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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_dynamic.c
     30  *
     31  * This source files provides two important functions for dynamic
     32  * executables:
     33  *
     34  * - a C runtime initializer (__libc_preinit), which is called by
     35  *   the dynamic linker when libc.so is loaded. This happens before
     36  *   any other initializer (e.g. static C++ constructors in other
     37  *   shared libraries the program depends on).
     38  *
     39  * - a program launch function (__libc_init), which is called after
     40  *   all dynamic linking has been performed. Technically, it is called
     41  *   from arch-$ARCH/bionic/crtbegin_dynamic.S which is itself called
     42  *   by the dynamic linker after all libraries have been loaded and
     43  *   initialized.
     44  */
     45 
     46 #include <stddef.h>
     47 #include <stdio.h>
     48 #include <stdlib.h>
     49 #include <stdint.h>
     50 #include <elf.h>
     51 #include "atexit.h"
     52 #include "KernelArgumentBlock.h"
     53 #include "libc_init_common.h"
     54 #include <bionic_tls.h>
     55 
     56 extern "C" {
     57   extern void pthread_debug_init(void);
     58   extern void malloc_debug_init(void);
     59   extern void malloc_debug_fini(void);
     60 };
     61 
     62 // We flag the __libc_preinit function as a constructor to ensure
     63 // that its address is listed in libc.so's .init_array section.
     64 // This ensures that the function is called by the dynamic linker
     65 // as soon as the shared library is loaded.
     66 __attribute__((constructor)) static void __libc_preinit() {
     67   // Read the kernel argument block pointer from TLS.
     68   void* tls = const_cast<void*>(__get_tls());
     69   KernelArgumentBlock** args_slot = &reinterpret_cast<KernelArgumentBlock**>(tls)[TLS_SLOT_BIONIC_PREINIT];
     70   KernelArgumentBlock* args = *args_slot;
     71 
     72   // Clear the slot so no other initializer sees its value.
     73   // __libc_init_common() will change the TLS area so the old one won't be accessible anyway.
     74   *args_slot = NULL;
     75 
     76   __libc_init_common(*args);
     77 
     78   // Hooks for the debug malloc and pthread libraries to let them know that we're starting up.
     79   pthread_debug_init();
     80   malloc_debug_init();
     81 }
     82 
     83 __LIBC_HIDDEN__ void __libc_postfini() {
     84   // A hook for the debug malloc library to let it know that we're shutting down.
     85   malloc_debug_fini();
     86 }
     87 
     88 // This function is called from the executable's _start entry point
     89 // (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself
     90 // called by the dynamic linker after it has loaded all shared
     91 // libraries the executable depends on.
     92 //
     93 // Note that the dynamic linker has also run all constructors in the
     94 // executable at this point.
     95 __noreturn void __libc_init(void* raw_args,
     96                             void (*onexit)(void),
     97                             int (*slingshot)(int, char**, char**),
     98                             structors_array_t const * const structors) {
     99 
    100   KernelArgumentBlock args(raw_args);
    101 
    102   // Several Linux ABIs don't pass the onexit pointer, and the ones that
    103   // do never use it.  Therefore, we ignore it.
    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) {
    109     __cxa_atexit(__libc_fini,structors->fini_array,NULL);
    110   }
    111 
    112   exit(slingshot(args.argc, args.argv, args.envp));
    113 }
    114