diff --git a/libc/private/bionic_asm_tls.h b/libc/private/bionic_asm_tls.h
new file mode 100644
index 0000000..06e3dce
--- /dev/null
+++ b/libc/private/bionic_asm_tls.h
@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2018 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
+
+/** WARNING WARNING WARNING
+ **
+ ** This header file is *NOT* part of the public Bionic ABI/API and should not
+ ** be used/included by user-serviceable parts of the system (e.g.
+ ** applications).
+ **
+ ** It is only provided here for the benefit of Android components that need a
+ ** pre-allocated slot for performance reasons (including ART, the OpenGL
+ ** subsystem, and sanitizers).
+ **/
+
+// Bionic TCB / TLS slots:
+//
+//  - TLS_SLOT_SELF: On x86-{32,64}, the kernel makes TLS memory available via
+//    the gs/fs segments. To get the address of a TLS variable, the first slot
+//    of TLS memory (accessed using %gs:0 / %fs:0) holds the address of the
+//    gs/fs segment. This slot is used by:
+//     - OpenGL and compiler-rt
+//     - Accesses of x86 ELF TLS variables
+//
+//  - TLS_SLOT_OPENGL and TLS_SLOT_OPENGL_API: These two aren't used by bionic
+//    itself, but allow the graphics code to access TLS directly rather than
+//    using the pthread API.
+//
+//  - TLS_SLOT_STACK_GUARD: Used for -fstack-protector by:
+//     - Clang targeting Android/arm64
+//     - gcc targeting Linux/x86-{32,64}
+//
+//  - TLS_SLOT_SANITIZER: Lets sanitizers avoid using pthread_getspecific for
+//    finding the current thread state.
+//
+//  - TLS_SLOT_DTV: Pointer to ELF TLS dynamic thread vector.
+//
+//  - TLS_SLOT_ART_THREAD_SELF: Fast storage for Thread::Current() in ART.
+//
+//  - TLS_SLOT_BIONIC_TLS: Optimizes accesses to bionic_tls by one load versus
+//    finding it using __get_thread().
+
+#if defined(__arm__) || defined(__aarch64__)
+
+// The ARM ELF TLS ABI specifies[1] that the thread pointer points at a 2-word
+// TCB followed by the executable's TLS segment. Both the TCB and the
+// executable's segment are aligned according to the segment, so Bionic requires
+// a minimum segment alignment, which effectively reserves an 8-word TCB. The
+// ARM spec allocates the first TCB word to the DTV.
+//
+// [1] "Addenda to, and Errata in, the ABI for the ARM Architecture". Section 3.
+// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045e/IHI0045E_ABI_addenda.pdf
+
+#define MIN_TLS_SLOT              -1 // update this value when reserving a slot
+#define TLS_SLOT_BIONIC_TLS       -1
+#define TLS_SLOT_DTV              0
+#define TLS_SLOT_THREAD_ID        1
+// Slot 2 is free (was historically used for TLS_SLOT_ERRNO)
+#define TLS_SLOT_OPENGL           3
+#define TLS_SLOT_OPENGL_API       4
+#define TLS_SLOT_STACK_GUARD      5
+#define TLS_SLOT_SANITIZER        6 // was historically used for dlerror
+#define TLS_SLOT_ART_THREAD_SELF  7
+#define TLS_SLOT_TSAN             8 // should be replaced with TLS_SLOT_SANITIZER
+
+// The maximum slot is fixed by the minimum TLS alignment in Bionic executables.
+// It should be changed to 7 once TLS_SLOT_TSAN is removed.
+#define MAX_TLS_SLOT              8
+
+#elif defined(__i386__) || defined(__x86_64__)
+
+// x86 uses variant 2 ELF TLS layout, which places the executable's TLS segment
+// immediately before the thread pointer. New slots are allocated at positive
+// offsets from the thread pointer.
+
+#define MIN_TLS_SLOT              0
+
+#define TLS_SLOT_SELF             0
+#define TLS_SLOT_THREAD_ID        1
+// Slot 2 is free (was historically used for TLS_SLOT_ERRNO)
+#define TLS_SLOT_OPENGL           3
+#define TLS_SLOT_OPENGL_API       4
+#define TLS_SLOT_STACK_GUARD      5
+#define TLS_SLOT_SANITIZER        6 // was historically used for dlerror
+#define TLS_SLOT_ART_THREAD_SELF  7
+#define TLS_SLOT_TSAN             8 // should be replaced with TLS_SLOT_SANITIZER
+#define TLS_SLOT_DTV              9
+#define TLS_SLOT_BIONIC_TLS       10
+#define MAX_TLS_SLOT              10 // update this value when reserving a slot
+
+#endif
+
+#define BIONIC_TLS_SLOTS (MAX_TLS_SLOT - MIN_TLS_SLOT + 1)
diff --git a/libc/private/bionic_elf_tls.h b/libc/private/bionic_elf_tls.h
new file mode 100644
index 0000000..e847669
--- /dev/null
+++ b/libc/private/bionic_elf_tls.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2019 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 <stdint.h>
+
+struct StaticTlsLayout {
+  constexpr StaticTlsLayout() {}
+
+private:
+  size_t offset_ = 0;
+  size_t alignment_ = 1;
+  bool overflowed_ = false;
+
+  // Offsets to various Bionic TLS structs from the beginning of static TLS.
+  size_t offset_bionic_tcb_ = SIZE_MAX;
+  size_t offset_bionic_tls_ = SIZE_MAX;
+
+public:
+  size_t offset_bionic_tcb() const { return offset_bionic_tcb_; }
+  size_t offset_bionic_tls() const { return offset_bionic_tls_; }
+
+  size_t size() const { return offset_; }
+  size_t alignment() const { return alignment_; }
+  bool overflowed() const { return overflowed_; }
+
+  void reserve_tcb();
+  void reserve_bionic_tls();
+  void finish_layout();
+
+private:
+  size_t reserve(size_t size, size_t alignment);
+
+  template <typename T> size_t reserve_type() {
+    return reserve(sizeof(T), alignof(T));
+  }
+
+  size_t round_up_with_overflow_check(size_t value, size_t alignment);
+};
diff --git a/libc/private/bionic_globals.h b/libc/private/bionic_globals.h
index ceda38a..b5e677e 100644
--- a/libc/private/bionic_globals.h
+++ b/libc/private/bionic_globals.h
@@ -33,6 +33,7 @@
 #include <link.h>
 #include <pthread.h>
 
+#include "private/bionic_elf_tls.h"
 #include "private/bionic_fdsan.h"
 #include "private/bionic_malloc_dispatch.h"
 #include "private/bionic_vdso.h"
@@ -67,6 +68,8 @@
   pthread_mutex_t abort_msg_lock = PTHREAD_MUTEX_INITIALIZER;
   abort_msg_t* abort_msg = nullptr;
 
+  StaticTlsLayout static_tls_layout;
+
   // Values passed from the linker to libc.so.
   const char* init_progname = nullptr;
   char** init_environ = nullptr;
diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index 4749cee..90914c3 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef __BIONIC_PRIVATE_BIONIC_TLS_H_
-#define __BIONIC_PRIVATE_BIONIC_TLS_H_
+#pragma once
 
 #include <locale.h>
 #include <mntent.h>
@@ -35,73 +34,48 @@
 #include <sys/cdefs.h>
 #include <sys/param.h>
 
+#include "bionic_asm_tls.h"
 #include "bionic_macros.h"
 #include "__get_tls.h"
 #include "grp_pwd.h"
 
-__BEGIN_DECLS
-
 /** WARNING WARNING WARNING
  **
- ** This header file is *NOT* part of the public Bionic ABI/API
- ** and should not be used/included by user-serviceable parts of
- ** the system (e.g. applications).
- **
- ** It is only provided here for the benefit of the system dynamic
- ** linker and the OpenGL sub-system (which needs to access the
- ** pre-allocated slot directly for performance reason).
+ ** This header file is *NOT* part of the public Bionic ABI/API and should not
+ ** be used/included by user-serviceable parts of the system (e.g.
+ ** applications).
  **/
 
-// Well-known TLS slots. What data goes in which slot is arbitrary unless otherwise noted.
-enum {
-  TLS_SLOT_SELF = 0, // The kernel requires this specific slot for x86.
-  TLS_SLOT_THREAD_ID,
+class pthread_internal_t;
 
-  // TLS slot 2 was used for errno but is now free.
+// This struct is small, so the linker can allocate a temporary copy on its
+// stack. It can't be combined with pthread_internal_t because:
+//  - native bridge requires pthread_internal_t to have the same layout across
+//    architectures, and
+//  - On x86, this struct would have to be placed at the front of
+//    pthread_internal_t, moving fields like `tid`.
+//  - We'd like to avoid having a temporary pthread_internal_t object that
+//    needs to be transferred once the final size of static TLS is known.
+struct bionic_tcb {
+  void* raw_slots_storage[BIONIC_TLS_SLOTS];
 
-  // These two aren't used by bionic itself, but allow the graphics code to
-  // access TLS directly rather than using the pthread API.
-  TLS_SLOT_OPENGL_API = 3,
-  TLS_SLOT_OPENGL = 4,
+  // Return a reference to a slot given its TP-relative TLS_SLOT_xxx index.
+  // The thread pointer (i.e. __get_tls()) points at &tls_slot(0).
+  void*& tls_slot(size_t tpindex) {
+    return raw_slots_storage[tpindex - MIN_TLS_SLOT];
+  }
 
-  TLS_SLOT_STACK_GUARD = 5, // GCC requires this specific slot for x86.
+  // Initialize the main thread's final object using its bootstrap object.
+  void copy_from_bootstrap(const bionic_tcb* boot) {
+    // Copy everything. Problematic slots will be reinitialized.
+    *this = *boot;
+  }
 
-  // Lets sanitizers avoid using pthread_getspecific for finding the current
-  // thread state. (Slot 6 was historically used for dlerror instead.)
-  TLS_SLOT_SANITIZER = 6,
-
-  // Fast storage for Thread::Current() in ART.
-  TLS_SLOT_ART_THREAD_SELF = 7,
-
-  // Lets TSAN avoid using pthread_getspecific for finding the current thread
-  // state.
-  TLS_SLOT_TSAN = 8,
-
-  BIONIC_TLS_SLOTS // Must come last!
+  pthread_internal_t* thread() {
+    return static_cast<pthread_internal_t*>(tls_slot(TLS_SLOT_THREAD_ID));
+  }
 };
 
-// ~3 pages.
-struct bionic_tls {
-  locale_t locale;
-
-  char basename_buf[MAXPATHLEN];
-  char dirname_buf[MAXPATHLEN];
-
-  mntent mntent_buf;
-  char mntent_strings[BUFSIZ];
-
-  char ptsname_buf[32];
-  char ttyname_buf[64];
-
-  char strerror_buf[NL_TEXTMAX];
-  char strsignal_buf[NL_TEXTMAX];
-
-  group_state_t group;
-  passwd_state_t passwd;
-};
-
-#define BIONIC_TLS_SIZE (__BIONIC_ALIGN(sizeof(bionic_tls), PAGE_SIZE))
-
 /*
  * Bionic uses some pthread keys internally. All pthread keys used internally
  * should be created in constructors, except for keys that may be used in or
@@ -126,12 +100,42 @@
  */
 #define BIONIC_PTHREAD_KEY_COUNT (BIONIC_PTHREAD_KEY_RESERVED_COUNT + PTHREAD_KEYS_MAX)
 
-__END_DECLS
+class pthread_key_data_t {
+ public:
+  uintptr_t seq; // Use uintptr_t just for alignment, as we use pointer below.
+  void* data;
+};
 
-#if defined(__cplusplus)
+// ~3 pages. This struct is allocated as static TLS memory (i.e. at a fixed
+// offset from the thread pointer).
+struct bionic_tls {
+  pthread_key_data_t key_data[BIONIC_PTHREAD_KEY_COUNT];
+
+  locale_t locale;
+
+  char basename_buf[MAXPATHLEN];
+  char dirname_buf[MAXPATHLEN];
+
+  mntent mntent_buf;
+  char mntent_strings[BUFSIZ];
+
+  char ptsname_buf[32];
+  char ttyname_buf[64];
+
+  char strerror_buf[NL_TEXTMAX];
+  char strsignal_buf[NL_TEXTMAX];
+
+  group_state_t group;
+  passwd_state_t passwd;
+
+  // Initialize the main thread's final object using its bootstrap object.
+  void copy_from_bootstrap(const bionic_tls* boot __attribute__((unused))) {
+    // Nothing in bionic_tls needs to be preserved in the transition to the
+    // final TLS objects, so don't copy anything.
+  }
+};
+
 class KernelArgumentBlock;
-extern void __libc_init_main_thread_early(KernelArgumentBlock& args);
-extern void __libc_init_main_thread_late();
-#endif
-
-#endif /* __BIONIC_PRIVATE_BIONIC_TLS_H_ */
+extern "C" void __libc_init_main_thread_early(const KernelArgumentBlock& args, bionic_tcb* temp_tcb);
+extern "C" void __libc_init_main_thread_late();
+extern "C" void __libc_init_main_thread_final();
diff --git a/libc/private/linker_native_bridge.h b/libc/private/linker_native_bridge.h
new file mode 100644
index 0000000..bfd0153
--- /dev/null
+++ b/libc/private/linker_native_bridge.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2019 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
+
+extern "C" void __linker_reserve_bionic_tls_in_static_tls();