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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 "libc_init_common.h"
     52 
     53 #include "private/bionic_tls.h"
     54 #include "private/KernelArgumentBlock.h"
     55 
     56 extern "C" {
     57   extern void malloc_debug_init(void);
     58   extern void malloc_debug_fini(void);
     59   extern void netdClientInit(void);
     60   extern int __cxa_atexit(void (*)(void *), void *, void *);
     61 };
     62 
     63 // We flag the __libc_preinit function as a constructor to ensure
     64 // that its address is listed in libc.so's .init_array section.
     65 // This ensures that the function is called by the dynamic linker
     66 // as soon as the shared library is loaded.
     67 __attribute__((constructor)) static void __libc_preinit() {
     68   // Read the kernel argument block pointer from TLS.
     69   void** tls = __get_tls();
     70   KernelArgumentBlock** args_slot = &reinterpret_cast<KernelArgumentBlock**>(tls)[TLS_SLOT_BIONIC_PREINIT];
     71   KernelArgumentBlock* args = *args_slot;
     72 
     73   // Clear the slot so no other initializer sees its value.
     74   // __libc_init_common() will change the TLS area so the old one won't be accessible anyway.
     75   *args_slot = NULL;
     76 
     77   __libc_init_common(*args);
     78 
     79   // Hooks for various libraries to let them know that we're starting up.
     80   malloc_debug_init();
     81   netdClientInit();
     82 }
     83 
     84 __LIBC_HIDDEN__ void __libc_postfini() {
     85   // A hook for the debug malloc library to let it know that we're shutting down.
     86   malloc_debug_fini();
     87 }
     88 
     89 // This function is called from the executable's _start entry point
     90 // (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself
     91 // called by the dynamic linker after it has loaded all shared
     92 // libraries the executable depends on.
     93 //
     94 // Note that the dynamic linker has also run all constructors in the
     95 // executable at this point.
     96 __noreturn void __libc_init(void* raw_args,
     97                             void (*onexit)(void) __unused,
     98                             int (*slingshot)(int, char**, char**),
     99                             structors_array_t const * const structors) {
    100 
    101   KernelArgumentBlock args(raw_args);
    102 
    103   // Several Linux ABIs don't pass the onexit pointer, and the ones that
    104   // do never use it.  Therefore, we ignore it.
    105 
    106   // The executable may have its own destructors listed in its .fini_array
    107   // so we need to ensure that these are called when the program exits
    108   // normally.
    109   if (structors->fini_array) {
    110     __cxa_atexit(__libc_fini,structors->fini_array,NULL);
    111   }
    112 
    113   exit(slingshot(args.argc, args.argv, args.envp));
    114 }
    115