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 */
29 #include <pthread.h>
31 #include <errno.h>
32 #include <sys/mman.h>
34 #include "pthread_internal.h"
36 #include "private/bionic_ssp.h"
37 #include "private/bionic_tls.h"
38 #include "private/libc_logging.h"
39 #include "private/ErrnoRestorer.h"
40 #include "private/ScopedPthreadMutexLocker.h"
42 // Used by gdb to track thread creation. See libthread_db.
43 #ifdef __i386__
44 extern "C" __attribute__((noinline)) __attribute__((fastcall)) void _thread_created_hook(pid_t) {}
45 #else
46 extern "C" __attribute__((noinline)) void _thread_created_hook(pid_t) {}
47 #endif
49 // x86 uses segment descriptors rather than a direct pointer to TLS.
50 #if __i386__
51 #include <asm/ldt.h>
52 extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*);
53 #endif
55 static pthread_mutex_t g_pthread_stack_creation_lock = PTHREAD_MUTEX_INITIALIZER;
57 static pthread_mutex_t g_debugger_notification_lock = PTHREAD_MUTEX_INITIALIZER;
59 extern "C" int __isthreaded;
61 // This code is used both by each new pthread and the code that initializes the main thread.
62 void __init_tls(pthread_internal_t* thread) {
63 // Zero-initialize all the slots after TLS_SLOT_SELF and TLS_SLOT_THREAD_ID.
64 for (size_t i = TLS_SLOT_ERRNO; i < BIONIC_TLS_SLOTS; ++i) {
65 thread->tls[i] = NULL;
66 }
68 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0.
69 thread->tls[TLS_SLOT_SELF] = thread->tls;
70 thread->tls[TLS_SLOT_THREAD_ID] = thread;
71 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global.
72 thread->tls[TLS_SLOT_STACK_GUARD] = (void*) __stack_chk_guard;
73 }
75 void __init_alternate_signal_stack(pthread_internal_t* thread) {
76 // Create and set an alternate signal stack.
77 stack_t ss;
78 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
79 if (ss.ss_sp != MAP_FAILED) {
80 ss.ss_size = SIGSTKSZ;
81 ss.ss_flags = 0;
82 sigaltstack(&ss, NULL);
83 thread->alternate_signal_stack = ss.ss_sp;
84 }
85 }
87 int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) {
88 int error = 0;
90 // Set the scheduling policy/priority of the thread.
91 if (thread->attr.sched_policy != SCHED_NORMAL) {
92 sched_param param;
93 param.sched_priority = thread->attr.sched_priority;
94 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) {
95 #if __LP64__
96 // For backwards compatibility reasons, we only report failures on 64-bit devices.
97 error = errno;
98 #endif
99 __libc_format_log(ANDROID_LOG_WARN, "libc",
100 "pthread_create sched_setscheduler call failed: %s", strerror(errno));
101 }
102 }
104 thread->cleanup_stack = NULL;
106 if (add_to_thread_list) {
107 _pthread_internal_add(thread);
108 }
110 return error;
111 }
113 static void* __create_thread_stack(pthread_internal_t* thread) {
114 ScopedPthreadMutexLocker lock(&g_pthread_stack_creation_lock);
116 // Create a new private anonymous map.
117 int prot = PROT_READ | PROT_WRITE;
118 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
119 void* stack = mmap(NULL, thread->attr.stack_size, prot, flags, -1, 0);
120 if (stack == MAP_FAILED) {
121 __libc_format_log(ANDROID_LOG_WARN,
122 "libc",
123 "pthread_create failed: couldn't allocate %zd-byte stack: %s",
124 thread->attr.stack_size, strerror(errno));
125 return NULL;
126 }
128 // Set the guard region at the end of the stack to PROT_NONE.
129 if (mprotect(stack, thread->attr.guard_size, PROT_NONE) == -1) {
130 __libc_format_log(ANDROID_LOG_WARN, "libc",
131 "pthread_create failed: couldn't mprotect PROT_NONE %zd-byte stack guard region: %s",
132 thread->attr.guard_size, strerror(errno));
133 munmap(stack, thread->attr.stack_size);
134 return NULL;
135 }
137 return stack;
138 }
140 static int __pthread_start(void* arg) {
141 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg);
143 // Wait for our creating thread to release us. This lets it have time to
144 // notify gdb about this thread before we start doing anything.
145 // This also provides the memory barrier needed to ensure that all memory
146 // accesses previously made by the creating thread are visible to us.
147 pthread_mutex_lock(&thread->startup_handshake_mutex);
148 pthread_mutex_destroy(&thread->startup_handshake_mutex);
150 __init_alternate_signal_stack(thread);
152 void* result = thread->start_routine(thread->start_routine_arg);
153 pthread_exit(result);
155 return 0;
156 }
158 // A dummy start routine for pthread_create failures where we've created a thread but aren't
159 // going to run user code on it. We swap out the user's start routine for this and take advantage
160 // of the regular thread teardown to free up resources.
161 static void* __do_nothing(void*) {
162 return NULL;
163 }
165 int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
166 void* (*start_routine)(void*), void* arg) {
167 ErrnoRestorer errno_restorer;
169 // Inform the rest of the C library that at least one thread was created.
170 __isthreaded = 1;
172 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(calloc(sizeof(*thread), 1));
173 if (thread == NULL) {
174 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: couldn't allocate thread");
175 return EAGAIN;
176 }
178 if (attr == NULL) {
179 pthread_attr_init(&thread->attr);
180 } else {
181 thread->attr = *attr;
182 attr = NULL; // Prevent misuse below.
183 }
185 // Make sure the stack size and guard size are multiples of PAGE_SIZE.
186 thread->attr.stack_size = (thread->attr.stack_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);
187 thread->attr.guard_size = (thread->attr.guard_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);
189 if (thread->attr.stack_base == NULL) {
190 // The caller didn't provide a stack, so allocate one.
191 thread->attr.stack_base = __create_thread_stack(thread);
192 if (thread->attr.stack_base == NULL) {
193 free(thread);
194 return EAGAIN;
195 }
196 } else {
197 // The caller did provide a stack, so remember we're not supposed to free it.
198 thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK;
199 }
201 // Make room for the TLS area.
202 // The child stack is the same address, just growing in the opposite direction.
203 // At offsets >= 0, we have the TLS slots.
204 // At offsets < 0, we have the child stack.
205 thread->tls = reinterpret_cast<void**>(reinterpret_cast<uint8_t*>(thread->attr.stack_base) +
206 thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*));
207 void* child_stack = thread->tls;
208 __init_tls(thread);
210 // Create a mutex for the thread in TLS to wait on once it starts so we can keep
211 // it from doing anything until after we notify the debugger about it
212 //
213 // This also provides the memory barrier we need to ensure that all
214 // memory accesses previously performed by this thread are visible to
215 // the new thread.
216 pthread_mutex_init(&thread->startup_handshake_mutex, NULL);
217 pthread_mutex_lock(&thread->startup_handshake_mutex);
219 thread->start_routine = start_routine;
220 thread->start_routine_arg = arg;
222 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
223 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID;
224 void* tls = thread->tls;
225 #if defined(__i386__)
226 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than
227 // a pointer to the TLS itself.
228 user_desc tls_descriptor;
229 __init_user_desc(&tls_descriptor, false, tls);
230 tls = &tls_descriptor;
231 #endif
232 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid));
233 if (rc == -1) {
234 int clone_errno = errno;
235 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to
236 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a
237 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker.
238 pthread_mutex_unlock(&thread->startup_handshake_mutex);
239 if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) {
240 munmap(thread->attr.stack_base, thread->attr.stack_size);
241 }
242 free(thread);
243 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno));
244 return clone_errno;
245 }
247 int init_errno = __init_thread(thread, true);
248 if (init_errno != 0) {
249 // Mark the thread detached and replace its start_routine with a no-op.
250 // Letting the thread run is the easiest way to clean up its resources.
251 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED;
252 thread->start_routine = __do_nothing;
253 pthread_mutex_unlock(&thread->startup_handshake_mutex);
254 return init_errno;
255 }
257 // Notify any debuggers about the new thread.
258 {
259 ScopedPthreadMutexLocker debugger_locker(&g_debugger_notification_lock);
260 _thread_created_hook(thread->tid);
261 }
263 // Publish the pthread_t and unlock the mutex to let the new thread start running.
264 *thread_out = reinterpret_cast<pthread_t>(thread);
265 pthread_mutex_unlock(&thread->startup_handshake_mutex);
267 return 0;
268 }