pthread_create.cpp revision 03eebcb6e8762e668a0d3af6bb303cccb88c5b81
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_macros.h" 37#include "private/bionic_ssp.h" 38#include "private/bionic_tls.h" 39#include "private/libc_logging.h" 40#include "private/ErrnoRestorer.h" 41#include "private/ScopedPthreadMutexLocker.h" 42 43// Used by gdb to track thread creation. See libthread_db. 44#ifdef __i386__ 45extern "C" __attribute__((noinline)) __attribute__((fastcall)) void _thread_created_hook(pid_t) {} 46#else 47extern "C" __attribute__((noinline)) void _thread_created_hook(pid_t) {} 48#endif 49 50// x86 uses segment descriptors rather than a direct pointer to TLS. 51#if __i386__ 52#include <asm/ldt.h> 53extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*); 54#endif 55 56static pthread_mutex_t g_pthread_stack_creation_lock = PTHREAD_MUTEX_INITIALIZER; 57 58static pthread_mutex_t g_debugger_notification_lock = PTHREAD_MUTEX_INITIALIZER; 59 60extern "C" int __isthreaded; 61 62// This code is used both by each new pthread and the code that initializes the main thread. 63void __init_tls(pthread_internal_t* thread) { 64 // Zero-initialize all the slots after TLS_SLOT_SELF and TLS_SLOT_THREAD_ID. 65 for (size_t i = TLS_SLOT_ERRNO; i < BIONIC_TLS_SLOTS; ++i) { 66 thread->tls[i] = NULL; 67 } 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(&g_pthread_stack_creation_lock); 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_lock(&thread->startup_handshake_mutex); 149 pthread_mutex_destroy(&thread->startup_handshake_mutex); 150 151 __init_alternate_signal_stack(thread); 152 153 void* result = thread->start_routine(thread->start_routine_arg); 154 pthread_exit(result); 155 156 return 0; 157} 158 159// A dummy start routine for pthread_create failures where we've created a thread but aren't 160// going to run user code on it. We swap out the user's start routine for this and take advantage 161// of the regular thread teardown to free up resources. 162static void* __do_nothing(void*) { 163 return NULL; 164} 165 166int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 167 void* (*start_routine)(void*), void* arg) { 168 ErrnoRestorer errno_restorer; 169 170 // Inform the rest of the C library that at least one thread was created. 171 __isthreaded = 1; 172 173 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(calloc(sizeof(*thread), 1)); 174 if (thread == NULL) { 175 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: couldn't allocate thread"); 176 return EAGAIN; 177 } 178 179 if (attr == NULL) { 180 pthread_attr_init(&thread->attr); 181 } else { 182 thread->attr = *attr; 183 attr = NULL; // Prevent misuse below. 184 } 185 186 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 187 thread->attr.stack_size = BIONIC_ALIGN(thread->attr.stack_size, PAGE_SIZE); 188 thread->attr.guard_size = BIONIC_ALIGN(thread->attr.guard_size, PAGE_SIZE); 189 190 if (thread->attr.stack_base == NULL) { 191 // The caller didn't provide a stack, so allocate one. 192 thread->attr.stack_base = __create_thread_stack(thread); 193 if (thread->attr.stack_base == NULL) { 194 free(thread); 195 return EAGAIN; 196 } 197 } else { 198 // The caller did provide a stack, so remember we're not supposed to free it. 199 thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK; 200 } 201 202 // Make room for the TLS area. 203 // The child stack is the same address, just growing in the opposite direction. 204 // At offsets >= 0, we have the TLS slots. 205 // At offsets < 0, we have the child stack. 206 thread->tls = reinterpret_cast<void**>(reinterpret_cast<uint8_t*>(thread->attr.stack_base) + 207 thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*)); 208 void* child_stack = thread->tls; 209 __init_tls(thread); 210 211 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 212 // it from doing anything until after we notify the debugger about it 213 // 214 // This also provides the memory barrier we need to ensure that all 215 // memory accesses previously performed by this thread are visible to 216 // the new thread. 217 pthread_mutex_init(&thread->startup_handshake_mutex, NULL); 218 pthread_mutex_lock(&thread->startup_handshake_mutex); 219 220 thread->start_routine = start_routine; 221 thread->start_routine_arg = arg; 222 223 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 224 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 225 void* tls = thread->tls; 226#if defined(__i386__) 227 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 228 // a pointer to the TLS itself. 229 user_desc tls_descriptor; 230 __init_user_desc(&tls_descriptor, false, tls); 231 tls = &tls_descriptor; 232#endif 233 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 234 if (rc == -1) { 235 int clone_errno = errno; 236 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 237 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 238 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 239 pthread_mutex_unlock(&thread->startup_handshake_mutex); 240 if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) { 241 munmap(thread->attr.stack_base, thread->attr.stack_size); 242 } 243 free(thread); 244 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 245 return clone_errno; 246 } 247 248 int init_errno = __init_thread(thread, true); 249 if (init_errno != 0) { 250 // Mark the thread detached and replace its start_routine with a no-op. 251 // Letting the thread run is the easiest way to clean up its resources. 252 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 253 thread->start_routine = __do_nothing; 254 pthread_mutex_unlock(&thread->startup_handshake_mutex); 255 return init_errno; 256 } 257 258 // Notify any debuggers about the new thread. 259 { 260 ScopedPthreadMutexLocker debugger_locker(&g_debugger_notification_lock); 261 _thread_created_hook(thread->tid); 262 } 263 264 // Publish the pthread_t and unlock the mutex to let the new thread start running. 265 *thread_out = reinterpret_cast<pthread_t>(thread); 266 pthread_mutex_unlock(&thread->startup_handshake_mutex); 267 268 return 0; 269} 270