diff --git a/libc/bionic/system_property_set.cpp b/libc/bionic/system_property_set.cpp
index 6e49bce..73cf151 100644
--- a/libc/bionic/system_property_set.cpp
+++ b/libc/bionic/system_property_set.cpp
@@ -257,6 +257,21 @@
   }
 }
 
+static const char* __prop_error_to_string(int error) {
+  switch (error) {
+  case PROP_ERROR_READ_CMD: return "PROP_ERROR_READ_CMD";
+  case PROP_ERROR_READ_DATA: return "PROP_ERROR_READ_DATA";
+  case PROP_ERROR_READ_ONLY_PROPERTY: return "PROP_ERROR_READ_ONLY_PROPERTY";
+  case PROP_ERROR_INVALID_NAME: return "PROP_ERROR_INVALID_NAME";
+  case PROP_ERROR_INVALID_VALUE: return "PROP_ERROR_INVALID_VALUE";
+  case PROP_ERROR_PERMISSION_DENIED: return "PROP_ERROR_PERMISSION_DENIED";
+  case PROP_ERROR_INVALID_CMD: return "PROP_ERROR_INVALID_CMD";
+  case PROP_ERROR_HANDLE_CONTROL_MESSAGE: return "PROP_ERROR_HANDLE_CONTROL_MESSAGE";
+  case PROP_ERROR_SET_FAILED: return "PROP_ERROR_SET_FAILED";
+  }
+  return "<unknown>";
+}
+
 __BIONIC_WEAK_FOR_NATIVE_BRIDGE
 int __system_property_set(const char* key, const char* value) {
   if (key == nullptr) return -1;
@@ -310,8 +325,8 @@
 
     if (result != PROP_SUCCESS) {
       async_safe_format_log(ANDROID_LOG_WARN, "libc",
-                            "Unable to set property \"%s\" to \"%s\": error code: 0x%x", key, value,
-                            result);
+                            "Unable to set property \"%s\" to \"%s\": %s (0x%x)", key, value,
+                            __prop_error_to_string(result), result);
       return -1;
     }
 
diff --git a/libc/include/android/versioning.h b/libc/include/android/versioning.h
index c5adc02..cd61f33 100644
--- a/libc/include/android/versioning.h
+++ b/libc/include/android/versioning.h
@@ -20,15 +20,15 @@
 // we should only annotate headers when we are running versioner.
 #if defined(__BIONIC_VERSIONER)
 
-#define __INTRODUCED_IN(api_level) __attribute__((annotate("introduced_in=" #api_level)))
-#define __INTRODUCED_IN_NO_GUARD_FOR_NDK(api_level) __attribute__((annotate("introduced_in=" #api_level))) __VERSIONER_NO_GUARD
-#define __DEPRECATED_IN(api_level) __attribute__((annotate("deprecated_in=" #api_level)))
-#define __REMOVED_IN(api_level) __attribute__((annotate("obsoleted_in=" #api_level)))
-#define __INTRODUCED_IN_32(api_level) __attribute__((annotate("introduced_in_32=" #api_level)))
-#define __INTRODUCED_IN_64(api_level) __attribute__((annotate("introduced_in_64=" #api_level)))
+#define __INTRODUCED_IN(api_level) __attribute__((__annotate__("introduced_in=" #api_level)))
+#define __INTRODUCED_IN_NO_GUARD_FOR_NDK(api_level) __attribute__((__annotate__("introduced_in=" #api_level))) __VERSIONER_NO_GUARD
+#define __DEPRECATED_IN(api_level) __attribute__((__annotate__("deprecated_in=" #api_level)))
+#define __REMOVED_IN(api_level) __attribute__((__annotate__("obsoleted_in=" #api_level)))
+#define __INTRODUCED_IN_32(api_level) __attribute__((__annotate__("introduced_in_32=" #api_level)))
+#define __INTRODUCED_IN_64(api_level) __attribute__((__annotate__("introduced_in_64=" #api_level)))
 
-#define __VERSIONER_NO_GUARD __attribute__((annotate("versioner_no_guard")))
-#define __VERSIONER_FORTIFY_INLINE __attribute__((annotate("versioner_fortify_inline")))
+#define __VERSIONER_NO_GUARD __attribute__((__annotate__("versioner_no_guard")))
+#define __VERSIONER_FORTIFY_INLINE __attribute__((__annotate__("versioner_fortify_inline")))
 
 #else
 
diff --git a/libc/include/bits/stdatomic.h b/libc/include/bits/stdatomic.h
index bd94b2d..8df86e2 100644
--- a/libc/include/bits/stdatomic.h
+++ b/libc/include/bits/stdatomic.h
@@ -138,11 +138,11 @@
  * 7.17.4 Fences.
  */
 
-static inline void atomic_thread_fence(memory_order __order __attribute__((unused))) {
+static inline void atomic_thread_fence(memory_order __order __attribute__((__unused__))) {
 	__c11_atomic_thread_fence(__order);
 }
 
-static inline void atomic_signal_fence(memory_order __order __attribute__((unused))) {
+static inline void atomic_signal_fence(memory_order __order __attribute__((__unused__))) {
 	__c11_atomic_signal_fence(__order);
 }
 
diff --git a/libc/include/bits/struct_file.h b/libc/include/bits/struct_file.h
index abbd320..8cb8d28 100644
--- a/libc/include/bits/struct_file.h
+++ b/libc/include/bits/struct_file.h
@@ -39,6 +39,6 @@
 #else
   char __private[84];
 #endif
-} __attribute__((aligned(sizeof(void*))));
+} __attribute__((__aligned__(sizeof(void*))));
 
 __END_DECLS
diff --git a/libc/include/limits.h b/libc/include/limits.h
index 80fc45d..e1f566c 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -148,9 +148,15 @@
 
 /* >= _POSIX_THREAD_DESTRUCTOR_ITERATIONS */
 #define PTHREAD_DESTRUCTOR_ITERATIONS 4
-/* >= _POSIX_THREAD_KEYS_MAX */
+
+/**
+ * The number of calls to pthread_key_create() without intervening calls to
+ * pthread_key_delete() that are guaranteed to succeed. See pthread_key_create()
+ * for more details and ways to avoid hitting this limit.
+ */
 #define PTHREAD_KEYS_MAX 128
-/* bionic has no specific limit */
+
+/** bionic has no specific limit on the number of threads. */
 #undef PTHREAD_THREADS_MAX
 
 #endif /* !_LIMITS_H_ */
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 871c62c..ef41e2d 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -174,7 +174,29 @@
 
 int pthread_join(pthread_t __pthread, void* _Nullable * _Nullable __return_value_ptr);
 
+/**
+ * [pthread_key_create(3)](https://man7.org/linux/man-pages/man3/pthread_key_create.3p.html)
+ * creates a key for thread-specific data.
+ *
+ * There is a limit of `PTHREAD_KEYS_MAX` keys per process, but most callers
+ * should just use the C or C++ `thread_local` storage specifier anyway. When
+ * targeting new enough OS versions, the compiler will automatically use
+ * ELF TLS; when targeting old OS versions the emutls implementation will
+ * multiplex pthread keys behind the scenes, using one per library rather than
+ * one per thread-local variable. If you are implementing the runtime for a
+ * different language, you should consider similar implementation choices and
+ * avoid a direct one-to-one mapping from thread locals to pthread keys.
+ *
+ * Returns 0 on success and returns an error number on failure.
+ */
 int pthread_key_create(pthread_key_t* _Nonnull __key_ptr, void (* _Nullable __key_destructor)(void* _Nullable));
+
+/**
+ * [pthread_key_delete(3)](https://man7.org/linux/man-pages/man3/pthread_key_delete.3p.html)
+ * deletes a key for thread-specific data.
+ *
+ * Returns 0 on success and returns an error number on failure.
+ */
 int pthread_key_delete(pthread_key_t __key);
 
 int pthread_mutexattr_destroy(pthread_mutexattr_t* _Nonnull __attr);
diff --git a/libc/include/signal.h b/libc/include/signal.h
index cf83db8..9d47bcc 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -86,17 +86,17 @@
 int sigwait64(const sigset64_t* _Nonnull __set, int* _Nonnull __signal) __INTRODUCED_IN(28);
 
 int sighold(int __signal)
-  __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")))
+  __attribute__((__deprecated__("use sigprocmask() or pthread_sigmask() instead")))
   __INTRODUCED_IN(26);
 int sigignore(int __signal)
-  __attribute__((deprecated("use sigaction() instead"))) __INTRODUCED_IN(26);
+  __attribute__((__deprecated__("use sigaction() instead"))) __INTRODUCED_IN(26);
 int sigpause(int __signal)
-  __attribute__((deprecated("use sigsuspend() instead"))) __INTRODUCED_IN(26);
+  __attribute__((__deprecated__("use sigsuspend() instead"))) __INTRODUCED_IN(26);
 int sigrelse(int __signal)
-  __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")))
+  __attribute__((__deprecated__("use sigprocmask() or pthread_sigmask() instead")))
   __INTRODUCED_IN(26);
 sighandler_t _Nonnull sigset(int __signal, sighandler_t _Nullable __handler)
-  __attribute__((deprecated("use sigaction() instead"))) __INTRODUCED_IN(26);
+  __attribute__((__deprecated__("use sigaction() instead"))) __INTRODUCED_IN(26);
 
 int raise(int __signal);
 int kill(pid_t __pid, int __signal);
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 312b356..32264d6 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -141,7 +141,7 @@
 
 #if (defined(__STDC_VERSION__) && __STDC_VERSION__ < 201112L) || \
     (defined(__cplusplus) && __cplusplus <= 201103L)
-char* _Nullable gets(char* _Nonnull __buf) __attribute__((deprecated("gets is unsafe, use fgets instead")));
+char* _Nullable gets(char* _Nonnull __buf) __attribute__((__deprecated__("gets is unsafe, use fgets instead")));
 #endif
 int sprintf(char* __BIONIC_COMPLICATED_NULLNESS __s, const char* _Nonnull __fmt, ...)
     __printflike(2, 3) __warnattr_strict("sprintf is often misused; please use snprintf");
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 2830a49..506ab43 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -57,7 +57,7 @@
 int clearenv(void);
 
 char* _Nullable mkdtemp(char* _Nonnull __template);
-char* _Nullable mktemp(char* _Nonnull __template) __attribute__((deprecated("mktemp is unsafe, use mkstemp or tmpfile instead")));
+char* _Nullable mktemp(char* _Nonnull __template) __attribute__((__deprecated__("mktemp is unsafe, use mkstemp or tmpfile instead")));
 
 int mkostemp64(char* _Nonnull __template, int __flags) __INTRODUCED_IN(23);
 int mkostemp(char* _Nonnull __template, int __flags) __INTRODUCED_IN(23);
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index e587fe7..3218d15 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -139,12 +139,12 @@
 
 #define __wur __attribute__((__warn_unused_result__))
 
-#define __errorattr(msg) __attribute__((unavailable(msg)))
-#define __warnattr(msg) __attribute__((deprecated(msg)))
-#define __warnattr_real(msg) __attribute__((deprecated(msg)))
-#define __enable_if(cond, msg) __attribute__((enable_if(cond, msg)))
-#define __clang_error_if(cond, msg) __attribute__((diagnose_if(cond, msg, "error")))
-#define __clang_warning_if(cond, msg) __attribute__((diagnose_if(cond, msg, "warning")))
+#define __errorattr(msg) __attribute__((__unavailable__(msg)))
+#define __warnattr(msg) __attribute__((__deprecated__(msg)))
+#define __warnattr_real(msg) __attribute__((__deprecated__(msg)))
+#define __enable_if(cond, msg) __attribute__((__enable_if__(cond, msg)))
+#define __clang_error_if(cond, msg) __attribute__((__diagnose_if__(cond, msg, "error")))
+#define __clang_warning_if(cond, msg) __attribute__((__diagnose_if__(cond, msg, "warning")))
 
 #if defined(ANDROID_STRICT)
 /*
@@ -248,7 +248,7 @@
 
 #if defined(__BIONIC_FORTIFY)
 #  define __bos0(s) __bosn((s), 0)
-#  define __pass_object_size_n(n) __attribute__((pass_object_size(n)))
+#  define __pass_object_size_n(n) __attribute__((__pass_object_size__(n)))
 /*
  * FORTIFY'ed functions all have either enable_if or pass_object_size, which
  * makes taking their address impossible. Saying (&read)(foo, bar, baz); will
@@ -260,7 +260,7 @@
  * them available externally. FORTIFY'ed functions try to be as close to possible as 'invisible';
  * having stack protectors detracts from that (b/182948263).
  */
-#  define __BIONIC_FORTIFY_INLINE static inline __attribute__((no_stack_protector)) \
+#  define __BIONIC_FORTIFY_INLINE static inline __attribute__((__no_stack_protector__)) \
       __always_inline __VERSIONER_FORTIFY_INLINE
 /*
  * We should use __BIONIC_FORTIFY_VARIADIC instead of __BIONIC_FORTIFY_INLINE
@@ -270,7 +270,7 @@
  */
 #  define __BIONIC_FORTIFY_VARIADIC static inline
 /* Error functions don't have bodies, so they can just be static. */
-#  define __BIONIC_ERROR_FUNCTION_VISIBILITY static __attribute__((unused))
+#  define __BIONIC_ERROR_FUNCTION_VISIBILITY static __attribute__((__unused__))
 #else
 /* Further increase sharing for some inline functions */
 #  define __pass_object_size_n(n)
@@ -300,21 +300,21 @@
 #  define __BIONIC_INCLUDE_FORTIFY_HEADERS 1
 #endif
 
-#define __overloadable __attribute__((overloadable))
+#define __overloadable __attribute__((__overloadable__))
 
-#define __diagnose_as_builtin(...) __attribute__((diagnose_as_builtin(__VA_ARGS__)))
+#define __diagnose_as_builtin(...) __attribute__((__diagnose_as_builtin__(__VA_ARGS__)))
 
 /* Used to tag non-static symbols that are private and never exposed by the shared library. */
-#define __LIBC_HIDDEN__ __attribute__((visibility("hidden")))
+#define __LIBC_HIDDEN__ __attribute__((__visibility__("hidden")))
 
 /*
  * Used to tag symbols that should be hidden for 64-bit,
  * but visible to preserve binary compatibility for LP32.
  */
 #ifdef __LP64__
-#define __LIBC32_LEGACY_PUBLIC__ __attribute__((visibility("hidden")))
+#define __LIBC32_LEGACY_PUBLIC__ __attribute__((__visibility__("hidden")))
 #else
-#define __LIBC32_LEGACY_PUBLIC__ __attribute__((visibility("default")))
+#define __LIBC32_LEGACY_PUBLIC__ __attribute__((__visibility__("default")))
 #endif
 
 /* Used to rename functions so that the compiler emits a call to 'x' rather than the function this was applied to. */
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index c69db61..2732214 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -350,8 +350,11 @@
 int daemon(int __no_chdir, int __no_close);
 
 #if defined(__arm__)
+/**
+ * New code should use __builtin___clear_cache() instead, which works on
+ * all architectures.
+ */
 int cacheflush(long __addr, long __nbytes, long __cache);
-    /* __attribute__((deprecated("use __builtin___clear_cache instead"))); */
 #endif
 
 pid_t tcgetpgrp(int __fd);
diff --git a/libc/system_properties/system_properties.cpp b/libc/system_properties/system_properties.cpp
index 9dd5e35..1dedb61 100644
--- a/libc/system_properties/system_properties.cpp
+++ b/libc/system_properties/system_properties.cpp
@@ -120,14 +120,18 @@
     return false;
   }
 
-  auto* appcompat_contexts = new (appcompat_override_contexts_data_) ContextsSerialized();
   appcompat_filename_ = PropertiesFilename(properties_filename_.c_str(), "appcompat_override");
-  if (!appcompat_contexts->Initialize(true, appcompat_filename_.c_str(), fsetxattr_failed,
-                                      load_default_path)) {
-    appcompat_override_contexts_ = nullptr;
-    return false;
+  appcompat_override_contexts_ = nullptr;
+  if (access(appcompat_filename_.c_str(), F_OK) != -1) {
+    auto* appcompat_contexts = new (appcompat_override_contexts_data_) ContextsSerialized();
+    if (!appcompat_contexts->Initialize(true, appcompat_filename_.c_str(), fsetxattr_failed,
+                                        load_default_path)) {
+      // The appcompat folder exists, but initializing it failed
+      return false;
+    } else {
+      appcompat_override_contexts_ = appcompat_contexts;
+    }
   }
-  appcompat_override_contexts_ = appcompat_contexts;
 
   initialized_ = true;
   return true;
diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
index 77769f5..089eceb 100644
--- a/linker/linker_main.cpp
+++ b/linker/linker_main.cpp
@@ -29,6 +29,7 @@
 #include "linker_main.h"
 
 #include <link.h>
+#include <stdlib.h>
 #include <sys/auxv.h>
 
 #include "linker.h"
@@ -220,14 +221,10 @@
     exe_path = arg_path;
   }
 
-  // Path might be a symlink
+  // Path might be a symlink; we need the target so that we get the right
+  // linker configuration later.
   char sym_path[PATH_MAX];
-  ssize_t sym_path_len = readlink(exe_path, sym_path, sizeof(sym_path));
-  if (sym_path_len > 0 && sym_path_len < static_cast<ssize_t>(sizeof(sym_path))) {
-    result.path = std::string(sym_path, sym_path_len);
-  } else {
-    result.path = std::string(exe_path, strlen(exe_path));
-  }
+  result.path = std::string(realpath(exe_path, sym_path) != nullptr ? sym_path : exe_path);
 
   result.phdr = reinterpret_cast<const ElfW(Phdr)*>(getauxval(AT_PHDR));
   result.phdr_count = getauxval(AT_PHNUM);