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 /*
30 * This source files provides two important functions for dynamic
31 * executables:
32 *
33 * - a C runtime initializer (__libc_preinit), which is called by
34 * the dynamic linker when libc.so is loaded. This happens before
35 * any other initializer (e.g. static C++ constructors in other
36 * shared libraries the program depends on).
37 *
38 * - a program launch function (__libc_init), which is called after
39 * all dynamic linking has been performed.
40 */
41
42 #include <stddef.h>
43 #include <stdio.h>
44 #include <stdlib.h>
45 #include <stdint.h>
46 #include <elf.h>
47 #include "libc_init_common.h"
48
49 #include "private/bionic_defs.h"
50 #include "private/bionic_elf_tls.h"
51 #include "private/bionic_globals.h"
52 #include "platform/bionic/macros.h"
53 #include "private/bionic_ssp.h"
54 #include "private/bionic_tls.h"
55 #include "private/KernelArgumentBlock.h"
56
57 extern "C" {
58 extern void netdClientInit(void);
59 extern int __cxa_atexit(void (*)(void *), void *, void *);
60 };
61
62 // Use an initializer so __libc_sysinfo will have a fallback implementation
63 // while .preinit_array constructors run.
64 #if defined(__i386__)
65 __LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80);
66 #endif
67
68 extern "C" __attribute__((weak)) void __hwasan_library_loaded(ElfW(Addr) base,
69 const ElfW(Phdr)* phdr,
70 ElfW(Half) phnum);
71 extern "C" __attribute__((weak)) void __hwasan_library_unloaded(ElfW(Addr) base,
72 const ElfW(Phdr)* phdr,
73 ElfW(Half) phnum);
74
75 // We need a helper function for __libc_preinit because compiling with LTO may
76 // inline functions requiring a stack protector check, but __stack_chk_guard is
77 // not initialized at the start of __libc_preinit. __libc_preinit_impl will run
78 // after __stack_chk_guard is initialized and therefore can safely have a stack
79 // protector.
80 __attribute__((noinline))
__libc_preinit_impl()81 static void __libc_preinit_impl() {
82 #if defined(__i386__)
83 __libc_init_sysinfo();
84 #endif
85
86 // Register libc.so's copy of the TLS generation variable so the linker can
87 // update it when it loads or unloads a shared object.
88 TlsModules& tls_modules = __libc_shared_globals()->tls_modules;
89 tls_modules.generation_libc_so = &__libc_tls_generation_copy;
90 __libc_tls_generation_copy = tls_modules.generation;
91
92 __libc_init_globals();
93 __libc_init_common();
94 __libc_init_scudo();
95
96 // Hooks for various libraries to let them know that we're starting up.
97 __libc_globals.mutate(__libc_init_malloc);
98
99 // Install reserved signal handlers for assisting the platform's profilers.
100 __libc_init_profiling_handlers();
101
102 __libc_init_fork_handler();
103
104 #if __has_feature(hwaddress_sanitizer)
105 // Notify the HWASan runtime library whenever a library is loaded or unloaded
106 // so that it can update its shadow memory.
107 __libc_shared_globals()->load_hook = __hwasan_library_loaded;
108 __libc_shared_globals()->unload_hook = __hwasan_library_unloaded;
109 #endif
110
111 __libc_shared_globals()->set_target_sdk_version_hook = __libc_set_target_sdk_version;
112
113 netdClientInit();
114 }
115
116 // We flag the __libc_preinit function as a constructor to ensure that
117 // its address is listed in libc.so's .init_array section.
118 // This ensures that the function is called by the dynamic linker as
119 // soon as the shared library is loaded.
120 // We give this constructor priority 1 because we want libc's constructor
121 // to run before any others (such as the jemalloc constructor), and lower
122 // is better (http://b/68046352).
__libc_preinit()123 __attribute__((constructor(1))) static void __libc_preinit() {
124 // The linker has initialized its copy of the global stack_chk_guard, and filled in the main
125 // thread's TLS slot with that value. Initialize the local global stack guard with its value.
126 __stack_chk_guard = reinterpret_cast<uintptr_t>(__get_tls()[TLS_SLOT_STACK_GUARD]);
127
128 __libc_preinit_impl();
129 }
130
131 // This function is called from the executable's _start entry point
132 // (see arch-$ARCH/bionic/crtbegin.c), which is itself called by the dynamic
133 // linker after it has loaded all shared libraries the executable depends on.
134 //
135 // Note that the dynamic linker has also run all constructors in the
136 // executable at this point.
__libc_init(void * raw_args,void (* onexit)(void)__unused,int (* slingshot)(int,char **,char **),structors_array_t const * const structors)137 __noreturn void __libc_init(void* raw_args,
138 void (*onexit)(void) __unused,
139 int (*slingshot)(int, char**, char**),
140 structors_array_t const * const structors) {
141 BIONIC_STOP_UNWIND;
142
143 KernelArgumentBlock args(raw_args);
144
145 // Several Linux ABIs don't pass the onexit pointer, and the ones that
146 // do never use it. Therefore, we ignore it.
147
148 // The executable may have its own destructors listed in its .fini_array
149 // so we need to ensure that these are called when the program exits
150 // normally.
151 if (structors->fini_array) {
152 __cxa_atexit(__libc_fini,structors->fini_array,nullptr);
153 }
154
155 exit(slingshot(args.argc - __libc_shared_globals()->initial_linker_arg_count,
156 args.argv + __libc_shared_globals()->initial_linker_arg_count,
157 args.envp));
158 }
159
160 extern "C" libc_shared_globals* __loader_shared_globals();
161
__libc_shared_globals()162 __LIBC_HIDDEN__ libc_shared_globals* __libc_shared_globals() {
163 return __loader_shared_globals();
164 }
165