text: /*
   * 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().
  //
  //  - TLS_SLOT_APP: Available for use by apps in Android Q and later. (This slot
  //    was used for errno in P and earlier.)
  
  #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
  #define TLS_SLOT_APP              2 // was historically used for 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
  
  // The maximum slot is fixed by the minimum TLS alignment in Bionic executables.
  #define MAX_TLS_SLOT              7
  
  #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
  #define TLS_SLOT_APP              2 // was historically used for 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_DTV              8
  #define TLS_SLOT_BIONIC_TLS       9
  #define MAX_TLS_SLOT              9 // update this value when reserving a slot
  
  #endif
  
  #define BIONIC_TLS_SLOTS (MAX_TLS_SLOT - MIN_TLS_SLOT + 1)
  