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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-$ARCH/bionic/crtbegin_dynamic.S which is itself called
     42  *   by the dynamic linker after all libraries have been loaded and
     43  *   initialized.
     44  */
     45 
     46 #include <stddef.h>
     47 #include <stdio.h>
     48 #include <stdlib.h>
     49 #include <stdint.h>
     50 #include <elf.h>
     51 #include "atexit.h"
     52 #include "libc_init_common.h"
     53 #include <bionic_tls.h>
     54 
     55 /* We flag the __libc_preinit function as a constructor to ensure
     56  * that its address is listed in libc.so's .init_array section.
     57  * This ensures that the function is called by the dynamic linker
     58  * as soon as the shared library is loaded.
     59  */
     60 void __attribute__((constructor)) __libc_preinit(void);
     61 
     62 void __libc_preinit(void)
     63 {
     64     /* Read the ELF data pointer form a special slot of the
     65      * TLS area, then call __libc_init_common with it.
     66      *
     67      * Note that:
     68      * - we clear the slot so no other initializer sees its value.
     69      * - __libc_init_common() will change the TLS area so the old one
     70      *   won't be accessible anyway.
     71      */
     72     void**      tls_area = (void**)__get_tls();
     73     unsigned*   elfdata   = tls_area[TLS_SLOT_BIONIC_PREINIT];
     74 
     75     tls_area[TLS_SLOT_BIONIC_PREINIT] = NULL;
     76 
     77     __libc_init_common(elfdata);
     78 
     79     /* Setup malloc routines accordingly to the environment.
     80      * Requires system properties
     81      */
     82     extern void malloc_debug_init(void);
     83     malloc_debug_init();
     84 }
     85 
     86 /* This function is called from the executable's _start entry point
     87  * (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself
     88  * called by the dynamic linker after it has loaded all shared
     89  * libraries the executable depends on.
     90  *
     91  * Note that the dynamic linker has also run all constructors in the
     92  * executable at this point.
     93  */
     94 __noreturn void __libc_init(uintptr_t *elfdata,
     95                        void (*onexit)(void),
     96                        int (*slingshot)(int, char**, char**),
     97                        structors_array_t const * const structors)
     98 {
     99     int     argc = (int)*elfdata;
    100     char**  argv = (char**)(elfdata + 1);
    101     char**  envp = argv + argc + 1;
    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 
    107     /* The executable may have its own destructors listed in its .fini_array
    108      * so we need to ensure that these are called when the program exits
    109      * normally.
    110      */
    111     if (structors->fini_array)
    112         __cxa_atexit(__libc_fini,structors->fini_array,NULL);
    113 
    114     exit(slingshot(argc, argv, envp));
    115 }
    116