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      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 "libc_init_common.h"
     50 #include "pthread_internal.h"
     51 
     52 #include "private/bionic_tls.h"
     53 #include "private/KernelArgumentBlock.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 
     62 extern "C" int __cxa_atexit(void (*)(void *), void *, void *);
     63 
     64 static void call_array(void(**list)()) {
     65   // First element is -1, list is null-terminated
     66   while (*++list) {
     67     (*list)();
     68   }
     69 }
     70 
     71 static void apply_gnu_relro() {
     72   ElfW(Phdr)* phdr_start = reinterpret_cast<ElfW(Phdr)*>(getauxval(AT_PHDR));
     73   unsigned long int phdr_ct = getauxval(AT_PHNUM);
     74 
     75   for (ElfW(Phdr)* phdr = phdr_start; phdr < (phdr_start + phdr_ct); phdr++) {
     76     if (phdr->p_type != PT_GNU_RELRO) {
     77       continue;
     78     }
     79 
     80     ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr);
     81     ElfW(Addr) seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz);
     82 
     83     // Check return value here? What do we do if we fail?
     84     mprotect(reinterpret_cast<void*>(seg_page_start), seg_page_end - seg_page_start, PROT_READ);
     85   }
     86 }
     87 
     88 __noreturn void __libc_init(void* raw_args,
     89                             void (*onexit)(void) __unused,
     90                             int (*slingshot)(int, char**, char**),
     91                             structors_array_t const * const structors) {
     92   KernelArgumentBlock args(raw_args);
     93   __libc_init_tls(args);
     94   __libc_init_AT_SECURE(args);
     95   __libc_init_common(args);
     96 
     97   apply_gnu_relro();
     98 
     99   // Several Linux ABIs don't pass the onexit pointer, and the ones that
    100   // do never use it.  Therefore, we ignore it.
    101 
    102   call_array(structors->preinit_array);
    103   call_array(structors->init_array);
    104 
    105   // The executable may have its own destructors listed in its .fini_array
    106   // so we need to ensure that these are called when the program exits
    107   // normally.
    108   if (structors->fini_array != NULL) {
    109     __cxa_atexit(__libc_fini,structors->fini_array,NULL);
    110   }
    111 
    112   exit(slingshot(args.argc, args.argv, args.envp));
    113 }
    114