _Nonnull __set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigfillset64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigismember(const sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigismember64(const sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int sigpending(sigset_t* _Nonnull __set);
-int sigpending64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
-int sigprocmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
-int sigprocmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
-int sigsuspend(const sigset_t* _Nonnull __mask);
-int sigsuspend64(const sigset64_t* _Nonnull __mask) __INTRODUCED_IN(28);
-int sigwait(const sigset_t* _Nonnull __set, int* _Nonnull __signal);
-int sigwait64(const sigset64_t* _Nonnull __set, int* _Nonnull __signal) __INTRODUCED_IN(28);
 
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigpending64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigprocmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigprocmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigsuspend(const sigset_t* _Nonnull __mask);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigsuspend64(const sigset64_t* _Nonnull __mask) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigwait(const sigset_t* _Nonnull __set, int* _Nonnull __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigwait64(const sigset64_t* _Nonnull __set, int* _Nonnull __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int sighold(int __signal)
   __attribute__((__deprecated__("use sigprocmask() or pthread_sigmask() instead")))
   __INTRODUCED_IN(26);
@@ -97,6 +139,8 @@
   __INTRODUCED_IN(26);
 sighandler_t _Nonnull sigset(int __signal, sighandler_t _Nullable __handler)
   __attribute__((__deprecated__("use sigaction() instead"))) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 int raise(int __signal);
 int kill(pid_t __pid, int __signal);
@@ -110,17 +154,41 @@
 
 int pthread_kill(pthread_t __pthread, int __signal);
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 int pthread_sigqueue(pthread_t __pthread, int __signal, const union sigval __value) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 #endif
 
 int pthread_sigmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
-int pthread_sigmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
 
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int pthread_sigmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int sigqueue(pid_t __pid, int __signal, const union sigval __value) __INTRODUCED_IN(23);
 int sigtimedwait(const sigset_t* _Nonnull __set, siginfo_t* _Nullable __info, const struct timespec* _Nullable __timeout) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigtimedwait64(const sigset64_t* _Nonnull __set, siginfo_t* _Nullable __info, const struct timespec* _Nullable __timeout) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int sigwaitinfo(const sigset_t* _Nonnull __set, siginfo_t* _Nullable __info) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigwaitinfo64(const sigset64_t* _Nonnull __set, siginfo_t* _Nullable __info) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /**
  * Buffer size suitable for any call to sig2str().
@@ -137,6 +205,8 @@
  *
  * Available since API level 36.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(36)
 int sig2str(int __signal, char* _Nonnull __buf) __INTRODUCED_IN(36);
 
 /**
@@ -149,6 +219,8 @@
  * Available since API level 36.
  */
 int str2sig(const char* _Nonnull __name, int* _Nonnull __signal) __INTRODUCED_IN(36);
+#endif /* __BIONIC_AVAILABILITY_GUARD(36) */
+
 
 __END_DECLS
 
diff --git a/libc/include/spawn.h b/libc/include/spawn.h
index f366239..b105754 100644
--- a/libc/include/spawn.h
+++ b/libc/include/spawn.h
@@ -55,6 +55,8 @@
 typedef struct __posix_spawnattr* posix_spawnattr_t;
 typedef struct __posix_spawn_file_actions* posix_spawn_file_actions_t;
 
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int posix_spawn(pid_t* _Nullable __pid, const char* _Nonnull __path, const posix_spawn_file_actions_t _Nullable * _Nullable __actions, const posix_spawnattr_t _Nullable * _Nullable __attr, char* const _Nullable __argv[_Nullable], char* const _Nullable __env[_Nullable]) __INTRODUCED_IN(28);
 int posix_spawnp(pid_t* _Nullable __pid, const char* _Nonnull __file, const posix_spawn_file_actions_t _Nullable * _Nullable __actions, const posix_spawnattr_t _Nullable * _Nullable __attr, char* const _Nullable __argv[_Nullable], char* const _Nullable __env[_Nullable]) __INTRODUCED_IN(28);
 
@@ -89,9 +91,15 @@
 int posix_spawn_file_actions_addopen(posix_spawn_file_actions_t _Nonnull * _Nonnull __actions, int __fd, const char* _Nonnull __path, int __flags, mode_t __mode) __INTRODUCED_IN(28);
 int posix_spawn_file_actions_addclose(posix_spawn_file_actions_t _Nonnull * _Nonnull __actions, int __fd) __INTRODUCED_IN(28);
 int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t _Nonnull * _Nonnull __actions, int __fd, int __new_fd) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
 
+
+
+#if __BIONIC_AVAILABILITY_GUARD(34)
 int posix_spawn_file_actions_addchdir_np(posix_spawn_file_actions_t _Nonnull * _Nonnull __actions, const char* _Nonnull __path) __INTRODUCED_IN(34);
 int posix_spawn_file_actions_addfchdir_np(posix_spawn_file_actions_t _Nonnull * _Nonnull __actions, int __fd) __INTRODUCED_IN(34);
+#endif /* __BIONIC_AVAILABILITY_GUARD(34) */
+
 
 __END_DECLS
 
diff --git a/libc/include/stdint.h b/libc/include/stdint.h
index 322a81c..772fe8b 100644
--- a/libc/include/stdint.h
+++ b/libc/include/stdint.h
@@ -29,9 +29,10 @@
 #ifndef _STDINT_H
 #define _STDINT_H
 
+#include <sys/cdefs.h>
+
 #include <bits/wchar_limits.h>
 #include <stddef.h>
-#include <sys/cdefs.h>
 
 typedef signed char __int8_t;
 typedef unsigned char __uint8_t;
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index d24f6af..2c2dc01 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -196,7 +196,11 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int renameat2(int __old_dir_fd, const char* _Nonnull __old_path, int __new_dir_fd, const char* _Nonnull __new_path, unsigned __flags) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 
 #endif
 
@@ -205,17 +209,25 @@
 
 /* See https://android.googlesource.com/platform/bionic/+/main/docs/32-bit-abi.md */
 #if defined(__USE_FILE_OFFSET64)
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int fgetpos(FILE* _Nonnull __fp, fpos_t* _Nonnull __pos) __RENAME(fgetpos64) __INTRODUCED_IN(24);
 int fsetpos(FILE* _Nonnull __fp, const fpos_t* _Nonnull __pos) __RENAME(fsetpos64) __INTRODUCED_IN(24);
 int fseeko(FILE* _Nonnull __fp, off_t __offset, int __whence) __RENAME(fseeko64) __INTRODUCED_IN(24);
 __nodiscard off_t ftello(FILE* _Nonnull __fp) __RENAME(ftello64) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #  if defined(__USE_BSD)
 /* If __read_fn and __write_fn are both nullptr, it will cause EINVAL */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 __nodiscard FILE* _Nullable funopen(const void* _Nullable __cookie,
               int (* __BIONIC_COMPLICATED_NULLNESS __read_fn)(void* _Nonnull, char* _Nonnull, int),
               int (* __BIONIC_COMPLICATED_NULLNESS __write_fn)(void* _Nonnull, const char* _Nonnull, int),
               fpos_t (* _Nullable __seek_fn)(void* _Nonnull, fpos_t, int),
               int (* _Nullable __close_fn)(void* _Nonnull)) __RENAME(funopen64) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #  endif
 #else
 int fgetpos(FILE* _Nonnull __fp, fpos_t* _Nonnull __pos);
@@ -231,25 +243,45 @@
               int (* _Nullable __close_fn)(void* _Nonnull));
 #  endif
 #endif
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int fgetpos64(FILE* _Nonnull __fp, fpos64_t* _Nonnull __pos) __INTRODUCED_IN(24);
 int fsetpos64(FILE* _Nonnull __fp, const fpos64_t* _Nonnull __pos) __INTRODUCED_IN(24);
 int fseeko64(FILE* _Nonnull __fp, off64_t __offset, int __whence) __INTRODUCED_IN(24);
 __nodiscard off64_t ftello64(FILE* _Nonnull __fp) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #if defined(__USE_BSD)
 /* If __read_fn and __write_fn are both nullptr, it will cause EINVAL */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 __nodiscard FILE* _Nullable funopen64(const void* _Nullable __cookie,
                 int (* __BIONIC_COMPLICATED_NULLNESS __read_fn)(void* _Nonnull, char* _Nonnull, int),
                 int (* __BIONIC_COMPLICATED_NULLNESS __write_fn)(void* _Nonnull, const char* _Nonnull, int),
                 fpos64_t (* _Nullable __seek_fn)(void* _Nonnull, fpos64_t, int),
                 int (* _Nullable __close_fn)(void* _Nonnull)) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #endif
 
 __nodiscard FILE* _Nullable fopen(const char* _Nonnull __path, const char* _Nonnull __mode);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 __nodiscard FILE* _Nullable fopen64(const char* _Nonnull __path, const char* _Nonnull __mode) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 FILE* _Nullable freopen(const char* _Nullable __path, const char* _Nonnull __mode, FILE* _Nonnull __fp);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 FILE* _Nullable freopen64(const char* _Nullable __path, const char* _Nonnull __mode, FILE* _Nonnull __fp) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 __nodiscard FILE* _Nullable tmpfile(void);
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 __nodiscard FILE* _Nullable tmpfile64(void) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 int snprintf(char* __BIONIC_COMPLICATED_NULLNESS __buf, size_t __size, const char* _Nonnull __fmt, ...) __printflike(3, 4);
 int vfscanf(FILE* _Nonnull __fp, const char* _Nonnull __fmt, va_list __args) __scanflike(2, 0);
@@ -258,7 +290,11 @@
 int vsscanf(const char* _Nonnull __s, const char* _Nonnull __fmt, va_list __args) __scanflike(2, 0);
 
 #define L_ctermid 1024 /* size for ctermid() */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 char* _Nonnull ctermid(char* _Nullable __buf) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __nodiscard FILE* _Nullable fdopen(int __fd, const char* _Nonnull __mode);
 __nodiscard int fileno(FILE* _Nonnull __fp);
@@ -272,8 +308,12 @@
 int putc_unlocked(int __ch, FILE* _Nonnull __fp);
 int putchar_unlocked(int __ch);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 __nodiscard FILE* _Nullable fmemopen(void* _Nullable __buf, size_t __size, const char* _Nonnull __mode) __INTRODUCED_IN(23);
 __nodiscard FILE* _Nullable open_memstream(char* _Nonnull * _Nonnull __ptr, size_t* _Nonnull __size_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 #if defined(__USE_BSD) || defined(__BIONIC__) /* Historically bionic exposed these. */
 int  asprintf(char* _Nullable * _Nonnull __s_ptr, const char* _Nonnull __fmt, ...) __printflike(2, 3);
@@ -282,25 +322,41 @@
 void setbuffer(FILE* _Nonnull __fp, char* _Nullable __buf, int __size);
 int setlinebuf(FILE* _Nonnull __fp);
 int vasprintf(char* _Nullable * _Nonnull __s_ptr, const char* _Nonnull __fmt, va_list __args) __printflike(2, 0);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void clearerr_unlocked(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
 __nodiscard int feof_unlocked(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
 __nodiscard int ferror_unlocked(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 __nodiscard int fileno_unlocked(FILE* _Nonnull __fp) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #define fropen(cookie, fn) funopen(cookie, fn, 0, 0, 0)
 #define fwopen(cookie, fn) funopen(cookie, 0, fn, 0, 0)
 #endif
 
 #if defined(__USE_BSD)
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int fflush_unlocked(FILE* _Nullable __fp) __INTRODUCED_IN(28);
 __nodiscard int fgetc_unlocked(FILE* _Nonnull __fp) __INTRODUCED_IN(28);
 int fputc_unlocked(int __ch, FILE* _Nonnull __fp) __INTRODUCED_IN(28);
 size_t fread_unlocked(void* _Nonnull __buf, size_t __size, size_t __count, FILE* _Nonnull __fp) __INTRODUCED_IN(28);
 size_t fwrite_unlocked(const void* _Nonnull __buf, size_t __size, size_t __count, FILE* _Nonnull __fp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 #endif
 
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int fputs_unlocked(const char* _Nonnull __s, FILE* _Nonnull __fp) __INTRODUCED_IN(28);
 char* _Nullable fgets_unlocked(char* _Nonnull __buf, int __size, FILE* _Nonnull __fp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 #endif
 
 #if defined(__BIONIC_INCLUDE_FORTIFY_HEADERS)
diff --git a/libc/include/stdio_ext.h b/libc/include/stdio_ext.h
index d426a4a..9ff07da 100644
--- a/libc/include/stdio_ext.h
+++ b/libc/include/stdio_ext.h
@@ -44,6 +44,8 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 size_t __fbufsize(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
 
 /**
@@ -53,6 +55,8 @@
  * Available since API level 23.
  */
 int __freadable(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [__freading(3)](https://man7.org/linux/man-pages/man3/__freading.3.html) returns non-zero if
@@ -60,7 +64,11 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int __freading(FILE* _Nonnull __fp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /**
  * [__fwritable(3)](https://man7.org/linux/man-pages/man3/__fwritable.3.html) returns non-zero if
@@ -68,7 +76,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int __fwritable(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [__fwriting(3)](https://man7.org/linux/man-pages/man3/__fwriting.3.html) returns non-zero if
@@ -76,7 +88,11 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int __fwriting(FILE* _Nonnull __fp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /**
  * [__flbf(3)](https://man7.org/linux/man-pages/man3/__flbf.3.html) returns non-zero if
@@ -84,7 +100,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int __flbf(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [__fpurge(3)](https://man7.org/linux/man-pages/man3/__fpurge.3.html) discards the contents of
@@ -98,7 +118,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 size_t __fpending(FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * __freadahead(3) returns the number of bytes in the input buffer.
@@ -106,7 +130,11 @@
  *
  * Available since API level 34.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(34)
 size_t __freadahead(FILE* _Nonnull __fp) __INTRODUCED_IN(34);
+#endif /* __BIONIC_AVAILABILITY_GUARD(34) */
+
 
 /**
  * [_flushlbf(3)](https://man7.org/linux/man-pages/man3/_flushlbf.3.html) flushes all
@@ -114,7 +142,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void _flushlbf(void) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * `__fseterr` sets the
@@ -122,7 +154,11 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 void __fseterr(FILE* _Nonnull __fp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /** __fsetlocking() constant to query locking type. */
 #define FSETLOCKING_QUERY 0
@@ -139,6 +175,10 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int __fsetlocking(FILE* _Nonnull __fp, int __type) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 076a978..7081d7c 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -29,11 +29,12 @@
 #ifndef _STDLIB_H
 #define _STDLIB_H
 
+#include <sys/cdefs.h>
+
 #include <alloca.h>
 #include <bits/wait.h>
 #include <malloc.h>
 #include <stddef.h>
-#include <sys/cdefs.h>
 #include <xlocale.h>
 
 __BEGIN_DECLS
@@ -59,13 +60,21 @@
 char* _Nullable mkdtemp(char* _Nonnull __template);
 char* _Nullable mktemp(char* _Nonnull __template) __attribute__((__deprecated__("mktemp is unsafe, use mkstemp or tmpfile instead")));
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int mkostemp64(char* _Nonnull __template, int __flags) __INTRODUCED_IN(23);
 int mkostemp(char* _Nonnull __template, int __flags) __INTRODUCED_IN(23);
 int mkostemps64(char* _Nonnull __template, int __suffix_length, int __flags) __INTRODUCED_IN(23);
 int mkostemps(char* _Nonnull __template, int __suffix_length, int __flags) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 int mkstemp64(char* _Nonnull __template);
 int mkstemp(char* _Nonnull __template);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int mkstemps64(char* _Nonnull __template, int __flags) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 int mkstemps(char* _Nonnull __template, int __flags);
 
 int posix_memalign(void* _Nullable * _Nullable __memptr, size_t __alignment, size_t __size);
@@ -79,7 +88,11 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 __nodiscard void* _Nullable aligned_alloc(size_t __alignment, size_t __size) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __nodiscard char* _Nullable realpath(const char* _Nonnull __path, char* _Nullable __resolved);
 
@@ -122,7 +135,11 @@
  *
  * Available since API level 36.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(36)
 void qsort_r(void* _Nullable __array, size_t __n, size_t __size, int (* _Nonnull __comparator)(const void* _Nullable __lhs, const void* _Nullable __rhs, void* _Nullable __context), void* _Nullable __context) __INTRODUCED_IN(36);
+#endif /* __BIONIC_AVAILABILITY_GUARD(36) */
+
 
 uint32_t arc4random(void);
 uint32_t arc4random_uniform(uint32_t __upper_bound);
@@ -135,7 +152,11 @@
 double drand48(void);
 double erand48(unsigned short __xsubi[_Nonnull 3]);
 long jrand48(unsigned short __xsubi[_Nonnull 3]);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void lcong48(unsigned short __param[_Nonnull 7]) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 long lrand48(void);
 long mrand48(void);
 long nrand48(unsigned short __xsubi[_Nonnull 3]);
@@ -151,7 +172,11 @@
 int ptsname_r(int __fd, char* _Nonnull __buf, size_t __n);
 int unlockpt(int __fd);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int getsubopt(char* _Nonnull * _Nonnull __option, char* _Nonnull const* _Nonnull __tokens, char* _Nullable * _Nonnull __value_ptr) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 typedef struct {
   int quot;
@@ -181,13 +206,21 @@
  *
  * Returns the number of samples written to `__averages` (at most 3), and returns -1 on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 int getloadavg(double __averages[_Nonnull], int __n) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 
 /* BSD compatibility. */
 const char* _Nullable getprogname(void);
 void setprogname(const char* _Nonnull __name);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int mblen(const char* _Nullable __s, size_t __n) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 size_t mbstowcs(wchar_t* _Nullable __dst, const char* _Nullable __src, size_t __n);
 int mbtowc(wchar_t* _Nullable __wc_ptr, const char*  _Nullable __s, size_t __n);
 int wctomb(char* _Nullable __dst, wchar_t __wc);
diff --git a/libc/include/string.h b/libc/include/string.h
index 7c1c3be..79aac91 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -52,7 +52,11 @@
 int memcmp(const void* _Nonnull __lhs, const void* _Nonnull __rhs, size_t __n) __attribute_pure__;
 void* _Nonnull memcpy(void* _Nonnull, const void* _Nonnull, size_t);
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 void* _Nonnull mempcpy(void* _Nonnull __dst, const void* _Nonnull __src, size_t __n) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 #endif
 void* _Nonnull memmove(void* _Nonnull __dst, const void* _Nonnull __src, size_t __n);
 
@@ -71,7 +75,11 @@
  *
  * Returns `dst`.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(34)
 void* _Nonnull memset_explicit(void* _Nonnull __dst, int __ch, size_t __n) __INTRODUCED_IN(34);
+#endif /* __BIONIC_AVAILABILITY_GUARD(34) */
+
 
 void* _Nullable memmem(const void* _Nonnull __haystack, size_t __haystack_size, const void* _Nonnull __needle, size_t __needle_size) __attribute_pure__;
 
@@ -79,10 +87,18 @@
 char* _Nullable __strchr_chk(const char* _Nonnull __s, int __ch, size_t __n);
 #if defined(__USE_GNU)
 #if defined(__cplusplus)
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 extern "C++" char* _Nonnull strchrnul(char* _Nonnull __s, int __ch) __RENAME(strchrnul) __attribute_pure__ __INTRODUCED_IN(24);
 extern "C++" const char* _Nonnull strchrnul(const char* _Nonnull __s, int __ch) __RENAME(strchrnul) __attribute_pure__ __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #else
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 char* _Nonnull strchrnul(const char* _Nonnull __s, int __ch) __attribute_pure__ __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 #endif
 #endif
 
@@ -156,7 +172,11 @@
  * Available since API level 35.
  */
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 const char* _Nullable strerrorname_np(int __errno_value) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 #endif
 
 /**
@@ -199,10 +219,18 @@
  * It doesn't modify its argument, and in C++ it's const-correct.
  */
 #if defined(__cplusplus)
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 extern "C++" char* _Nonnull basename(char* _Nullable __path) __RENAME(__gnu_basename) __INTRODUCED_IN(23);
 extern "C++" const char* _Nonnull basename(const char* _Nonnull __path) __RENAME(__gnu_basename) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 #else
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 char* _Nonnull basename(const char* _Nonnull __path) __RENAME(__gnu_basename) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 #endif
 #endif
 
diff --git a/libc/include/strings.h b/libc/include/strings.h
index d203bd2..7543edc 100644
--- a/libc/include/strings.h
+++ b/libc/include/strings.h
@@ -43,8 +43,9 @@
  * @brief Extra string functions.
  */
 
-#include <sys/types.h>
 #include <sys/cdefs.h>
+
+#include <sys/types.h>
 #include <xlocale.h>
 
 #include <bits/strcasecmp.h>
diff --git a/libc/include/sys/cachectl.h b/libc/include/sys/cachectl.h
index b5fabe3..d06d683 100644
--- a/libc/include/sys/cachectl.h
+++ b/libc/include/sys/cachectl.h
@@ -48,7 +48,7 @@
 
 /**
  * __riscv_flush_icache(2) flushes the instruction cache for the given range of addresses.
- * The address range is currently (Linux 6.4) ignored, so both pointers may be null.
+ * The address range is currently (Linux 6.12) ignored, so both pointers may be null.
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
diff --git a/libc/include/sys/epoll.h b/libc/include/sys/epoll.h
index a5e3c14..bec7c64 100644
--- a/libc/include/sys/epoll.h
+++ b/libc/include/sys/epoll.h
@@ -88,13 +88,19 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int epoll_pwait64(int __epoll_fd, struct epoll_event* _Nonnull __events, int __event_count, int __timeout_ms, const sigset64_t* _Nullable __mask) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /**
  * Like epoll_pwait() but with a `struct timespec` timeout, for nanosecond resolution.
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 int epoll_pwait2(int __epoll_fd, struct epoll_event* _Nonnull __events, int __event_count, const struct timespec* _Nullable __timeout, const sigset_t* _Nullable __mask) __INTRODUCED_IN(35);
 
 /**
@@ -103,5 +109,7 @@
  * Available since API level 35.
  */
 int epoll_pwait2_64(int __epoll_fd, struct epoll_event* _Nonnull __events, int __event_count, const struct timespec* _Nullable __timeout, const sigset64_t* _Nullable __mask) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 1a0e7f6..38cbf2f 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -133,7 +133,11 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int mlock2(const void* _Nonnull __addr, size_t __size, int __flags) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 
 /**
  * [munlock(2)](https://man7.org/linux/man-pages/man2/munlock.2.html)
@@ -171,7 +175,11 @@
  *
  * Returns the number of bytes advised on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(31)
 ssize_t process_madvise(int __pid_fd, const struct iovec* _Nonnull __iov, size_t __count, int __advice, unsigned __flags) __INTRODUCED_IN(31);
+#endif /* __BIONIC_AVAILABILITY_GUARD(31) */
+
 
 #if defined(__USE_GNU)
 
@@ -183,7 +191,11 @@
  *
  * Returns an fd on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int memfd_create(const char* _Nonnull __name, unsigned __flags) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 
 #endif
 
@@ -220,7 +232,11 @@
  *
  * Returns 0 on success, and returns a positive error number on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int posix_madvise(void* _Nonnull __addr, size_t __size, int __advice) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [mseal(2)](https://man7.org/linux/man-pages/man2/mseal.2.html)
@@ -232,6 +248,10 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(36)
 int mseal(void* _Nonnull __addr, size_t __size, unsigned long __flags) __INTRODUCED_IN(36);
+#endif /* __BIONIC_AVAILABILITY_GUARD(36) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/msg.h b/libc/include/sys/msg.h
index 26071b1..8b619be 100644
--- a/libc/include/sys/msg.h
+++ b/libc/include/sys/msg.h
@@ -46,6 +46,8 @@
 typedef __kernel_ulong_t msglen_t;
 
 /** Not useful on Android; disallowed by SELinux. */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int msgctl(int __msg_id, int __op, struct msqid_ds* _Nullable __buf) __INTRODUCED_IN(26);
 /** Not useful on Android; disallowed by SELinux. */
 int msgget(key_t __key, int __flags) __INTRODUCED_IN(26);
@@ -53,5 +55,7 @@
 ssize_t msgrcv(int __msg_id, void* _Nonnull __msgbuf_ptr, size_t __size, long __type, int __flags) __INTRODUCED_IN(26);
 /** Not useful on Android; disallowed by SELinux. */
 int msgsnd(int __msg_id, const void* _Nonnull __msgbuf_ptr, size_t __size, int __flags) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/param.h b/libc/include/sys/param.h
index 1c991ae..99b6a07 100644
--- a/libc/include/sys/param.h
+++ b/libc/include/sys/param.h
@@ -33,10 +33,11 @@
  * @brief Various macros.
  */
 
+#include <sys/cdefs.h>
+
 #include <endian.h>
 #include <limits.h>
 #include <linux/param.h>
-#include <sys/cdefs.h>
 
 /** The unit of `st_blocks` in `struct stat`. */
 #define DEV_BSIZE 512
diff --git a/libc/include/sys/pidfd.h b/libc/include/sys/pidfd.h
index 30455bb..aaf49c9 100644
--- a/libc/include/sys/pidfd.h
+++ b/libc/include/sys/pidfd.h
@@ -49,6 +49,8 @@
  *
  * Available since API level 31.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(31)
 int pidfd_open(pid_t __pid, unsigned int __flags) __INTRODUCED_IN(31);
 
 /**
@@ -72,5 +74,7 @@
  * Available since API level 31.
  */
 int pidfd_send_signal(int __pidfd, int __sig, siginfo_t * _Nullable __info, unsigned int __flags) __INTRODUCED_IN(31);
+#endif /* __BIONIC_AVAILABILITY_GUARD(31) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/quota.h b/libc/include/sys/quota.h
index 6e32705..af09674 100644
--- a/libc/include/sys/quota.h
+++ b/libc/include/sys/quota.h
@@ -51,6 +51,10 @@
  *
  * Available since API level 26.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int quotactl(int __op, const char* _Nullable __special, int __id, char* __BIONIC_COMPLICATED_NULLNESS __addr) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/random.h b/libc/include/sys/random.h
index b4a9993..23d2c3a 100644
--- a/libc/include/sys/random.h
+++ b/libc/include/sys/random.h
@@ -52,6 +52,10 @@
  *
  * See also arc4random_buf() which is available in all API levels.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 __nodiscard ssize_t getrandom(void* _Nonnull __buffer, size_t __buffer_size, unsigned int __flags) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/resource.h b/libc/include/sys/resource.h
index 6743343..05ef2c2 100644
--- a/libc/include/sys/resource.h
+++ b/libc/include/sys/resource.h
@@ -54,7 +54,11 @@
 
 int getrusage(int __who, struct rusage* _Nonnull __usage);
 
+
+#if (!defined(__LP64__) && __ANDROID_API__ >= 24) || (defined(__LP64__))
 int prlimit(pid_t __pid, int __resource, const struct rlimit* _Nullable __new_limit, struct rlimit* _Nullable __old_limit) __INTRODUCED_IN_32(24) __INTRODUCED_IN_64(21);
+#endif /* (!defined(__LP64__) && __ANDROID_API__ >= 24) || (defined(__LP64__)) */
+
 int prlimit64(pid_t __pid, int __resource, const struct rlimit64* _Nullable __new_limit, struct rlimit64* _Nullable __old_limit);
 
 __END_DECLS
diff --git a/libc/include/sys/select.h b/libc/include/sys/select.h
index d5b3495..a7227b0 100644
--- a/libc/include/sys/select.h
+++ b/libc/include/sys/select.h
@@ -119,6 +119,10 @@
  *
  * Available since API level 28.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int pselect64(int __max_fd_plus_one, fd_set* _Nullable __read_fds, fd_set* _Nullable __write_fds, fd_set* _Nullable __exception_fds, const struct timespec* _Nullable __timeout, const sigset64_t* _Nullable __mask) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/sem.h b/libc/include/sys/sem.h
index 5682282..72f567e 100644
--- a/libc/include/sys/sem.h
+++ b/libc/include/sys/sem.h
@@ -51,12 +51,20 @@
   void* _Nullable __pad;
 };
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int semctl(int __sem_id, int __sem_num, int __op, ...) __INTRODUCED_IN(26);
 int semget(key_t __key, int __sem_count, int __flags) __INTRODUCED_IN(26);
 int semop(int __sem_id, struct sembuf* _Nonnull __ops, size_t __op_count) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int semtimedop(int __sem_id, struct sembuf* _Nonnull __ops, size_t __op_count, const struct timespec* _Nullable __timeout) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 #endif
 
 __END_DECLS
diff --git a/libc/include/sys/shm.h b/libc/include/sys/shm.h
index 8ab3d9a..a960781 100644
--- a/libc/include/sys/shm.h
+++ b/libc/include/sys/shm.h
@@ -48,6 +48,8 @@
 typedef unsigned long shmatt_t;
 
 /** Not useful on Android; disallowed by SELinux. */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 void* _Nonnull shmat(int __shm_id, const void* _Nullable __addr, int __flags) __INTRODUCED_IN(26);
 /** Not useful on Android; disallowed by SELinux. */
 int shmctl(int __shm_id, int __op, struct shmid_ds* _Nullable __buf) __INTRODUCED_IN(26);
@@ -55,5 +57,7 @@
 int shmdt(const void* _Nonnull __addr) __INTRODUCED_IN(26);
 /** Not useful on Android; disallowed by SELinux. */
 int shmget(key_t __key, size_t __size, int __flags) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 5568b7d..eaea525 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -51,6 +51,10 @@
 /**
  * Like signalfd() but allows setting a signal mask with RT signals even from a 32-bit process.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int signalfd64(int __fd, const sigset64_t* _Nonnull __mask, int __flags) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index 2633b69..0b4b248 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -33,9 +33,10 @@
  * @brief File status.
  */
 
+#include <sys/cdefs.h>
+
 #include <bits/timespec.h>
 #include <linux/stat.h>
-#include <sys/cdefs.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
@@ -176,7 +177,11 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(36)
 int lchmod(const char* _Nonnull __path, mode_t __mode) __INTRODUCED_IN(36);
+#endif /* __BIONIC_AVAILABILITY_GUARD(36) */
+
 
 /**
  * [mkdir(2)](https://man7.org/linux/man-pages/man2/mkdir.2.html)
@@ -280,7 +285,11 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int mkfifoat(int __dir_fd, const char* _Nonnull __path, mode_t __mode) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * Used in the tv_nsec field of an argument to utimensat()/futimens()
@@ -331,7 +340,11 @@
  *
  * Available since API level 30.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(30)
 int statx(int __dir_fd, const char* _Nullable __path, int __flags, unsigned __mask, struct statx* _Nonnull __buf) __INTRODUCED_IN(30);
+#endif /* __BIONIC_AVAILABILITY_GUARD(30) */
+
 #endif
 
 __END_DECLS
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index 2feca81..860824b 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -21,8 +21,9 @@
  * @brief Filesystem statistics.
  */
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/sys/syscall.h b/libc/include/sys/syscall.h
index a49323d..9341ffb 100644
--- a/libc/include/sys/syscall.h
+++ b/libc/include/sys/syscall.h
@@ -29,9 +29,10 @@
 #ifndef _SYS_SYSCALL_H_
 #define _SYS_SYSCALL_H_
 
+#include <sys/cdefs.h>
+
 #include <asm/unistd.h> /* Linux kernel __NR_* names. */
 #include <bits/glibc-syscalls.h> /* glibc-compatible SYS_* aliases. */
-#include <sys/cdefs.h>
 
 /* The syscall function itself is declared in <unistd.h>, not here. */
 
diff --git a/libc/include/sys/sysinfo.h b/libc/include/sys/sysinfo.h
index 5956feb..ed6a007 100644
--- a/libc/include/sys/sysinfo.h
+++ b/libc/include/sys/sysinfo.h
@@ -53,6 +53,8 @@
  *
  * See also sysconf().
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int get_nprocs_conf(void) __INTRODUCED_IN(23);
 
 /**
@@ -84,5 +86,7 @@
  * See also sysconf().
  */
 long get_avphys_pages(void) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/system_properties.h b/libc/include/sys/system_properties.h
index e8b6e34..1303079 100644
--- a/libc/include/sys/system_properties.h
+++ b/libc/include/sys/system_properties.h
@@ -71,9 +71,13 @@
  *
  * Available since API level 26.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 void __system_property_read_callback(const prop_info* _Nonnull __pi,
     void (* _Nonnull __callback)(void* _Nullable __cookie, const char* _Nonnull __name, const char* _Nonnull __value, uint32_t __serial),
     void* _Nullable __cookie) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /**
  * Passes a `prop_info` for each system property to the provided
@@ -101,8 +105,12 @@
  * Available since API level 26.
  */
 struct timespec;
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 bool __system_property_wait(const prop_info* _Nullable __pi, uint32_t __old_serial, uint32_t* _Nonnull __new_serial_ptr, const struct timespec* _Nullable __relative_timeout)
     __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /**
  * Deprecated: there's no limit on the length of a property name since
@@ -233,7 +241,11 @@
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 int __system_properties_zygote_reload(void) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 /**
  * Deprecated: previously for testing, but now that SystemProperties is its own
diff --git a/libc/include/sys/thread_properties.h b/libc/include/sys/thread_properties.h
index efd212a..b6214ee 100644
--- a/libc/include/sys/thread_properties.h
+++ b/libc/include/sys/thread_properties.h
@@ -50,6 +50,8 @@
  *
  * Available since API level 31.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(31)
 void __libc_get_static_tls_bounds(void* _Nonnull * _Nonnull __static_tls_begin,
                                   void* _Nonnull * _Nonnull __static_tls_end) __INTRODUCED_IN(31);
 
@@ -93,5 +95,7 @@
                           void* _Nonnull __dynamic_tls_end),
     void (* _Nonnull __on_destruction)(void* _Nonnull __dynamic_tls_begin,
                              void* _Nonnull __dynamic_tls_end)) __INTRODUCED_IN(31);
+#endif /* __BIONIC_AVAILABILITY_GUARD(31) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/time.h b/libc/include/sys/time.h
index 6ba7a37..d12c306 100644
--- a/libc/include/sys/time.h
+++ b/libc/include/sys/time.h
@@ -47,8 +47,12 @@
 int utimes(const char* _Nonnull __path, const struct timeval __times[_Nullable 2]);
 
 #if defined(__USE_BSD)
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int futimes(int __fd, const struct timeval __times[_Nullable 2]) __INTRODUCED_IN(26);
 int lutimes(const char* _Nonnull __path, const struct timeval __times[_Nullable 2]) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 #endif
 
 #if defined(__USE_GNU)
@@ -65,7 +69,11 @@
  *
  * Available since API level 26.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int futimesat(int __dir_fd, const char* __BIONIC_COMPLICATED_NULLNESS __path, const struct timeval __times[_Nullable 2]) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 #endif
 
 #define timerclear(a)   \
diff --git a/libc/include/sys/timerfd.h b/libc/include/sys/timerfd.h
index bfa9a55..f7f1ffa 100644
--- a/libc/include/sys/timerfd.h
+++ b/libc/include/sys/timerfd.h
@@ -33,10 +33,11 @@
  * @brief Timer file descriptors.
  */
 
+#include <sys/cdefs.h>
+
 #include <fcntl.h>
 #include <linux/timerfd.h>
 #include <time.h>
-#include <sys/cdefs.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/sys/timex.h b/libc/include/sys/timex.h
index 828eb47..6fb58e4 100644
--- a/libc/include/sys/timex.h
+++ b/libc/include/sys/timex.h
@@ -46,6 +46,8 @@
  *
  * Available since API level 24.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 int adjtimex(struct timex* _Nonnull __buf) __INTRODUCED_IN(24);
 
 /**
@@ -56,5 +58,7 @@
  * Available since API level 24.
  */
 int clock_adjtime(clockid_t __clock, struct timex* _Nonnull __tx) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 __END_DECLS
diff --git a/libc/include/sys/types.h b/libc/include/sys/types.h
index 4622a4e..0446260 100644
--- a/libc/include/sys/types.h
+++ b/libc/include/sys/types.h
@@ -29,9 +29,10 @@
 #ifndef _SYS_TYPES_H_
 #define _SYS_TYPES_H_
 
+#include <sys/cdefs.h>
+
 #include <stddef.h>
 #include <stdint.h>
-#include <sys/cdefs.h>
 
 #include <linux/types.h>
 #include <linux/posix_types.h>
diff --git a/libc/include/sys/uio.h b/libc/include/sys/uio.h
index d3e6561..eff3b14 100644
--- a/libc/include/sys/uio.h
+++ b/libc/include/sys/uio.h
@@ -69,6 +69,8 @@
  *
  * Available since API level 24.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(24)
 ssize_t preadv(int __fd, const struct iovec* _Nonnull __iov, int __count, off_t __offset) __RENAME_IF_FILE_OFFSET64(preadv64) __INTRODUCED_IN(24);
 
 /**
@@ -96,6 +98,8 @@
  * Available since API level 24.
  */
 ssize_t pwritev64(int __fd, const struct iovec* _Nonnull __iov, int __count, off64_t __offset) __INTRODUCED_IN(24);
+#endif /* __BIONIC_AVAILABILITY_GUARD(24) */
+
 
 /**
  * [preadv2(2)](https://man7.org/linux/man-pages/man2/preadv2.2.html) reads
@@ -107,6 +111,8 @@
  *
  * Available since API level 33.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(33)
 ssize_t preadv2(int __fd, const struct iovec* _Nonnull __iov, int __count, off_t __offset, int __flags) __RENAME_IF_FILE_OFFSET64(preadv64v2) __INTRODUCED_IN(33);
 
 /**
@@ -134,6 +140,8 @@
  * Available since API level 33.
  */
 ssize_t pwritev64v2(int __fd, const struct iovec* _Nonnull __iov, int __count, off64_t __offset, int __flags) __INTRODUCED_IN(33);
+#endif /* __BIONIC_AVAILABILITY_GUARD(33) */
+
 
 /**
  * [process_vm_readv(2)](https://man7.org/linux/man-pages/man2/process_vm_readv.2.html)
@@ -144,6 +152,8 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 ssize_t process_vm_readv(pid_t __pid, const struct iovec* __BIONIC_COMPLICATED_NULLNESS __local_iov, unsigned long __local_iov_count, const struct iovec* __BIONIC_COMPLICATED_NULLNESS __remote_iov, unsigned long __remote_iov_count, unsigned long __flags) __INTRODUCED_IN(23);
 
 /**
@@ -156,6 +166,8 @@
  * Available since API level 23.
  */
 ssize_t process_vm_writev(pid_t __pid, const struct iovec* __BIONIC_COMPLICATED_NULLNESS __local_iov, unsigned long __local_iov_count, const struct iovec* __BIONIC_COMPLICATED_NULLNESS __remote_iov, unsigned long __remote_iov_count, unsigned long __flags) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 #endif
 
diff --git a/libc/include/sys/un.h b/libc/include/sys/un.h
index 83c1d17..c2bfcb0 100644
--- a/libc/include/sys/un.h
+++ b/libc/include/sys/un.h
@@ -33,9 +33,10 @@
  * @brief Unix domain sockets.
  */
 
+#include <sys/cdefs.h>
+
 #include <bits/sa_family_t.h>
 #include <linux/un.h>
-#include <sys/cdefs.h>
 
 #if defined(__USE_BSD) || defined(__USE_GNU)
 #include <string.h>
diff --git a/libc/include/sys/vfs.h b/libc/include/sys/vfs.h
index 1a640ba..5d078be 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -29,8 +29,9 @@
 #ifndef _SYS_VFS_H_
 #define _SYS_VFS_H_
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index 5208366..632aa43 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <bits/wait.h>
 #include <sys/cdefs.h>
+
+#include <bits/wait.h>
 #include <sys/types.h>
 #include <sys/resource.h>
 #include <linux/wait.h>
diff --git a/libc/include/sys/xattr.h b/libc/include/sys/xattr.h
index 38c11e2..ebe4eb8 100644
--- a/libc/include/sys/xattr.h
+++ b/libc/include/sys/xattr.h
@@ -33,8 +33,9 @@
  * @brief Extended attribute functions.
  */
 
-#include <linux/xattr.h>
 #include <sys/cdefs.h>
+
+#include <linux/xattr.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/syslog.h b/libc/include/syslog.h
index 33979f0..7a594f1 100644
--- a/libc/include/syslog.h
+++ b/libc/include/syslog.h
@@ -56,8 +56,9 @@
 
 #pragma once
 
-#include <stdio.h>
 #include <sys/cdefs.h>
+
+#include <stdio.h>
 #include <stdarg.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/time.h b/libc/include/time.h
index e9d6569..6c9b761 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -166,7 +166,11 @@
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 time_t mktime_z(timezone_t _Nonnull __tz, struct tm* _Nonnull __tm) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 /**
  * [localtime(3)](https://man7.org/linux/man-pages/man3/localtime.3p.html) converts
@@ -200,7 +204,11 @@
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 struct tm* _Nullable localtime_rz(timezone_t _Nonnull __tz, const time_t* _Nonnull __t, struct tm* _Nonnull __tm) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 /**
  * Inverse of localtime().
@@ -314,6 +322,8 @@
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 timezone_t _Nullable tzalloc(const char* _Nullable __id) __INTRODUCED_IN(35);
 
 /**
@@ -326,6 +336,8 @@
  * Available since API level 35.
  */
 void tzfree(timezone_t _Nullable __tz) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 /**
  * [clock(3)](https://man7.org/linux/man-pages/man3/clock.3.html)
@@ -345,7 +357,11 @@
  *
  * Returns 0 on success, and returns -1 and returns an error number on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int clock_getcpuclockid(pid_t __pid, clockid_t* _Nonnull __clock) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * [clock_getres(2)](https://man7.org/linux/man-pages/man2/clock_getres.2.html)
@@ -459,7 +475,11 @@
  * Available since API level 29 for TIME_UTC; other bases arrived later.
  * Code for Android should prefer clock_gettime().
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 int timespec_get(struct timespec* _Nonnull __ts, int __base) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 
 /**
  * timespec_getres(3) is equivalent to clock_getres() for the clock corresponding to the given base.
@@ -469,6 +489,10 @@
  * Available since API level 35.
  * Code for Android should prefer clock_gettime().
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 int timespec_getres(struct timespec* _Nonnull __ts, int __base) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 __END_DECLS
diff --git a/libc/include/uchar.h b/libc/include/uchar.h
index 55a36e7..94efb2d 100644
--- a/libc/include/uchar.h
+++ b/libc/include/uchar.h
@@ -33,9 +33,10 @@
  * @brief Unicode functions.
  */
 
-#include <stddef.h>
 #include <sys/cdefs.h>
 
+#include <stddef.h>
+
 #include <bits/bionic_multibyte_result.h>
 #include <bits/mbstate_t.h>
 
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 9bc01f0..e623339 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <stddef.h>
 #include <sys/cdefs.h>
+
+#include <stddef.h>
 #include <sys/types.h>
 #include <sys/select.h>
 
@@ -100,7 +101,11 @@
  *
  * Available since API level 35.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(35)
 pid_t _Fork(void) __INTRODUCED_IN(35);
+#endif /* __BIONIC_AVAILABILITY_GUARD(35) */
+
 
 /**
  * [vfork(2)](https://man7.org/linux/man-pages/man2/vfork.2.html) creates a new
@@ -145,7 +150,11 @@
 int execlp(const char* _Nonnull __file, const char* _Nullable __arg0, ...) __attribute__((__sentinel__));
 int execle(const char* _Nonnull __path, const char* _Nullable __arg0, ... /*,  char* const* __envp */)
     __attribute__((__sentinel__(1)));
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int fexecve(int __fd, char* _Nullable const* _Nullable __argv, char* _Nullable const* _Nullable __envp) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int nice(int __incr);
 
@@ -246,7 +255,11 @@
 int getresuid(uid_t* _Nonnull __ruid, uid_t* _Nonnull __euid, uid_t* _Nonnull __suid);
 int getresgid(gid_t* _Nonnull __rgid, gid_t* _Nonnull __egid, gid_t* _Nonnull __sgid);
 char* _Nullable getlogin(void);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int getlogin_r(char* _Nonnull __buffer, size_t __buffer_size) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 long fpathconf(int __fd, int __name);
 long pathconf(const char* _Nonnull __path, int __name);
@@ -298,7 +311,11 @@
 
 void sync(void);
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int syncfs(int __fd) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 #endif
 
 int close(int __fd);
@@ -360,7 +377,11 @@
 int usleep(useconds_t __microseconds);
 
 int gethostname(char* _Nonnull _buf, size_t __buf_size);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int sethostname(const char* _Nonnull __name, size_t __n) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 int brk(void* _Nonnull __addr);
 void* _Nullable sbrk(ptrdiff_t __increment);
@@ -403,8 +424,12 @@
     } while (_rc == -1 && errno == EINTR); \
     _rc; })
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int getdomainname(char* _Nonnull __buf, size_t __buf_size) __INTRODUCED_IN(26);
 int setdomainname(const char* _Nonnull __name, size_t __n) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /**
  * [copy_file_range(2)](https://man7.org/linux/man-pages/man2/copy_file_range.2.html) copies
@@ -415,7 +440,11 @@
  * Returns the number of bytes copied on success, and returns -1 and sets
  * `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(34)
 ssize_t copy_file_range(int __fd_in, off64_t* _Nullable __off_in, int __fd_out, off64_t* _Nullable __off_out, size_t __length, unsigned int __flags) __INTRODUCED_IN(34);
+#endif /* __BIONIC_AVAILABILITY_GUARD(34) */
+
 
 #if __ANDROID_API__ >= 28
 void swab(const void* _Nonnull __src, void* _Nonnull __dst, ssize_t __byte_count) __INTRODUCED_IN(28);
@@ -435,7 +464,11 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(34)
 int close_range(unsigned int __min_fd, unsigned int __max_fd, int __flags) __INTRODUCED_IN(34);
+#endif /* __BIONIC_AVAILABILITY_GUARD(34) */
+
 
 #if defined(__BIONIC_INCLUDE_FORTIFY_HEADERS)
 #define _UNISTD_H_
diff --git a/libc/include/utmp.h b/libc/include/utmp.h
index d249f8a..1674491 100644
--- a/libc/include/utmp.h
+++ b/libc/include/utmp.h
@@ -131,6 +131,10 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int login_tty(int __fd) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 __END_DECLS
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index e86f94d..56594dc 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -75,7 +75,11 @@
 wchar_t* _Nonnull wcpncpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 size_t wcrtomb(char* _Nullable __buf, wchar_t __wc, mbstate_t* _Nullable __ps);
 int wcscasecmp(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int wcscasecmp_l(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs, locale_t _Nonnull __l) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 wchar_t* _Nonnull wcscat(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src);
 wchar_t* _Nullable wcschr(const wchar_t * _Nonnull __s, wchar_t __wc);
 int wcscmp(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs);
@@ -83,10 +87,18 @@
 wchar_t* _Nonnull wcscpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src);
 size_t wcscspn(const wchar_t* _Nonnull __s, const wchar_t* _Nonnull __accept);
 size_t wcsftime(wchar_t* _Nonnull __buf, size_t __n, const wchar_t* _Nullable __fmt, const struct tm* _Nonnull __tm);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 size_t wcsftime_l(wchar_t* _Nonnull __buf, size_t __n, const wchar_t* _Nullable __fmt, const struct tm* _Nonnull __tm, locale_t _Nonnull __l) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 size_t wcslen(const wchar_t* _Nonnull __s);
 int wcsncasecmp(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs, size_t __n);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int wcsncasecmp_l(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs, size_t __n, locale_t _Nonnull __l) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 wchar_t* _Nonnull wcsncat(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 int wcsncmp(const wchar_t* _Nonnull __lhs, const wchar_t* _Nonnull __rhs, size_t __n);
 wchar_t* _Nonnull wcsncpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
@@ -117,7 +129,11 @@
 int wmemcmp(const wchar_t* _Nullable __lhs, const wchar_t* _Nullable __rhs, size_t __n);
 wchar_t* _Nonnull wmemcpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 wchar_t* _Nonnull wmempcpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 #endif
 wchar_t* _Nonnull wmemmove(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 wchar_t* _Nonnull wmemset(wchar_t* _Nonnull __dst, wchar_t __wc, size_t __n);
@@ -133,7 +149,11 @@
 size_t wcslcat(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 size_t wcslcpy(wchar_t* _Nonnull __dst, const wchar_t* _Nonnull __src, size_t __n);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 FILE* _Nullable open_wmemstream(wchar_t* _Nonnull * _Nonnull __ptr, size_t* _Nonnull  __size_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 wchar_t* _Nullable wcsdup(const wchar_t* _Nonnull __s);
 size_t wcsnlen(const wchar_t* _Nonnull __s, size_t __n);
 
diff --git a/libc/include/wctype.h b/libc/include/wctype.h
index 4f6f81f..30ec04f 100644
--- a/libc/include/wctype.h
+++ b/libc/include/wctype.h
@@ -29,8 +29,9 @@
 #ifndef _WCTYPE_H_
 #define _WCTYPE_H_
 
-#include <bits/wctype.h>
 #include <sys/cdefs.h>
+
+#include <bits/wctype.h>
 #include <xlocale.h>
 
 __BEGIN_DECLS
@@ -51,8 +52,12 @@
 wint_t towlower_l(wint_t __wc, locale_t _Nonnull __l);
 wint_t towupper_l(wint_t __wc, locale_t _Nonnull __l);
 
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 wint_t towctrans_l(wint_t __wc, wctrans_t _Nonnull __transform, locale_t _Nonnull __l) __INTRODUCED_IN(26);
 wctrans_t _Nonnull wctrans_l(const char* _Nonnull __name, locale_t _Nonnull __l) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 wctype_t wctype_l(const char* _Nonnull __name, locale_t _Nonnull __l);
 int iswctype_l(wint_t __wc, wctype_t __transform, locale_t _Nonnull __l);
diff --git a/libc/kernel/tools/defaults.py b/libc/kernel/tools/defaults.py
index 06afb25..a71318e 100644
--- a/libc/kernel/tools/defaults.py
+++ b/libc/kernel/tools/defaults.py
@@ -133,6 +133,9 @@
           # These are required to support the above functions.
           "__fswahw32",
           "__fswahb32",
+          # As are these, for ILP32.
+          "__arch_swab32",
+          "__arch_swab64",
           # This is used by various macros in <linux/ioprio.h>.
           "ioprio_value",
 
diff --git a/libc/kernel/uapi/asm-arm/asm/swab.h b/libc/kernel/uapi/asm-arm/asm/swab.h
index 7684c22..3fff953 100644
--- a/libc/kernel/uapi/asm-arm/asm/swab.h
+++ b/libc/kernel/uapi/asm-arm/asm/swab.h
@@ -11,7 +11,18 @@
 #ifndef __STRICT_ANSI__
 #define __SWAB_64_THRU_32__
 #endif
+static inline __attribute__((__const__)) __u32 __arch_swab32(__u32 x) {
+  __u32 t;
 #ifndef __thumb__
+  if(! __builtin_constant_p(x)) {
+    asm("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
+  } else
 #endif
+  t = x ^ ((x << 16) | (x >> 16));
+  x = (x << 24) | (x >> 8);
+  t &= ~0x00FF0000;
+  x ^= (t >> 8);
+  return x;
+}
 #define __arch_swab32 __arch_swab32
 #endif
diff --git a/libc/kernel/uapi/asm-x86/asm/swab.h b/libc/kernel/uapi/asm-x86/asm/swab.h
index 31c850d..ce43658 100644
--- a/libc/kernel/uapi/asm-x86/asm/swab.h
+++ b/libc/kernel/uapi/asm-x86/asm/swab.h
@@ -8,9 +8,27 @@
 #define _ASM_X86_SWAB_H
 #include <linux/types.h>
 #include <linux/compiler.h>
+static inline __attribute__((__const__)) __u32 __arch_swab32(__u32 val) {
+  asm("bswapl %0" : "=r" (val) : "0" (val));
+  return val;
+}
 #define __arch_swab32 __arch_swab32
+static inline __attribute__((__const__)) __u64 __arch_swab64(__u64 val) {
 #ifdef __i386__
+  union {
+    struct {
+      __u32 a;
+      __u32 b;
+    } s;
+    __u64 u;
+  } v;
+  v.u = val;
+  asm("bswapl %0; bswapl %1; xchgl %0,%1" : "=r" (v.s.a), "=r" (v.s.b) : "0" (v.s.a), "1" (v.s.b));
+  return v.u;
 #else
+  asm("bswapq %0" : "=r" (val) : "0" (val));
+  return val;
 #endif
+}
 #define __arch_swab64 __arch_swab64
 #endif
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 0d2e42f..d8636a2 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -591,7 +591,6 @@
     killpg;
     klogctl;
     labs;
-    lchmod; # introduced=36
     lchown;
     lcong48; # introduced=23
     ldexp;
@@ -671,7 +670,6 @@
     mprotect;
     mrand48;
     mremap;
-    mseal; # introduced=36
     msync;
     munlock;
     munlockall;
@@ -846,7 +844,6 @@
     pwrite;
     pwrite64;
     qsort;
-    qsort_r; # introduced=36
     quick_exit;
     raise;
     rand;
@@ -955,7 +952,6 @@
     setvbuf;
     setxattr;
     shutdown;
-    sig2str; # introduced=36
     sigaction;
     sigaddset;
     sigaltstack;
@@ -998,7 +994,6 @@
     stdout; # var introduced=23
     stpcpy;
     stpncpy;
-    str2sig; # introduced=36
     strcasecmp;
     strcasecmp_l; # introduced=23
     strcasestr;
@@ -1613,6 +1608,15 @@
     __system_properties_zygote_reload; # apex
 } LIBC_U;
 
+LIBC_36 { # introduced=36
+  global:
+    lchmod;
+    mseal;
+    qsort_r;
+    sig2str;
+    str2sig;
+} LIBC_V;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86
diff --git a/libc/private/bionic_constants.h b/libc/private/bionic_constants.h
index 6274fe2..ce484d8 100644
--- a/libc/private/bionic_constants.h
+++ b/libc/private/bionic_constants.h
@@ -16,6 +16,7 @@
 
 #pragma once
 
+#define US_PER_S 1'000'000LL
 #define NS_PER_S 1'000'000'000LL
 
 // Size of the shadow call stack. This can be small because these stacks only
diff --git a/libc/private/bionic_globals.h b/libc/private/bionic_globals.h
index 02713fc..cd6dca9 100644
--- a/libc/private/bionic_globals.h
+++ b/libc/private/bionic_globals.h
@@ -158,6 +158,9 @@
 
 __LIBC_HIDDEN__ libc_shared_globals* __libc_shared_globals();
 __LIBC_HIDDEN__ bool __libc_mte_enabled();
+__LIBC_HIDDEN__ void __libc_init_mte(const memtag_dynamic_entries_t*, const void*, size_t,
+                                     uintptr_t);
+__LIBC_HIDDEN__ void __libc_init_mte_stack(void*);
 __LIBC_HIDDEN__ void __libc_init_fdsan();
 __LIBC_HIDDEN__ void __libc_init_fdtrack();
 __LIBC_HIDDEN__ void __libc_init_profiling_handlers();
diff --git a/libc/private/bionic_time_conversions.h b/libc/private/bionic_time_conversions.h
index c6b3c78..ce7de0d 100644
--- a/libc/private/bionic_time_conversions.h
+++ b/libc/private/bionic_time_conversions.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _BIONIC_TIME_CONVERSIONS_H
-#define _BIONIC_TIME_CONVERSIONS_H
+#pragma once
 
 #include <errno.h>
 #include <time.h>
@@ -35,20 +34,21 @@
 
 #include "private/bionic_constants.h"
 
-__BEGIN_DECLS
+bool timespec_from_timeval(timespec& ts, const timeval& tv);
+void timespec_from_ms(timespec& ts, const int ms);
 
-__LIBC_HIDDEN__ bool timespec_from_timeval(timespec& ts, const timeval& tv);
-__LIBC_HIDDEN__ void timespec_from_ms(timespec& ts, const int ms);
+void timeval_from_timespec(timeval& tv, const timespec& ts);
 
-__LIBC_HIDDEN__ void timeval_from_timespec(timeval& tv, const timespec& ts);
+void monotonic_time_from_realtime_time(timespec& monotonic_time, const timespec& realtime_time);
+void realtime_time_from_monotonic_time(timespec& realtime_time, const timespec& monotonic_time);
 
-__LIBC_HIDDEN__ void monotonic_time_from_realtime_time(timespec& monotonic_time,
-                                                       const timespec& realtime_time);
+static inline int64_t to_ns(const timespec& ts) {
+  return ts.tv_sec * NS_PER_S + ts.tv_nsec;
+}
 
-__LIBC_HIDDEN__ void realtime_time_from_monotonic_time(timespec& realtime_time,
-                                                       const timespec& monotonic_time);
-
-__END_DECLS
+static inline int64_t to_us(const timeval& tv) {
+  return tv.tv_sec * US_PER_S + tv.tv_usec;
+}
 
 static inline int check_timespec(const timespec* ts, bool null_allowed) {
   if (null_allowed && ts == nullptr) {
@@ -76,5 +76,3 @@
   }
 }
 #endif
-
-#endif
diff --git a/libc/private/bsd_sys_param.h b/libc/private/bsd_sys_param.h
deleted file mode 100644
index ab54aa0..0000000
--- a/libc/private/bsd_sys_param.h
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * Copyright (C) 2014 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#pragma once
-
-#include <inttypes.h>
-
-/* OpenBSD has these in <sys/param.h>, but "ALIGN" isn't something we want to reserve. */
-#define ALIGNBYTES (sizeof(uintptr_t) - 1)
-#define ALIGN(p) ((__BIONIC_CAST(reinterpret_cast, uintptr_t, p) + ALIGNBYTES) & ~ALIGNBYTES)
diff --git a/libc/stdio/stdio.cpp b/libc/stdio/stdio.cpp
index 37b9665..a5f2f81 100644
--- a/libc/stdio/stdio.cpp
+++ b/libc/stdio/stdio.cpp
@@ -58,8 +58,6 @@
 #include "private/bionic_fortify.h"
 #include "private/thread_private.h"
 
-#include "private/bsd_sys_param.h" // For ALIGN/ALIGNBYTES.
-
 #define	NDYNAMIC 10		/* add ten more whenever necessary */
 
 #define PRINTF_IMPL(expr) \
@@ -135,12 +133,14 @@
 };
 
 static glue* moreglue(int n) {
-  char* data = new char[sizeof(glue) + ALIGNBYTES + n * sizeof(FILE) + n * sizeof(__sfileext)];
+  char* data = new char[sizeof(glue) +
+                        alignof(FILE) + n * sizeof(FILE) +
+                        alignof(__sfileext) + n * sizeof(__sfileext)];
   if (data == nullptr) return nullptr;
 
   glue* g = reinterpret_cast<glue*>(data);
-  FILE* p = reinterpret_cast<FILE*>(ALIGN(data + sizeof(*g)));
-  __sfileext* pext = reinterpret_cast<__sfileext*>(ALIGN(data + sizeof(*g)) + n * sizeof(FILE));
+  FILE* p = reinterpret_cast<FILE*>(__builtin_align_up(g + 1, alignof(FILE)));
+  __sfileext* pext = reinterpret_cast<__sfileext*>(__builtin_align_up(p + n, alignof(__sfileext)));
   g->next = nullptr;
   g->niobs = n;
   g->iobs = p;
diff --git a/libc/upstream-openbsd/android/include/openbsd-compat.h b/libc/upstream-openbsd/android/include/openbsd-compat.h
index cbc52b5..ac6840a 100644
--- a/libc/upstream-openbsd/android/include/openbsd-compat.h
+++ b/libc/upstream-openbsd/android/include/openbsd-compat.h
@@ -25,8 +25,6 @@
 
 #include <sys/random.h> // For getentropy.
 
-#include "private/bsd_sys_param.h"
-
 #define __BEGIN_HIDDEN_DECLS _Pragma("GCC visibility push(hidden)")
 #define __END_HIDDEN_DECLS _Pragma("GCC visibility pop")
 
diff --git a/linker/linker_phdr_16kib_compat.cpp b/linker/linker_phdr_16kib_compat.cpp
index e084635..a4d8459 100644
--- a/linker/linker_phdr_16kib_compat.cpp
+++ b/linker/linker_phdr_16kib_compat.cpp
@@ -223,8 +223,6 @@
   // the zip offset must be added to find the segment offset.
   const ElfW(Addr) offset = file_offset_ + align_down(phdr->p_offset, kCompatPageSize);
 
-  int prot = PFLAGS_TO_PROT(phdr->p_flags);
-
   CHECK(should_use_16kib_app_compat_);
 
   // Since the 4KiB max-page-size ELF is not properly aligned, loading it by
diff --git a/tests/Android.bp b/tests/Android.bp
index ae8420a..7137a2c 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -1223,6 +1223,7 @@
 
     shared_libs: [
         "libbase",
+        "liblog",
     ],
 
     target: {
diff --git a/tests/complex_test.cpp b/tests/complex_test.cpp
index 8fdb2b2..ed0109a 100644
--- a/tests/complex_test.cpp
+++ b/tests/complex_test.cpp
@@ -20,6 +20,9 @@
 #if !defined(__INTRODUCED_IN)
 #define __INTRODUCED_IN(x)
 #endif
+#if !defined(__BIONIC_AVAILABILITY_GUARD)
+#define __BIONIC_AVAILABILITY_GUARD(x) 1
+#endif
 
 // libc++ actively gets in the way of including <complex.h> from C++, so we
 // have to be naughty.
diff --git a/tests/headers/posix/stdatomic_h.c b/tests/headers/posix/stdatomic_h.c
new file mode 100644
index 0000000..05be859
--- /dev/null
+++ b/tests/headers/posix/stdatomic_h.c
@@ -0,0 +1,175 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdatomic.h>
+
+#include "header_checks.h"
+
+static void stdatomic_h() {
+  TYPE(atomic_flag);
+  TYPE(atomic_bool);
+  TYPE(atomic_char);
+  TYPE(atomic_schar);
+  TYPE(atomic_uchar);
+  TYPE(atomic_short);
+  TYPE(atomic_ushort);
+  TYPE(atomic_int);
+  TYPE(atomic_uint);
+  TYPE(atomic_long);
+  TYPE(atomic_ulong);
+  TYPE(atomic_llong);
+  TYPE(atomic_ullong);
+#if !defined(__GLIBC__)
+  TYPE(atomic_char16_t);
+  TYPE(atomic_char32_t);
+#endif
+  TYPE(atomic_wchar_t);
+  TYPE(atomic_int_least8_t);
+  TYPE(atomic_uint_least8_t);
+  TYPE(atomic_int_least16_t);
+  TYPE(atomic_uint_least16_t);
+  TYPE(atomic_int_least32_t);
+  TYPE(atomic_uint_least32_t);
+  TYPE(atomic_int_least64_t);
+  TYPE(atomic_uint_least64_t);
+  TYPE(atomic_int_fast8_t);
+  TYPE(atomic_uint_fast8_t);
+  TYPE(atomic_int_fast16_t);
+  TYPE(atomic_uint_fast16_t);
+  TYPE(atomic_int_fast32_t);
+  TYPE(atomic_uint_fast32_t);
+  TYPE(atomic_int_fast64_t);
+  TYPE(atomic_uint_fast64_t);
+  TYPE(atomic_intptr_t);
+  TYPE(atomic_uintptr_t);
+  TYPE(atomic_size_t);
+  TYPE(atomic_ptrdiff_t);
+  TYPE(atomic_intmax_t);
+  TYPE(atomic_uintmax_t);
+
+  memory_order m1 = memory_order_relaxed;
+  memory_order m2 = memory_order_consume;
+  memory_order m3 = memory_order_acquire;
+  memory_order m4 = memory_order_release;
+  memory_order m5 = memory_order_acq_rel;
+  memory_order m6 = memory_order_seq_cst;
+
+  MACRO(ATOMIC_BOOL_LOCK_FREE);
+  MACRO(ATOMIC_CHAR_LOCK_FREE);
+  MACRO(ATOMIC_CHAR16_T_LOCK_FREE);
+  MACRO(ATOMIC_CHAR32_T_LOCK_FREE);
+  MACRO(ATOMIC_WCHAR_T_LOCK_FREE);
+  MACRO(ATOMIC_SHORT_LOCK_FREE);
+  MACRO(ATOMIC_INT_LOCK_FREE);
+  MACRO(ATOMIC_LONG_LOCK_FREE);
+  MACRO(ATOMIC_LLONG_LOCK_FREE);
+  MACRO(ATOMIC_POINTER_LOCK_FREE);
+
+  atomic_flag f = ATOMIC_FLAG_INIT;
+  atomic_int i = ATOMIC_VAR_INIT(123);
+
+  // TODO: remove this #if after the next toolchain update (http://b/374104004).
+#if !defined(__GLIBC__)
+  i = kill_dependency(i);
+#endif
+
+#if !defined(atomic_compare_exchange_strong)
+#error atomic_compare_exchange_strong
+#endif
+#if !defined(atomic_compare_exchange_strong_explicit)
+#error atomic_compare_exchange_strong_explicit
+#endif
+#if !defined(atomic_compare_exchange_weak)
+#error atomic_compare_exchange_weak
+#endif
+#if !defined(atomic_compare_exchange_weak_explicit)
+#error atomic_compare_exchange_weak_explicit
+#endif
+#if !defined(atomic_exchange)
+#error atomic_exchange
+#endif
+#if !defined(atomic_exchange_explicit)
+#error atomic_exchange_explicit
+#endif
+#if !defined(atomic_fetch_add)
+#error atomic_fetch_add
+#endif
+#if !defined(atomic_fetch_add_explicit)
+#error atomic_fetch_add_explicit
+#endif
+#if !defined(atomic_fetch_and)
+#error atomic_fetch_and
+#endif
+#if !defined(atomic_fetch_and_explicit)
+#error atomic_fetch_and_explicit
+#endif
+#if !defined(atomic_fetch_or)
+#error atomic_fetch_or
+#endif
+#if !defined(atomic_fetch_or_explicit)
+#error atomic_fetch_or_explicit
+#endif
+#if !defined(atomic_fetch_sub)
+#error atomic_fetch_sub
+#endif
+#if !defined(atomic_fetch_sub_explicit)
+#error atomic_fetch_sub_explicit
+#endif
+#if !defined(atomic_fetch_xor)
+#error atomic_fetch_xor
+#endif
+#if !defined(atomic_fetch_xor_explicit)
+#error atomic_fetch_xor_explicit
+#endif
+#if !defined(atomic_init)
+#error atomic_init
+#endif
+#if !defined(atomic_is_lock_free)
+#error atomic_is_lock_free
+#endif
+#if !defined(atomic_load)
+#error atomic_load
+#endif
+#if !defined(atomic_load_explicit)
+#error atomic_load_explicit
+#endif
+#if !defined(atomic_store)
+#error atomic_store
+#endif
+#if !defined(atomic_store_explicit)
+#error atomic_store_explicit
+#endif
+
+  FUNCTION(atomic_flag_clear, void (*f)(volatile atomic_flag*));
+  FUNCTION(atomic_flag_clear_explicit, void (*f)(volatile atomic_flag*, memory_order));
+  FUNCTION(atomic_flag_test_and_set, bool (*f)(volatile atomic_flag*));
+  FUNCTION(atomic_flag_test_and_set_explicit, bool (*f)(volatile atomic_flag*, memory_order));
+
+  FUNCTION(atomic_signal_fence, void (*f)(memory_order));
+  FUNCTION(atomic_thread_fence, void (*f)(memory_order));
+}
diff --git a/tests/malloc_stress_test.cpp b/tests/malloc_stress_test.cpp
index b5b06ab..00f5919 100644
--- a/tests/malloc_stress_test.cpp
+++ b/tests/malloc_stress_test.cpp
@@ -27,10 +27,58 @@
 #include <thread>
 #include <vector>
 
-#include <android-base/strings.h>
 #if defined(__BIONIC__)
 #include <meminfo/procmeminfo.h>
 #include <procinfo/process_map.h>
+
+#include <log/log.h>
+#include <log/log_read.h>
+#endif
+
+#if defined(__BIONIC__)
+static void PrintLogStats(uint64_t& last_time) {
+  logger_list* logger =
+      android_logger_list_open(android_name_to_log_id("main"), ANDROID_LOG_NONBLOCK, 0, getpid());
+  if (logger == nullptr) {
+    printf("Failed to open log for main\n");
+    return;
+  }
+
+  uint64_t last_message_time = last_time;
+  while (true) {
+    log_msg entry;
+    ssize_t retval = android_logger_list_read(logger, &entry);
+    if (retval == 0) {
+      break;
+    }
+    if (retval < 0) {
+      if (retval == -EINTR) {
+        continue;
+      }
+      // EAGAIN means there is nothing left to read when ANDROID_LOG_NONBLOCK is set.
+      if (retval != -EAGAIN) {
+        printf("Failed to read log entry: %s\n", strerrordesc_np(retval));
+      }
+      break;
+    }
+    if (entry.msg() == nullptr) {
+      continue;
+    }
+    // Only print allocator tagged log entries.
+    std::string_view tag(entry.msg() + 1);
+    if (tag != "scudo" && tag != "jemalloc") {
+      continue;
+    }
+    if (entry.nsec() > last_time) {
+      printf("  %s\n", &tag.back() + 2);
+      // Only update the last time outside this loop just in case two or more
+      // messages have the same timestamp.
+      last_message_time = entry.nsec();
+    }
+  }
+  android_logger_list_close(logger);
+  last_time = last_message_time;
+}
 #endif
 
 TEST(malloc_stress, multiple_threads_forever) {
@@ -45,6 +93,8 @@
 #endif
   uint64_t mallinfo_min = UINT64_MAX;
   uint64_t mallinfo_max = 0;
+
+  uint64_t last_message_time = 0;
   for (size_t i = 0; ; i++) {
     printf("Pass %zu\n", i);
 
@@ -74,8 +124,8 @@
     uint64_t rss_bytes = 0;
     uint64_t vss_bytes = 0;
     for (auto& vma : maps) {
-      if (vma.name == "[anon:libc_malloc]" || android::base::StartsWith(vma.name, "[anon:scudo:") ||
-          android::base::StartsWith(vma.name, "[anon:GWP-ASan")) {
+      if (vma.name == "[anon:libc_malloc]" || vma.name.starts_with("[anon:scudo:") ||
+          vma.name.starts_with("[anon:GWP-ASan")) {
         android::meminfo::Vma update_vma(vma);
         ASSERT_TRUE(proc_mem.FillInVmaStats(update_vma));
         rss_bytes += update_vma.usage.rss;
@@ -112,5 +162,15 @@
     printf("Allocated memory %zu %0.2fMB\n", mallinfo_bytes, mallinfo_bytes / (1024.0 * 1024.0));
     printf("  Min %" PRIu64 " %0.2fMB\n", mallinfo_min, mallinfo_min / (1024.0 * 1024.0));
     printf("  Max %" PRIu64 " %0.2fMB\n", mallinfo_max, mallinfo_max / (1024.0 * 1024.0));
+
+#if defined(__BIONIC__)
+    if (((i + 1) % 100) == 0) {
+      // Send native allocator stats to the log
+      mallopt(M_LOG_STATS, 0);
+
+      printf("Log stats:\n");
+      PrintLogStats(last_message_time);
+    }
+#endif
   }
 }
diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
index 2bf755b..7223784 100644
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -45,6 +45,7 @@
 #include <android-base/test_utils.h>
 
 #include "private/bionic_constants.h"
+#include "private/bionic_time_conversions.h"
 #include "SignalUtils.h"
 #include "utils.h"
 
@@ -2437,23 +2438,25 @@
   ts.tv_sec = -1;
   ASSERT_EQ(ETIMEDOUT, lock_function(&m, &ts));
 
-  // check we wait long enough for the lock.
+  // Check we wait long enough for the lock before timing out...
+
+  // What time is it before we start?
   ASSERT_EQ(0, clock_gettime(clock, &ts));
-  const int64_t start_ns = ts.tv_sec * NS_PER_S + ts.tv_nsec;
-
-  // add a second to get deadline.
+  const int64_t start_ns = to_ns(ts);
+  // Add a second to get deadline, and wait until we time out.
   ts.tv_sec += 1;
-
   ASSERT_EQ(ETIMEDOUT, lock_function(&m, &ts));
 
+  // What time is it now we've timed out?
+  timespec ts2;
+  clock_gettime(clock, &ts2);
+  const int64_t end_ns = to_ns(ts2);
+
   // The timedlock must have waited at least 1 second before returning.
-  clock_gettime(clock, &ts);
-  const int64_t end_ns = ts.tv_sec * NS_PER_S + ts.tv_nsec;
-  ASSERT_GT(end_ns - start_ns, NS_PER_S);
+  ASSERT_GE(end_ns - start_ns, NS_PER_S);
 
   // If the mutex is unlocked, pthread_mutex_timedlock should succeed.
   ASSERT_EQ(0, pthread_mutex_unlock(&m));
-
   ASSERT_EQ(0, clock_gettime(clock, &ts));
   ts.tv_sec += 1;
   ASSERT_EQ(0, lock_function(&m, &ts));
@@ -2474,12 +2477,19 @@
 #endif  // __BIONIC__
 }
 
-TEST(pthread, pthread_mutex_clocklock) {
+TEST(pthread, pthread_mutex_clocklock_MONOTONIC) {
 #if defined(__BIONIC__)
   pthread_mutex_timedlock_helper(
       CLOCK_MONOTONIC, [](pthread_mutex_t* __mutex, const timespec* __timeout) {
         return pthread_mutex_clocklock(__mutex, CLOCK_MONOTONIC, __timeout);
       });
+#else   // __BIONIC__
+  GTEST_SKIP() << "pthread_mutex_clocklock not available";
+#endif  // __BIONIC__
+}
+
+TEST(pthread, pthread_mutex_clocklock_REALTIME) {
+#if defined(__BIONIC__)
   pthread_mutex_timedlock_helper(
       CLOCK_REALTIME, [](pthread_mutex_t* __mutex, const timespec* __timeout) {
         return pthread_mutex_clocklock(__mutex, CLOCK_REALTIME, __timeout);
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 289a483..502405f 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -740,12 +740,8 @@
     // Set the second half of ptr to the expected pattern in ptr2.
     memset(state.ptr + state.MAX_LEN, '\1', state.MAX_LEN);
     memcpy(state.ptr + state.MAX_LEN, state.ptr1, copy_len);
-    size_t expected_end;
     if (copy_len > ptr1_len) {
       memset(state.ptr + state.MAX_LEN + ptr1_len, '\0', copy_len - ptr1_len);
-      expected_end = ptr1_len;
-    } else {
-      expected_end = copy_len;
     }
 
     ASSERT_EQ(state.ptr2, strncpy(state.ptr2, state.ptr1, copy_len));
diff --git a/tests/sys_time_test.cpp b/tests/sys_time_test.cpp
index ff9271f..b0e52aa 100644
--- a/tests/sys_time_test.cpp
+++ b/tests/sys_time_test.cpp
@@ -23,6 +23,7 @@
 
 #include <android-base/file.h>
 
+#include "private/bionic_time_conversions.h"
 #include "utils.h"
 
 // http://b/11383777
@@ -147,14 +148,6 @@
   ASSERT_EQ(0, syscall(__NR_gettimeofday, &tv2, nullptr));
 
   // What's the difference between the two?
-  tv2.tv_sec -= tv1.tv_sec;
-  tv2.tv_usec -= tv1.tv_usec;
-  if (tv2.tv_usec < 0) {
-    --tv2.tv_sec;
-    tv2.tv_usec += 1000000;
-  }
-
   // To try to avoid flakiness we'll accept answers within 10,000us (0.01s).
-  ASSERT_EQ(0, tv2.tv_sec);
-  ASSERT_LT(tv2.tv_usec, 10'000);
+  ASSERT_LT(to_us(tv2) - to_us(tv1), 10'000);
 }