pthread_create.cpp revision f2cea021ab2c6d7d7feeb40cca098aa132605876
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 <pthread.h> 30 31#include <errno.h> 32#include <sys/mman.h> 33 34#include "pthread_internal.h" 35 36#include "private/bionic_ssp.h" 37#include "private/bionic_tls.h" 38#include "private/libc_logging.h" 39#include "private/thread_private.h" 40#include "private/ErrnoRestorer.h" 41#include "private/ScopedPthreadMutexLocker.h" 42 43extern "C" pid_t __bionic_clone(uint32_t flags, void* child_stack, int* parent_tid, void* tls, int* child_tid, int (*fn)(void*), void* arg); 44extern "C" int __set_tls(void*); 45 46// Used by gdb to track thread creation. See libthread_db. 47#ifdef __i386__ 48extern "C" __attribute__((noinline)) __attribute__((fastcall)) void _thread_created_hook(pid_t) {} 49#else 50extern "C" __attribute__((noinline)) void _thread_created_hook(pid_t) {} 51#endif 52 53static pthread_mutex_t gPthreadStackCreationLock = PTHREAD_MUTEX_INITIALIZER; 54 55static pthread_mutex_t gDebuggerNotificationLock = PTHREAD_MUTEX_INITIALIZER; 56 57extern "C" int __isthreaded; 58 59// This code is used both by each new pthread and the code that initializes the main thread. 60void __init_tls(pthread_internal_t* thread) { 61 // Zero-initialize all the slots after TLS_SLOT_SELF and TLS_SLOT_THREAD_ID. 62 for (size_t i = TLS_SLOT_ERRNO; i < BIONIC_TLS_SLOTS; ++i) { 63 thread->tls[i] = NULL; 64 } 65 66#if defined(__i386__) 67 __set_tls(thread->tls); 68#endif 69 70 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 71 thread->tls[TLS_SLOT_SELF] = thread->tls; 72 thread->tls[TLS_SLOT_THREAD_ID] = thread; 73 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 74 thread->tls[TLS_SLOT_STACK_GUARD] = (void*) __stack_chk_guard; 75} 76 77void __init_alternate_signal_stack(pthread_internal_t* thread) { 78 // Create and set an alternate signal stack. 79 stack_t ss; 80 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0); 81 if (ss.ss_sp != MAP_FAILED) { 82 ss.ss_size = SIGSTKSZ; 83 ss.ss_flags = 0; 84 sigaltstack(&ss, NULL); 85 thread->alternate_signal_stack = ss.ss_sp; 86 } 87} 88 89int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) { 90 int error = 0; 91 92 // Set the scheduling policy/priority of the thread. 93 if (thread->attr.sched_policy != SCHED_NORMAL) { 94 sched_param param; 95 param.sched_priority = thread->attr.sched_priority; 96 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 97#if __LP64__ 98 // For backwards compatibility reasons, we only report failures on 64-bit devices. 99 error = errno; 100#endif 101 __libc_format_log(ANDROID_LOG_WARN, "libc", 102 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 103 } 104 } 105 106 thread->cleanup_stack = NULL; 107 108 if (add_to_thread_list) { 109 _pthread_internal_add(thread); 110 } 111 112 return error; 113} 114 115static void* __create_thread_stack(pthread_internal_t* thread) { 116 ScopedPthreadMutexLocker lock(&gPthreadStackCreationLock); 117 118 // Create a new private anonymous map. 119 int prot = PROT_READ | PROT_WRITE; 120 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 121 void* stack = mmap(NULL, thread->attr.stack_size, prot, flags, -1, 0); 122 if (stack == MAP_FAILED) { 123 __libc_format_log(ANDROID_LOG_WARN, 124 "libc", 125 "pthread_create failed: couldn't allocate %zd-byte stack: %s", 126 thread->attr.stack_size, strerror(errno)); 127 return NULL; 128 } 129 130 // Set the guard region at the end of the stack to PROT_NONE. 131 if (mprotect(stack, thread->attr.guard_size, PROT_NONE) == -1) { 132 __libc_format_log(ANDROID_LOG_WARN, "libc", 133 "pthread_create failed: couldn't mprotect PROT_NONE %zd-byte stack guard region: %s", 134 thread->attr.guard_size, strerror(errno)); 135 munmap(stack, thread->attr.stack_size); 136 return NULL; 137 } 138 139 return stack; 140} 141 142static int __pthread_start(void* arg) { 143 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 144 145 // Wait for our creating thread to release us. This lets it have time to 146 // notify gdb about this thread before we start doing anything. 147 // This also provides the memory barrier needed to ensure that all memory 148 // accesses previously made by the creating thread are visible to us. 149 pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 150 pthread_mutex_lock(start_mutex); 151 pthread_mutex_destroy(start_mutex); 152 153 __init_tls(thread); 154 155 __init_alternate_signal_stack(thread); 156 157 void* result = thread->start_routine(thread->start_routine_arg); 158 pthread_exit(result); 159 160 return 0; 161} 162 163// A dummy start routine for pthread_create failures where we've created a thread but aren't 164// going to run user code on it. We swap out the user's start routine for this and take advantage 165// of the regular thread teardown to free up resources. 166static void* __do_nothing(void*) { 167 return NULL; 168} 169 170int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 171 void* (*start_routine)(void*), void* arg) { 172 ErrnoRestorer errno_restorer; 173 174 // Inform the rest of the C library that at least one thread was created. 175 __isthreaded = 1; 176 177 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(calloc(sizeof(*thread), 1)); 178 if (thread == NULL) { 179 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: couldn't allocate thread"); 180 return EAGAIN; 181 } 182 183 if (attr == NULL) { 184 pthread_attr_init(&thread->attr); 185 } else { 186 thread->attr = *attr; 187 attr = NULL; // Prevent misuse below. 188 } 189 190 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 191 thread->attr.stack_size = (thread->attr.stack_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 192 thread->attr.guard_size = (thread->attr.guard_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 193 194 if (thread->attr.stack_base == NULL) { 195 // The caller didn't provide a stack, so allocate one. 196 thread->attr.stack_base = __create_thread_stack(thread); 197 if (thread->attr.stack_base == NULL) { 198 free(thread); 199 return EAGAIN; 200 } 201 } else { 202 // The caller did provide a stack, so remember we're not supposed to free it. 203 thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK; 204 } 205 206 // Make room for the TLS area. 207 // The child stack is the same address, just growing in the opposite direction. 208 // At offsets >= 0, we have the TLS slots. 209 // At offsets < 0, we have the child stack. 210 thread->tls = (void**)((uint8_t*)(thread->attr.stack_base) + thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*)); 211 void* child_stack = thread->tls; 212 213 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 214 // it from doing anything until after we notify the debugger about it 215 // 216 // This also provides the memory barrier we need to ensure that all 217 // memory accesses previously performed by this thread are visible to 218 // the new thread. 219 pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 220 pthread_mutex_init(start_mutex, NULL); 221 pthread_mutex_lock(start_mutex); 222 223 thread->tls[TLS_SLOT_THREAD_ID] = thread; 224 225 thread->start_routine = start_routine; 226 thread->start_routine_arg = arg; 227 228 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 229 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 230#if defined(__i386__) 231 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 232 // a pointer to the TLS itself. Rather than try to deal with that here, we just let x86 set 233 // the TLS manually in __init_tls, like all architectures used to. 234 flags &= ~CLONE_SETTLS; 235#endif 236 int rc = __bionic_clone(flags, child_stack, &(thread->tid), thread->tls, &(thread->tid), __pthread_start, thread); 237 if (rc == -1) { 238 int clone_errno = errno; 239 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 240 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 241 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 242 pthread_mutex_unlock(start_mutex); 243 if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) { 244 munmap(thread->attr.stack_base, thread->attr.stack_size); 245 } 246 free(thread); 247 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 248 return clone_errno; 249 } 250 251 int init_errno = __init_thread(thread, true); 252 if (init_errno != 0) { 253 // Mark the thread detached and replace its start_routine with a no-op. 254 // Letting the thread run is the easiest way to clean up its resources. 255 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 256 thread->start_routine = __do_nothing; 257 pthread_mutex_unlock(start_mutex); 258 return init_errno; 259 } 260 261 // Notify any debuggers about the new thread. 262 { 263 ScopedPthreadMutexLocker debugger_locker(&gDebuggerNotificationLock); 264 _thread_created_hook(thread->tid); 265 } 266 267 // Publish the pthread_t and unlock the mutex to let the new thread start running. 268 *thread_out = reinterpret_cast<pthread_t>(thread); 269 pthread_mutex_unlock(start_mutex); 270 271 return 0; 272} 273