pthread_create.cpp revision af8aebebb52d73ea38c604525a6a5857618861cf
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 57// This code is used both by each new pthread and the code that initializes the main thread. 58void __init_tls(pthread_internal_t* thread) { 59 // Zero-initialize all the slots after TLS_SLOT_SELF and TLS_SLOT_THREAD_ID. 60 for (size_t i = TLS_SLOT_ERRNO; i < BIONIC_TLS_SLOTS; ++i) { 61 thread->tls[i] = NULL; 62 } 63 64#if defined(__i386__) 65 __set_tls(thread->tls); 66#endif 67 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} 74 75void __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} 86 87int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) { 88 int error = 0; 89 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 } 103 104 thread->cleanup_stack = NULL; 105 106 if (add_to_thread_list) { 107 _pthread_internal_add(thread); 108 } 109 110 return error; 111} 112 113static void* __create_thread_stack(pthread_internal_t* thread) { 114 ScopedPthreadMutexLocker lock(&gPthreadStackCreationLock); 115 116 // 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 } 127 128 // 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 } 136 137 return stack; 138} 139 140static int __pthread_start(void* arg) { 141 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 142 143 // 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_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 148 pthread_mutex_lock(start_mutex); 149 pthread_mutex_destroy(start_mutex); 150 151 __init_tls(thread); 152 153 __init_alternate_signal_stack(thread); 154 155 void* result = thread->start_routine(thread->start_routine_arg); 156 pthread_exit(result); 157 158 return 0; 159} 160 161// A dummy start routine for pthread_create failures where we've created a thread but aren't 162// going to run user code on it. We swap out the user's start routine for this and take advantage 163// of the regular thread teardown to free up resources. 164static void* __do_nothing(void*) { 165 return NULL; 166} 167 168int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 169 void* (*start_routine)(void*), void* arg) { 170 ErrnoRestorer errno_restorer; 171 172 // Inform the rest of the C library that at least one thread 173 // was created. This will enforce certain functions to acquire/release 174 // locks (e.g. atexit()) to protect shared global structures. 175 // This works because pthread_create() is not called by the C library 176 // initialization routine that sets up the main thread's data structures. 177 __isthreaded = 1; 178 179 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(calloc(sizeof(*thread), 1)); 180 if (thread == NULL) { 181 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: couldn't allocate thread"); 182 return EAGAIN; 183 } 184 185 if (attr == NULL) { 186 pthread_attr_init(&thread->attr); 187 } else { 188 thread->attr = *attr; 189 attr = NULL; // Prevent misuse below. 190 } 191 192 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 193 thread->attr.stack_size = (thread->attr.stack_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 194 thread->attr.guard_size = (thread->attr.guard_size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1); 195 196 if (thread->attr.stack_base == NULL) { 197 // The caller didn't provide a stack, so allocate one. 198 thread->attr.stack_base = __create_thread_stack(thread); 199 if (thread->attr.stack_base == NULL) { 200 free(thread); 201 return EAGAIN; 202 } 203 } else { 204 // The caller did provide a stack, so remember we're not supposed to free it. 205 thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK; 206 } 207 208 // Make room for the TLS area. 209 // The child stack is the same address, just growing in the opposite direction. 210 // At offsets >= 0, we have the TLS slots. 211 // At offsets < 0, we have the child stack. 212 thread->tls = (void**)((uint8_t*)(thread->attr.stack_base) + thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*)); 213 void* child_stack = thread->tls; 214 215 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 216 // it from doing anything until after we notify the debugger about it 217 // 218 // This also provides the memory barrier we need to ensure that all 219 // memory accesses previously performed by this thread are visible to 220 // the new thread. 221 pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; 222 pthread_mutex_init(start_mutex, NULL); 223 pthread_mutex_lock(start_mutex); 224 225 thread->tls[TLS_SLOT_THREAD_ID] = thread; 226 227 thread->start_routine = start_routine; 228 thread->start_routine_arg = arg; 229 230 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 231 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 232#if defined(__i386__) 233 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 234 // a pointer to the TLS itself. Rather than try to deal with that here, we just let x86 set 235 // the TLS manually in __init_tls, like all architectures used to. 236 flags &= ~CLONE_SETTLS; 237#endif 238 int rc = __bionic_clone(flags, child_stack, &(thread->tid), thread->tls, &(thread->tid), __pthread_start, thread); 239 if (rc == -1) { 240 int clone_errno = errno; 241 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 242 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 243 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 244 pthread_mutex_unlock(start_mutex); 245 if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) { 246 munmap(thread->attr.stack_base, thread->attr.stack_size); 247 } 248 free(thread); 249 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 250 return clone_errno; 251 } 252 253 int init_errno = __init_thread(thread, true); 254 if (init_errno != 0) { 255 // Mark the thread detached and replace its start_routine with a no-op. 256 // Letting the thread run is the easiest way to clean up its resources. 257 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 258 thread->start_routine = __do_nothing; 259 pthread_mutex_unlock(start_mutex); 260 return init_errno; 261 } 262 263 // Notify any debuggers about the new thread. 264 { 265 ScopedPthreadMutexLocker debugger_locker(&gDebuggerNotificationLock); 266 _thread_created_hook(thread->tid); 267 } 268 269 // Publish the pthread_t and unlock the mutex to let the new thread start running. 270 *thread_out = reinterpret_cast<pthread_t>(thread); 271 pthread_mutex_unlock(start_mutex); 272 273 return 0; 274} 275