libc_init_dynamic.cpp revision 38778e3b6c89689bbdd01f4a52ac88f02bf59783 
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-$ARCH/bionic/crtbegin_dynamic.S which is itself called
42 *   by the dynamic linker after all libraries have been loaded and
43 *   initialized.
44 */
45
46#include <stddef.h>
47#include <stdio.h>
48#include <stdlib.h>
49#include <stdint.h>
50#include <elf.h>
51#include "libc_init_common.h"
52
53#include "private/bionic_tls.h"
54#include "private/KernelArgumentBlock.h"
55
56extern "C" {
57  extern void malloc_debug_init(void);
58  extern void malloc_debug_fini(void);
59  extern void netdClientInit(void);
60  extern int __cxa_atexit(void (*)(void *), void *, void *);
61};
62
63// We flag the __libc_preinit function as a constructor to ensure
64// that its address is listed in libc.so's .init_array section.
65// This ensures that the function is called by the dynamic linker
66// as soon as the shared library is loaded.
67__attribute__((constructor)) static void __libc_preinit() {
68  // Read the kernel argument block pointer from TLS.
69  void** tls = __get_tls();
70  KernelArgumentBlock** args_slot = &reinterpret_cast<KernelArgumentBlock**>(tls)[TLS_SLOT_BIONIC_PREINIT];
71  KernelArgumentBlock* args = *args_slot;
72
73  // Clear the slot so no other initializer sees its value.
74  // __libc_init_common() will change the TLS area so the old one won't be accessible anyway.
75  *args_slot = NULL;
76
77  __libc_init_common(*args);
78
79  // Hooks for various libraries to let them know that we're starting up.
80  malloc_debug_init();
81  netdClientInit();
82}
83
84__LIBC_HIDDEN__ void __libc_postfini() {
85  // A hook for the debug malloc library to let it know that we're shutting down.
86  malloc_debug_fini();
87}
88
89// This function is called from the executable's _start entry point
90// (see arch-$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