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 #include <sys/syscall.h>
34
35 #include "pthread_internal.h"
36
37 extern "C" pid_t __bionic_clone(uint32_t flags, void* child_stack, int* parent_tid, void* tls, int* child_tid, int (*fn)(void*), void* arg);
38 extern "C" __noreturn void __exit(int status);
39
40 // Called from the __bionic_clone assembler to call the thread function then exit.
__start_thread(int (* fn)(void *),void * arg)41 extern "C" __LIBC_HIDDEN__ void __start_thread(int (*fn)(void*), void* arg) {
42 pthread_internal_t* self = __get_thread();
43 if (self && self->tid == -1) {
44 self->tid = syscall(__NR_gettid);
45 }
46
47 int status = (*fn)(arg);
48 __exit(status);
49 }
50
clone(int (* fn)(void *),void * child_stack,int flags,void * arg,...)51 int clone(int (*fn)(void*), void* child_stack, int flags, void* arg, ...) {
52 int* parent_tid = NULL;
53 void* new_tls = NULL;
54 int* child_tid = NULL;
55
56 if (fn != nullptr && child_stack == nullptr) {
57 errno = EINVAL;
58 return -1;
59 }
60
61 // Extract any optional parameters required by the flags.
62 va_list args;
63 va_start(args, arg);
64 if ((flags & (CLONE_PARENT_SETTID|CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
65 parent_tid = va_arg(args, int*);
66 }
67 if ((flags & (CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
68 new_tls = va_arg(args, void*);
69 }
70 if ((flags & (CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
71 child_tid = va_arg(args, int*);
72 }
73 va_end(args);
74
75 // Align 'child_stack' to 16 bytes.
76 uintptr_t child_stack_addr = reinterpret_cast<uintptr_t>(child_stack);
77 child_stack_addr &= ~0xf;
78 child_stack = reinterpret_cast<void*>(child_stack_addr);
79
80 // Remember the parent pid and invalidate the cached value while we clone.
81 pthread_internal_t* self = __get_thread();
82 pid_t parent_pid = self->invalidate_cached_pid();
83
84 // Remmber the caller's tid so that it can be restored in the parent after clone.
85 pid_t caller_tid = self->tid;
86 // Invalidate the tid before the syscall. The value is lazily cached in gettid(),
87 // and it will be updated by fork() and pthread_create(). We don't do this if
88 // we are sharing address space with the child.
89 if (!(flags & (CLONE_VM|CLONE_VFORK))) {
90 self->tid = -1;
91 }
92
93 // Actually do the clone.
94 int clone_result;
95 if (fn != nullptr) {
96 clone_result = __bionic_clone(flags, child_stack, parent_tid, new_tls, child_tid, fn, arg);
97 } else {
98 #if defined(__x86_64__) // sys_clone's last two arguments are flipped on x86-64.
99 clone_result = syscall(__NR_clone, flags, child_stack, parent_tid, child_tid, new_tls);
100 #else
101 clone_result = syscall(__NR_clone, flags, child_stack, parent_tid, new_tls, child_tid);
102 #endif
103 }
104
105 if (clone_result != 0) {
106 // We're the parent, so put our known pid and tid back in place.
107 // We leave the child without a cached pid and tid, but:
108 // 1. pthread_create gives its children their own pthread_internal_t with the correct pid and tid.
109 // 2. fork uses CLONE_CHILD_SETTID to get the new pid/tid.
110 // 3. The tid is lazily fetched in gettid().
111 // If any other cases become important, we could use a double trampoline like __pthread_start.
112 self->set_cached_pid(parent_pid);
113 self->tid = caller_tid;
114 } else if (self->tid == -1) {
115 self->tid = syscall(__NR_gettid);
116 self->set_cached_pid(self->tid);
117 }
118
119 return clone_result;
120 }
121