1 /* 2 * Copyright (C) 2008 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 /* 30 * libc_init_dynamic.c 31 * 32 * This source files provides two important functions for dynamic 33 * executables: 34 * 35 * - a C runtime initializer (__libc_preinit), which is called by 36 * the dynamic linker when libc.so is loaded. This happens before 37 * any other initializer (e.g. static C++ constructors in other 38 * shared libraries the program depends on). 39 * 40 * - a program launch function (__libc_init), which is called after 41 * all dynamic linking has been performed. Technically, it is called 42 * from arch-$ARCH/bionic/crtbegin_dynamic.S which is itself called 43 * by the dynamic linker after all libraries have been loaded and 44 * initialized. 45 */ 46 47 #include <stddef.h> 48 #include <stdio.h> 49 #include <stdlib.h> 50 #include <stdint.h> 51 #include <elf.h> 52 #include "libc_init_common.h" 53 54 #include "private/bionic_globals.h" 55 #include "private/bionic_macros.h" 56 #include "private/bionic_ssp.h" 57 #include "private/bionic_tls.h" 58 #include "private/KernelArgumentBlock.h" 59 60 extern "C" { 61 extern void netdClientInit(void); 62 extern int __cxa_atexit(void (*)(void *), void *, void *); 63 }; 64 65 // We need a helper function for __libc_preinit because compiling with LTO may 66 // inline functions requiring a stack protector check, but __stack_chk_guard is 67 // not initialized at the start of __libc_preinit. __libc_preinit_impl will run 68 // after __stack_chk_guard is initialized and therefore can safely have a stack 69 // protector. 70 __attribute__((noinline)) 71 static void __libc_preinit_impl(KernelArgumentBlock& args) { 72 __libc_init_globals(args); 73 __libc_init_common(args); 74 75 // Hooks for various libraries to let them know that we're starting up. 76 __libc_globals.mutate(__libc_init_malloc); 77 netdClientInit(); 78 } 79 80 // We flag the __libc_preinit function as a constructor to ensure that 81 // its address is listed in libc.so's .init_array section. 82 // This ensures that the function is called by the dynamic linker as 83 // soon as the shared library is loaded. 84 // We give this constructor priority 1 because we want libc's constructor 85 // to run before any others (such as the jemalloc constructor), and lower 86 // is better (http://b/68046352). 87 __attribute__((constructor(1))) static void __libc_preinit() { 88 // Read the kernel argument block pointer from TLS. 89 void** tls = __get_tls(); 90 KernelArgumentBlock** args_slot = &reinterpret_cast<KernelArgumentBlock**>(tls)[TLS_SLOT_BIONIC_PREINIT]; 91 KernelArgumentBlock* args = *args_slot; 92 93 // Clear the slot so no other initializer sees its value. 94 // __libc_init_common() will change the TLS area so the old one won't be accessible anyway. 95 *args_slot = NULL; 96 97 // The linker has initialized its copy of the global stack_chk_guard, and filled in the main 98 // thread's TLS slot with that value. Initialize the local global stack guard with its value. 99 __stack_chk_guard = reinterpret_cast<uintptr_t>(tls[TLS_SLOT_STACK_GUARD]); 100 101 __libc_preinit_impl(*args); 102 } 103 104 // This function is called from the executable's _start entry point 105 // (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself 106 // called by the dynamic linker after it has loaded all shared 107 // libraries the executable depends on. 108 // 109 // Note that the dynamic linker has also run all constructors in the 110 // executable at this point. 111 __noreturn void __libc_init(void* raw_args, 112 void (*onexit)(void) __unused, 113 int (*slingshot)(int, char**, char**), 114 structors_array_t const * const structors) { 115 BIONIC_STOP_UNWIND; 116 117 KernelArgumentBlock args(raw_args); 118 119 // Several Linux ABIs don't pass the onexit pointer, and the ones that 120 // do never use it. Therefore, we ignore it. 121 122 // The executable may have its own destructors listed in its .fini_array 123 // so we need to ensure that these are called when the program exits 124 // normally. 125 if (structors->fini_array) { 126 __cxa_atexit(__libc_fini,structors->fini_array,NULL); 127 } 128 129 exit(slingshot(args.argc, args.argv, args.envp)); 130 } 131 132 extern "C" uint32_t android_get_application_target_sdk_version(); 133 134 uint32_t bionic_get_application_target_sdk_version() { 135 return android_get_application_target_sdk_version(); 136 } 137
