1 /* 2 * Copyright (C) 2018 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #pragma once 30 31 /** WARNING WARNING WARNING 32 ** 33 ** This header file is *NOT* part of the public Bionic ABI/API and should not 34 ** be used/included by user-serviceable parts of the system (e.g. 35 ** applications). 36 ** 37 ** It is only provided here for the benefit of Android components that need a 38 ** pre-allocated slot for performance reasons (including ART, the OpenGL 39 ** subsystem, and sanitizers). 40 **/ 41 42 // Bionic TCB / TLS slots: 43 // 44 // - TLS_SLOT_SELF: On x86-{32,64}, the kernel makes TLS memory available via 45 // the gs/fs segments. To get the address of a TLS variable, the first slot 46 // of TLS memory (accessed using %gs:0 / %fs:0) holds the address of the 47 // gs/fs segment. This slot is used by: 48 // - OpenGL and compiler-rt 49 // - Accesses of x86 ELF TLS variables 50 // 51 // - TLS_SLOT_OPENGL and TLS_SLOT_OPENGL_API: These two aren't used by bionic 52 // itself, but allow the graphics code to access TLS directly rather than 53 // using the pthread API. 54 // 55 // - TLS_SLOT_STACK_GUARD: Used for -fstack-protector by: 56 // - Clang targeting Android/arm64 57 // - gcc targeting Linux/x86-{32,64} 58 // 59 // - TLS_SLOT_SANITIZER: Lets sanitizers avoid using pthread_getspecific for 60 // finding the current thread state. 61 // 62 // - TLS_SLOT_DTV: Pointer to ELF TLS dynamic thread vector. 63 // 64 // - TLS_SLOT_ART_THREAD_SELF: Fast storage for Thread::Current() in ART. 65 // 66 // - TLS_SLOT_BIONIC_TLS: Optimizes accesses to bionic_tls by one load versus 67 // finding it using __get_thread(). 68 // 69 // - TLS_SLOT_APP: Available for use by apps in Android Q and later. (This slot 70 // was used for errno in P and earlier.) 71 72 #if defined(__arm__) || defined(__aarch64__) 73 74 // The ARM ELF TLS ABI specifies[1] that the thread pointer points at a 2-word 75 // TCB followed by the executable's TLS segment. Both the TCB and the 76 // executable's segment are aligned according to the segment, so Bionic requires 77 // a minimum segment alignment, which effectively reserves an 8-word TCB. The 78 // ARM spec allocates the first TCB word to the DTV. 79 // 80 // [1] "Addenda to, and Errata in, the ABI for the ARM Architecture". Section 3. 81 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045e/IHI0045E_ABI_addenda.pdf 82 83 #define MIN_TLS_SLOT -1 // update this value when reserving a slot 84 #define TLS_SLOT_BIONIC_TLS -1 85 #define TLS_SLOT_DTV 0 86 #define TLS_SLOT_THREAD_ID 1 87 #define TLS_SLOT_APP 2 // was historically used for errno 88 #define TLS_SLOT_OPENGL 3 89 #define TLS_SLOT_OPENGL_API 4 90 #define TLS_SLOT_STACK_GUARD 5 91 #define TLS_SLOT_SANITIZER 6 // was historically used for dlerror 92 #define TLS_SLOT_ART_THREAD_SELF 7 93 94 // The maximum slot is fixed by the minimum TLS alignment in Bionic executables. 95 #define MAX_TLS_SLOT 7 96 97 #elif defined(__i386__) || defined(__x86_64__) 98 99 // x86 uses variant 2 ELF TLS layout, which places the executable's TLS segment 100 // immediately before the thread pointer. New slots are allocated at positive 101 // offsets from the thread pointer. 102 103 #define MIN_TLS_SLOT 0 104 105 #define TLS_SLOT_SELF 0 106 #define TLS_SLOT_THREAD_ID 1 107 #define TLS_SLOT_APP 2 // was historically used for errno 108 #define TLS_SLOT_OPENGL 3 109 #define TLS_SLOT_OPENGL_API 4 110 #define TLS_SLOT_STACK_GUARD 5 111 #define TLS_SLOT_SANITIZER 6 // was historically used for dlerror 112 #define TLS_SLOT_ART_THREAD_SELF 7 113 #define TLS_SLOT_DTV 8 114 #define TLS_SLOT_BIONIC_TLS 9 115 #define MAX_TLS_SLOT 9 // update this value when reserving a slot 116 117 #endif 118 119 #define BIONIC_TLS_SLOTS (MAX_TLS_SLOT - MIN_TLS_SLOT + 1) 120