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 * libc_init_static.c 30 * 31 * The program startup function __libc_init() defined here is 32 * used for static executables only (i.e. those that don't depend 33 * on shared libraries). It is called from arch-$ARCH/bionic/crtbegin_static.S 34 * which is directly invoked by the kernel when the program is launched. 35 * 36 * The 'structors' parameter contains pointers to various initializer 37 * arrays that must be run before the program's 'main' routine is launched. 38 */ 39 40#include <elf.h> 41#include <errno.h> 42#include <stddef.h> 43#include <stdint.h> 44#include <stdio.h> 45#include <stdlib.h> 46#include <sys/auxv.h> 47#include <sys/mman.h> 48 49#include "atexit.h" 50#include "bionic_tls.h" 51#include "KernelArgumentBlock.h" 52#include "libc_init_common.h" 53#include "pthread_internal.h" 54 55// Returns the address of the page containing address 'x'. 56#define PAGE_START(x) ((x) & PAGE_MASK) 57 58// Returns the address of the next page after address 'x', unless 'x' is 59// itself at the start of a page. 60#define PAGE_END(x) PAGE_START((x) + (PAGE_SIZE-1)) 61 62static void call_array(void(**list)()) { 63 // First element is -1, list is null-terminated 64 while (*++list) { 65 (*list)(); 66 } 67} 68 69static void apply_gnu_relro() { 70 Elf32_Phdr* phdr_start = reinterpret_cast<Elf32_Phdr*>(getauxval(AT_PHDR)); 71 unsigned long int phdr_ct = getauxval(AT_PHNUM); 72 73 for (Elf32_Phdr* phdr = phdr_start; phdr < (phdr_start + phdr_ct); phdr++) { 74 if (phdr->p_type != PT_GNU_RELRO) { 75 continue; 76 } 77 78 Elf32_Addr seg_page_start = PAGE_START(phdr->p_vaddr); 79 Elf32_Addr seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz); 80 81 // Check return value here? What do we do if we fail? 82 mprotect(reinterpret_cast<void*>(seg_page_start), seg_page_end - seg_page_start, PROT_READ); 83 } 84} 85 86__noreturn void __libc_init(void* raw_args, 87 void (*onexit)(void), 88 int (*slingshot)(int, char**, char**), 89 structors_array_t const * const structors) { 90 KernelArgumentBlock args(raw_args); 91 __libc_init_tls(args); 92 __libc_init_common(args); 93 94 apply_gnu_relro(); 95 96 // Several Linux ABIs don't pass the onexit pointer, and the ones that 97 // do never use it. Therefore, we ignore it. 98 99 call_array(structors->preinit_array); 100 call_array(structors->init_array); 101 102 // The executable may have its own destructors listed in its .fini_array 103 // so we need to ensure that these are called when the program exits 104 // normally. 105 if (structors->fini_array != NULL) { 106 __cxa_atexit(__libc_fini,structors->fini_array,NULL); 107 } 108 109 exit(slingshot(args.argc, args.argv, args.envp)); 110} 111