__libc_init_main_thread.cpp revision 12393862e55b9ab28dd29ae16fbdf498371726a7 
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#include "libc_init_common.h"
30
31#include "private/bionic_auxv.h"
32#include "private/bionic_globals.h"
33#include "private/KernelArgumentBlock.h"
34#include "pthread_internal.h"
35
36extern "C" int __set_tls(void* ptr);
37extern "C" int __set_tid_address(int* tid_address);
38
39// Setup for the main thread. For dynamic executables, this is called by the
40// linker _before_ libc is mapped in memory. This means that all writes to
41// globals from this function will apply to linker-private copies and will not
42// be visible from libc later on.
43//
44// Note: this function creates a pthread_internal_t for the initial thread and
45// stores the pointer in TLS, but does not add it to pthread's thread list. This
46// has to be done later from libc itself (see __libc_init_common).
47//
48// This is in a file by itself because it needs to be built with
49// -fno-stack-protector because it's responsible for setting up the main
50// thread's TLS (which stack protector relies on).
51
52void __libc_init_main_thread(KernelArgumentBlock& args) {
53  __libc_auxv = args.auxv;
54
55  static pthread_internal_t main_thread;
56
57  // The -fstack-protector implementation uses TLS, so make sure that's
58  // set up before we call any function that might get a stack check inserted.
59  __set_tls(main_thread.tls);
60
61  // Tell the kernel to clear our tid field when we exit, so we're like any other pthread.
62  // As a side-effect, this tells us our pid (which is the same as the main thread's tid).
63  main_thread.tid = __set_tid_address(&main_thread.tid);
64  main_thread.set_cached_pid(main_thread.tid);
65
66  // We don't want to free the main thread's stack even when the main thread exits
67  // because things like environment variables with global scope live on it.
68  // We also can't free the pthread_internal_t itself, since that lives on the main
69  // thread's stack rather than on the heap.
70  // The main thread has no mmap allocated space for stack or pthread_internal_t.
71  main_thread.mmap_size = 0;
72  pthread_attr_init(&main_thread.attr);
73  main_thread.attr.guard_size = 0; // The main thread has no guard page.
74  main_thread.attr.stack_size = 0; // User code should never see this; we'll compute it when asked.
75  // TODO: the main thread's sched_policy and sched_priority need to be queried.
76
77  // The TLS stack guard is set from the global, so ensure that we've initialized the global
78  // before we initialize the TLS.
79  __libc_init_global_stack_chk_guard(args);
80
81  __init_thread(&main_thread);
82  __init_tls(&main_thread);
83
84  // Store a pointer to the kernel argument block in a TLS slot to be
85  // picked up by the libc constructor.
86  main_thread.tls[TLS_SLOT_BIONIC_PREINIT] = &args;
87
88  __init_alternate_signal_stack(&main_thread);
89}
90