/*
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* Copyright (C) 2018 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#pragma once
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/** WARNING WARNING WARNING
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**
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** This header file is *NOT* part of the public Bionic ABI/API and should not
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** be used/included by user-serviceable parts of the system (e.g.
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** applications).
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**
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** It is only provided here for the benefit of Android components that need a
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** pre-allocated slot for performance reasons (including ART, the OpenGL
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** subsystem, and sanitizers).
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**/
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// Bionic TCB / TLS slots:
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//
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// - TLS_SLOT_SELF: On x86-{32,64}, the kernel makes TLS memory available via
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// the gs/fs segments. To get the address of a TLS variable, the first slot
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// of TLS memory (accessed using %gs:0 / %fs:0) holds the address of the
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// gs/fs segment. This slot is used by:
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// - OpenGL and compiler-rt
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// - Accesses of x86 ELF TLS variables
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//
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// - TLS_SLOT_OPENGL and TLS_SLOT_OPENGL_API: These two aren't used by bionic
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// itself, but allow the graphics code to access TLS directly rather than
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// using the pthread API.
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//
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// - TLS_SLOT_STACK_GUARD: Used for -fstack-protector by:
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// - Clang targeting Android/arm64
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// - gcc targeting Linux/x86-{32,64}
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//
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// - TLS_SLOT_SANITIZER: Lets sanitizers avoid using pthread_getspecific for
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// finding the current thread state.
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//
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// - TLS_SLOT_DTV: Pointer to ELF TLS dynamic thread vector.
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//
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// - TLS_SLOT_ART_THREAD_SELF: Fast storage for Thread::Current() in ART.
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//
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// - TLS_SLOT_BIONIC_TLS: Optimizes accesses to bionic_tls by one load versus
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// finding it using __get_thread().
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//
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// - TLS_SLOT_APP: Available for use by apps in Android Q and later. (This slot
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// was used for errno in P and earlier.)
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#if defined(__arm__) || defined(__aarch64__)
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// The ARM ELF TLS ABI specifies[1] that the thread pointer points at a 2-word
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// TCB followed by the executable's TLS segment. Both the TCB and the
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// executable's segment are aligned according to the segment, so Bionic requires
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// a minimum segment alignment, which effectively reserves an 8-word TCB. The
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// ARM spec allocates the first TCB word to the DTV.
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//
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// [1] "Addenda to, and Errata in, the ABI for the ARM Architecture". Section 3.
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// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045e/IHI0045E_ABI_addenda.pdf
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#define MIN_TLS_SLOT -1 // update this value when reserving a slot
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#define TLS_SLOT_BIONIC_TLS -1
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#define TLS_SLOT_DTV 0
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#define TLS_SLOT_THREAD_ID 1
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#define TLS_SLOT_APP 2 // was historically used for errno
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#define TLS_SLOT_OPENGL 3
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#define TLS_SLOT_OPENGL_API 4
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#define TLS_SLOT_STACK_GUARD 5
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#define TLS_SLOT_SANITIZER 6 // was historically used for dlerror
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#define TLS_SLOT_ART_THREAD_SELF 7
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// The maximum slot is fixed by the minimum TLS alignment in Bionic executables.
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#define MAX_TLS_SLOT 7
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#elif defined(__i386__) || defined(__x86_64__)
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// x86 uses variant 2 ELF TLS layout, which places the executable's TLS segment
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// immediately before the thread pointer. New slots are allocated at positive
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// offsets from the thread pointer.
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#define MIN_TLS_SLOT 0
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#define TLS_SLOT_SELF 0
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#define TLS_SLOT_THREAD_ID 1
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#define TLS_SLOT_APP 2 // was historically used for errno
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#define TLS_SLOT_OPENGL 3
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#define TLS_SLOT_OPENGL_API 4
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#define TLS_SLOT_STACK_GUARD 5
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#define TLS_SLOT_SANITIZER 6 // was historically used for dlerror
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#define TLS_SLOT_ART_THREAD_SELF 7
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#define TLS_SLOT_DTV 8
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#define TLS_SLOT_BIONIC_TLS 9
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#define MAX_TLS_SLOT 9 // update this value when reserving a slot
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#endif
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#define BIONIC_TLS_SLOTS (MAX_TLS_SLOT - MIN_TLS_SLOT + 1)
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