pthread_create.cpp revision 80906141f79be8be63fc915bfab467029b442ca1
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#ifdef __i386__ 47#define ATTRIBUTES __attribute__((noinline)) __attribute__((fastcall)) 48#else 49#define ATTRIBUTES __attribute__((noinline)) 50#endif 51 52extern "C" void ATTRIBUTES _thread_created_hook(pid_t thread_id); 53 54static pthread_mutex_t gPthreadStackCreationLock = PTHREAD_MUTEX_INITIALIZER; 55 56static pthread_mutex_t gDebuggerNotificationLock = PTHREAD_MUTEX_INITIALIZER; 57 58// This code is used both by each new pthread and the code that initializes the main thread. 59void __init_tls(pthread_internal_t* thread) { 60 // Zero-initialize all the slots after TLS_SLOT_SELF and TLS_SLOT_THREAD_ID. 61 for (size_t i = TLS_SLOT_ERRNO; i < BIONIC_TLS_SLOTS; ++i) { 62 thread->tls[i] = NULL; 63 } 64 65#if defined(__i386__) 66 __set_tls(thread->tls); 67#endif 68 69 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 70 thread->tls[TLS_SLOT_SELF] = thread->tls; 71 thread->tls[TLS_SLOT_THREAD_ID] = thread; 72 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 73 thread->tls[TLS_SLOT_STACK_GUARD] = (void*) __stack_chk_guard; 74} 75 76void __init_alternate_signal_stack(pthread_internal_t* thread) { 77 // Create and set an alternate signal stack. 78 stack_t ss; 79 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0); 80 if (ss.ss_sp != MAP_FAILED) { 81 ss.ss_size = SIGSTKSZ; 82 ss.ss_flags = 0; 83 sigaltstack(&ss, NULL); 84 thread->alternate_signal_stack = ss.ss_sp; 85 } 86} 87 88int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) { 89 int error = 0; 90 91 // Set the scheduling policy/priority of the thread. 92 if (thread->attr.sched_policy != SCHED_NORMAL) { 93 sched_param param; 94 param.sched_priority = thread->attr.sched_priority; 95 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 96#if __LP64__ 97 // For backwards compatibility reasons, we only report failures on 64-bit devices. 98 error = errno; 99#endif 100 __libc_format_log(ANDROID_LOG_WARN, "libc", 101 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 102 } 103 } 104 105 thread->cleanup_stack = NULL; 106 107 if (add_to_thread_list) { 108 _pthread_internal_add(thread); 109 } 110 111 return error; 112} 113 114static void* __create_thread_stack(pthread_internal_t* thread) { 115 ScopedPthreadMutexLocker lock(&gPthreadStackCreationLock); 116 117 // Create a new private anonymous map. 118 int prot = PROT_READ | PROT_WRITE; 119 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 120 void* stack = mmap(NULL, thread->attr.stack_size, prot, flags, -1, 0); 121 if (stack == MAP_FAILED) { 122 __libc_format_log(ANDROID_LOG_WARN, 123 "libc", 124 "pthread_create failed: couldn't allocate %zd-byte stack: %s", 125 thread->attr.stack_size, strerror(errno)); 126 return NULL; 127 } 128 129 // Set the guard region at the end of the stack to PROT_NONE. 130 if (mprotect(stack, thread->attr.guard_size, PROT_NONE) == -1) { 131 __libc_format_log(ANDROID_LOG_WARN, "libc", 132 "pthread_create failed: couldn't mprotect PROT_NONE %zd-byte stack guard region: %s", 133 thread->attr.guard_size, strerror(errno)); 134 munmap(stack, thread->attr.stack_size); 135 return NULL; 136 } 137 138 return stack; 139} 140 141static int __pthread_start(void* arg) { 142 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 143 144 // Wait for our creating thread to release us. This lets it have time to 145 // notify gdb about this thread before we start doing anything. 146 // This also provides the memory barrier needed to ensure that all memory 147 // accesses previously made by the creating thread are visible to us. 148 pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 149 pthread_mutex_lock(start_mutex); 150 pthread_mutex_destroy(start_mutex); 151 152 __init_tls(thread); 153 154 __init_alternate_signal_stack(thread); 155 156 void* result = thread->start_routine(thread->start_routine_arg); 157 pthread_exit(result); 158 159 return 0; 160} 161 162// A dummy start routine for pthread_create failures where we've created a thread but aren't 163// going to run user code on it. We swap out the user's start routine for this and take advantage 164// of the regular thread teardown to free up resources. 165static void* __do_nothing(void*) { 166 return NULL; 167} 168 169int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 170 void* (*start_routine)(void*), void* arg) { 171 ErrnoRestorer errno_restorer; 172 173 // Inform the rest of the C library that at least one thread 174 // was created. This will enforce certain functions to acquire/release 175 // locks (e.g. atexit()) to protect shared global structures. 176 // This works because pthread_create() is not called by the C library 177 // initialization routine that sets up the main thread's data structures. 178 __isthreaded = 1; 179 180 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(calloc(sizeof(*thread), 1)); 181 if (thread == NULL) { 182 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: couldn't allocate thread"); 183 return EAGAIN; 184 } 185 186 if (attr == NULL) { 187 pthread_attr_init(&thread->attr); 188 } else { 189 thread->attr = *attr; 190 attr = NULL; // Prevent misuse below. 191 } 192 193 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 194 thread->attr.stack_size = (thread->attr.stack_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 195 thread->attr.guard_size = (thread->attr.guard_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 196 197 if (thread->attr.stack_base == NULL) { 198 // The caller didn't provide a stack, so allocate one. 199 thread->attr.stack_base = __create_thread_stack(thread); 200 if (thread->attr.stack_base == NULL) { 201 free(thread); 202 return EAGAIN; 203 } 204 } else { 205 // The caller did provide a stack, so remember we're not supposed to free it. 206 thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK; 207 } 208 209 // Make room for the TLS area. 210 // The child stack is the same address, just growing in the opposite direction. 211 // At offsets >= 0, we have the TLS slots. 212 // At offsets < 0, we have the child stack. 213 thread->tls = (void**)((uint8_t*)(thread->attr.stack_base) + thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*)); 214 void* child_stack = thread->tls; 215 216 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 217 // it from doing anything until after we notify the debugger about it 218 // 219 // This also provides the memory barrier we need to ensure that all 220 // memory accesses previously performed by this thread are visible to 221 // the new thread. 222 pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 223 pthread_mutex_init(start_mutex, NULL); 224 pthread_mutex_lock(start_mutex); 225 226 thread->tls[TLS_SLOT_THREAD_ID] = thread; 227 228 thread->start_routine = start_routine; 229 thread->start_routine_arg = arg; 230 231 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 232 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 233#if defined(__i386__) 234 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 235 // a pointer to the TLS itself. Rather than try to deal with that here, we just let x86 set 236 // the TLS manually in __init_tls, like all architectures used to. 237 flags &= ~CLONE_SETTLS; 238#endif 239 int rc = __bionic_clone(flags, child_stack, &(thread->tid), thread->tls, &(thread->tid), __pthread_start, thread); 240 if (rc == -1) { 241 int clone_errno = errno; 242 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 243 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 244 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 245 pthread_mutex_unlock(start_mutex); 246 if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) { 247 munmap(thread->attr.stack_base, thread->attr.stack_size); 248 } 249 free(thread); 250 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 251 return clone_errno; 252 } 253 254 int init_errno = __init_thread(thread, true); 255 if (init_errno != 0) { 256 // Mark the thread detached and replace its start_routine with a no-op. 257 // Letting the thread run is the easiest way to clean up its resources. 258 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 259 thread->start_routine = __do_nothing; 260 pthread_mutex_unlock(start_mutex); 261 return init_errno; 262 } 263 264 // Notify any debuggers about the new thread. 265 { 266 ScopedPthreadMutexLocker debugger_locker(&gDebuggerNotificationLock); 267 _thread_created_hook(thread->tid); 268 } 269 270 // Publish the pthread_t and unlock the mutex to let the new thread start running. 271 *thread_out = reinterpret_cast<pthread_t>(thread); 272 pthread_mutex_unlock(start_mutex); 273 274 return 0; 275} 276