libc/bionic/libc_init_dynamic.cpp

/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * libc_init_dynamic.c
 *
 * This source files provides two important functions for dynamic
 * executables:
 *
 * - a C runtime initializer (__libc_preinit), which is called by
 *   the dynamic linker when libc.so is loaded. This happens before
 *   any other initializer (e.g. static C++ constructors in other
 *   shared libraries the program depends on).
 *
 * - a program launch function (__libc_init), which is called after
 *   all dynamic linking has been performed. Technically, it is called
 *   from arch-$ARCH/bionic/crtbegin_dynamic.S which is itself called
 *   by the dynamic linker after all libraries have been loaded and
 *   initialized.
 */

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <elf.h>
#include "libc_init_common.h"

#include "private/bionic_globals.h"
#include "private/bionic_macros.h"
#include "private/bionic_ssp.h"
#include "private/bionic_tls.h"
#include "private/KernelArgumentBlock.h"

extern "C" {
  extern void netdClientInit(void);
  extern int __cxa_atexit(void (*)(void *), void *, void *);
};

// Use an initializer so __libc_sysinfo will have a fallback implementation
// while .preinit_array constructors run.
#if defined(__i386__)
static __attribute__((__naked__)) void __libc_int0x80() {
  __asm__ volatile("int $0x80; ret");
}
__LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80);
#endif

// We need a helper function for __libc_preinit because compiling with LTO may
// inline functions requiring a stack protector check, but __stack_chk_guard is
// not initialized at the start of __libc_preinit. __libc_preinit_impl will run
// after __stack_chk_guard is initialized and therefore can safely have a stack
// protector.
__attribute__((noinline))
static void __libc_preinit_impl(KernelArgumentBlock& args) {
  __libc_shared_globals = args.shared_globals;

  __libc_init_globals(args);
  __libc_init_common(args);

  // Hooks for various libraries to let them know that we're starting up.
  __libc_globals.mutate(__libc_init_malloc);
  netdClientInit();
}

// We flag the __libc_preinit function as a constructor to ensure that
// its address is listed in libc.so's .init_array section.
// This ensures that the function is called by the dynamic linker as
// soon as the shared library is loaded.
// We give this constructor priority 1 because we want libc's constructor
// to run before any others (such as the jemalloc constructor), and lower
// is better (http://b/68046352).
__attribute__((constructor(1))) static void __libc_preinit() {
  // Read the kernel argument block pointer from TLS, then clear the slot so no
  // other initializer sees its value.
  void** tls = __get_tls();
  KernelArgumentBlock* args = static_cast<KernelArgumentBlock*>(tls[TLS_SLOT_BIONIC_PREINIT]);
  tls[TLS_SLOT_BIONIC_PREINIT] = nullptr;

  // The linker has initialized its copy of the global stack_chk_guard, and filled in the main
  // thread's TLS slot with that value. Initialize the local global stack guard with its value.
  __stack_chk_guard = reinterpret_cast<uintptr_t>(tls[TLS_SLOT_STACK_GUARD]);

  __libc_preinit_impl(*args);
}

// This function is called from the executable's _start entry point
// (see arch-$ARCH/bionic/crtbegin.c), which is itself called by the dynamic
// linker after it has loaded all shared libraries the executable depends on.
//
// Note that the dynamic linker has also run all constructors in the
// executable at this point.
__noreturn void __libc_init(void* raw_args,
                            void (*onexit)(void) __unused,
                            int (*slingshot)(int, char**, char**),
                            structors_array_t const * const structors) {
  BIONIC_STOP_UNWIND;

  KernelArgumentBlock args(raw_args);

  // Several Linux ABIs don't pass the onexit pointer, and the ones that
  // do never use it.  Therefore, we ignore it.

  // The executable may have its own destructors listed in its .fini_array
  // so we need to ensure that these are called when the program exits
  // normally.
  if (structors->fini_array) {
    __cxa_atexit(__libc_fini,structors->fini_array,nullptr);
  }

  exit(slingshot(args.argc - __libc_shared_globals->initial_linker_arg_count,
                 args.argv + __libc_shared_globals->initial_linker_arg_count,
                 args.envp));
}