clone.cpp revision fa9e16efaf0e885f6044e725eb759ef6de10f7ef 
1/*
2 * Copyright (C) 2010 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#define __GNU_SOURCE 1
30#include <sched.h>
31#include <stdlib.h>
32#include <stdarg.h>
33
34#include "pthread_internal.h"
35
36extern "C" pid_t __bionic_clone(uint32_t flags, void* child_stack, int* parent_tid, void* tls, int* child_tid, int (*fn)(void*), void* arg);
37extern "C" __noreturn void __exit(int status);
38
39// Called from the __bionic_clone assembler to call the thread function then exit.
40extern "C" __LIBC_HIDDEN__ void __start_thread(int (*fn)(void*), void* arg) {
41  int status = (*fn)(arg);
42  __exit(status);
43}
44
45int clone(int (*fn)(void*), void* child_stack, int flags, void* arg, ...) {
46  int* parent_tid = NULL;
47  void* new_tls = NULL;
48  int* child_tid = NULL;
49
50  // Extract any optional parameters required by the flags.
51  va_list args;
52  va_start(args, arg);
53  if ((flags & (CLONE_PARENT_SETTID|CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
54    parent_tid = va_arg(args, int*);
55  }
56  if ((flags & (CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
57    new_tls = va_arg(args, void*);
58  }
59  if ((flags & (CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
60    child_tid = va_arg(args, int*);
61  }
62  va_end(args);
63
64  // Align 'child_stack' to 16 bytes.
65  uintptr_t child_stack_addr = reinterpret_cast<uintptr_t>(child_stack);
66  child_stack_addr &= ~0xf;
67  child_stack = reinterpret_cast<void*>(child_stack_addr);
68
69  // Remember the parent pid and invalidate the cached value while we clone.
70  pthread_internal_t* self = __get_thread();
71  pid_t parent_pid = self->invalidate_cached_pid();
72
73  // Actually do the clone.
74  int clone_result = __bionic_clone(flags, child_stack, parent_tid, new_tls, child_tid, fn, arg);
75
76  // We're the parent, so put our known pid back in place.
77  // We leave the child without a cached pid, but:
78  // 1. pthread_create gives its children their own pthread_internal_t with the correct pid.
79  // 2. fork makes a clone system call directly.
80  // If any other cases become important, we could use a double trampoline like __pthread_start.
81  self->set_cached_pid(parent_pid);
82  return clone_result;
83}
84