pthread_create.cpp revision b30aff405a220495941f1673b0a5e66c4fa8b84c
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/ErrnoRestorer.h" 40#include "private/ScopedPthreadMutexLocker.h" 41 42// Used by gdb to track thread creation. See libthread_db. 43#ifdef __i386__ 44extern "C" __attribute__((noinline)) __attribute__((fastcall)) void _thread_created_hook(pid_t) {} 45#else 46extern "C" __attribute__((noinline)) void _thread_created_hook(pid_t) {} 47#endif 48 49// x86 uses segment descriptors rather than a direct pointer to TLS. 50#if __i386__ 51#include <asm/ldt.h> 52extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*); 53#endif 54 55static pthread_mutex_t g_pthread_stack_creation_lock = PTHREAD_MUTEX_INITIALIZER; 56 57static pthread_mutex_t g_debugger_notification_lock = PTHREAD_MUTEX_INITIALIZER; 58 59extern "C" int __isthreaded; 60 61// This code is used both by each new pthread and the code that initializes the main thread. 62void __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 } 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(&g_pthread_stack_creation_lock); 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_lock(&thread->startup_handshake_mutex); 148 pthread_mutex_destroy(&thread->startup_handshake_mutex); 149 150 __init_alternate_signal_stack(thread); 151 152 void* result = thread->start_routine(thread->start_routine_arg); 153 pthread_exit(result); 154 155 return 0; 156} 157 158// 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. 161static void* __do_nothing(void*) { 162 return NULL; 163} 164 165int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 166 void* (*start_routine)(void*), void* arg) { 167 ErrnoRestorer errno_restorer; 168 169 // Inform the rest of the C library that at least one thread was created. 170 __isthreaded = 1; 171 172 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 } 177 178 if (attr == NULL) { 179 pthread_attr_init(&thread->attr); 180 } else { 181 thread->attr = *attr; 182 attr = NULL; // Prevent misuse below. 183 } 184 185 // 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); 188 189 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 } 200 201 // 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); 209 210 // 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); 218 219 thread->start_routine = start_routine; 220 thread->start_routine_arg = arg; 221 222 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 } 246 247 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 } 256 257 // Notify any debuggers about the new thread. 258 { 259 ScopedPthreadMutexLocker debugger_locker(&g_debugger_notification_lock); 260 _thread_created_hook(thread->tid); 261 } 262 263 // 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); 266 267 return 0; 268} 269