pthread_create.cpp revision a3125fd1396a09a7fc4872dc4653f342150a3deb
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 <string.h> 33#include <sys/mman.h> 34#include <unistd.h> 35 36#include "pthread_internal.h" 37 38#include "private/bionic_macros.h" 39#include "private/bionic_prctl.h" 40#include "private/bionic_ssp.h" 41#include "private/bionic_tls.h" 42#include "private/libc_logging.h" 43#include "private/ErrnoRestorer.h" 44#include "private/ScopedPthreadMutexLocker.h" 45 46// x86 uses segment descriptors rather than a direct pointer to TLS. 47#if __i386__ 48#include <asm/ldt.h> 49extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*); 50#endif 51 52extern "C" int __isthreaded; 53 54// This code is used both by each new pthread and the code that initializes the main thread. 55void __init_tls(pthread_internal_t* thread) { 56 if (thread->mmap_size == 0) { 57 // If the TLS area was not allocated by mmap(), it may not have been cleared to zero. 58 // So assume the worst and zero the TLS area. 59 memset(thread->tls, 0, sizeof(thread->tls)); 60 memset(thread->key_data, 0, sizeof(thread->key_data)); 61 } 62 63 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 64 thread->tls[TLS_SLOT_SELF] = thread->tls; 65 thread->tls[TLS_SLOT_THREAD_ID] = thread; 66 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 67 thread->tls[TLS_SLOT_STACK_GUARD] = reinterpret_cast<void*>(__stack_chk_guard); 68} 69 70void __init_alternate_signal_stack(pthread_internal_t* thread) { 71 // Create and set an alternate signal stack. 72 stack_t ss; 73 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 74 if (ss.ss_sp != MAP_FAILED) { 75 ss.ss_size = SIGSTKSZ; 76 ss.ss_flags = 0; 77 sigaltstack(&ss, NULL); 78 thread->alternate_signal_stack = ss.ss_sp; 79 80 // We can only use const static allocated string for mapped region name, as Android kernel 81 // uses the string pointer directly when dumping /proc/pid/maps. 82 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); 83 } 84} 85 86int __init_thread(pthread_internal_t* thread) { 87 int error = 0; 88 89 if (__predict_true((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) == 0)) { 90 atomic_init(&thread->join_state, THREAD_NOT_JOINED); 91 } else { 92 atomic_init(&thread->join_state, THREAD_DETACHED); 93 } 94 95 // Set the scheduling policy/priority of the thread. 96 if (thread->attr.sched_policy != SCHED_NORMAL) { 97 sched_param param; 98 param.sched_priority = thread->attr.sched_priority; 99 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 100#if __LP64__ 101 // For backwards compatibility reasons, we only report failures on 64-bit devices. 102 error = errno; 103#endif 104 __libc_format_log(ANDROID_LOG_WARN, "libc", 105 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 106 } 107 } 108 109 thread->cleanup_stack = NULL; 110 111 return error; 112} 113 114static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 115 // Create a new private anonymous map. 116 int prot = PROT_READ | PROT_WRITE; 117 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 118 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 119 if (space == MAP_FAILED) { 120 __libc_format_log(ANDROID_LOG_WARN, 121 "libc", 122 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 123 mmap_size, strerror(errno)); 124 return NULL; 125 } 126 127 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 128 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 129 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 130 __libc_format_log(ANDROID_LOG_WARN, "libc", 131 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 132 stack_guard_size, strerror(errno)); 133 munmap(space, mmap_size); 134 return NULL; 135 } 136 137 return space; 138} 139 140static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 141 size_t mmap_size; 142 uint8_t* stack_top; 143 144 if (attr->stack_base == NULL) { 145 // The caller didn't provide a stack, so allocate one. 146 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 147 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 148 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 149 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 150 if (attr->stack_base == NULL) { 151 return EAGAIN; 152 } 153 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 154 } else { 155 // Remember the mmap size is zero and we don't need to free it. 156 mmap_size = 0; 157 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 158 } 159 160 // Mapped space(or user allocated stack) is used for: 161 // pthread_internal_t 162 // thread stack (including guard page) 163 164 // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary. 165 stack_top = reinterpret_cast<uint8_t*>( 166 (reinterpret_cast<uintptr_t>(stack_top) - sizeof(pthread_internal_t)) & ~0xf); 167 168 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 169 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base); 170 171 thread->mmap_size = mmap_size; 172 thread->attr = *attr; 173 __init_tls(thread); 174 175 *threadp = thread; 176 *child_stack = stack_top; 177 return 0; 178} 179 180static int __pthread_start(void* arg) { 181 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 182 183 // Wait for our creating thread to release us. This lets it have time to 184 // notify gdb about this thread before we start doing anything. 185 // This also provides the memory barrier needed to ensure that all memory 186 // accesses previously made by the creating thread are visible to us. 187 pthread_mutex_lock(&thread->startup_handshake_mutex); 188 pthread_mutex_destroy(&thread->startup_handshake_mutex); 189 190 __init_alternate_signal_stack(thread); 191 192 void* result = thread->start_routine(thread->start_routine_arg); 193 pthread_exit(result); 194 195 return 0; 196} 197 198// A dummy start routine for pthread_create failures where we've created a thread but aren't 199// going to run user code on it. We swap out the user's start routine for this and take advantage 200// of the regular thread teardown to free up resources. 201static void* __do_nothing(void*) { 202 return NULL; 203} 204 205int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 206 void* (*start_routine)(void*), void* arg) { 207 ErrnoRestorer errno_restorer; 208 209 // Inform the rest of the C library that at least one thread was created. 210 __isthreaded = 1; 211 212 pthread_attr_t thread_attr; 213 if (attr == NULL) { 214 pthread_attr_init(&thread_attr); 215 } else { 216 thread_attr = *attr; 217 attr = NULL; // Prevent misuse below. 218 } 219 220 pthread_internal_t* thread = NULL; 221 void* child_stack = NULL; 222 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 223 if (result != 0) { 224 return result; 225 } 226 227 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 228 // it from doing anything until after we notify the debugger about it 229 // 230 // This also provides the memory barrier we need to ensure that all 231 // memory accesses previously performed by this thread are visible to 232 // the new thread. 233 pthread_mutex_init(&thread->startup_handshake_mutex, NULL); 234 pthread_mutex_lock(&thread->startup_handshake_mutex); 235 236 thread->start_routine = start_routine; 237 thread->start_routine_arg = arg; 238 239 thread->set_cached_pid(getpid()); 240 241 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 242 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 243 void* tls = reinterpret_cast<void*>(thread->tls); 244#if defined(__i386__) 245 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 246 // a pointer to the TLS itself. 247 user_desc tls_descriptor; 248 __init_user_desc(&tls_descriptor, false, tls); 249 tls = &tls_descriptor; 250#endif 251 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 252 if (rc == -1) { 253 int clone_errno = errno; 254 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 255 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 256 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 257 pthread_mutex_unlock(&thread->startup_handshake_mutex); 258 if (thread->mmap_size != 0) { 259 munmap(thread->attr.stack_base, thread->mmap_size); 260 } 261 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 262 return clone_errno; 263 } 264 265 int init_errno = __init_thread(thread); 266 if (init_errno != 0) { 267 // Mark the thread detached and replace its start_routine with a no-op. 268 // Letting the thread run is the easiest way to clean up its resources. 269 atomic_store(&thread->join_state, THREAD_DETACHED); 270 __pthread_internal_add(thread); 271 thread->start_routine = __do_nothing; 272 pthread_mutex_unlock(&thread->startup_handshake_mutex); 273 return init_errno; 274 } 275 276 // Publish the pthread_t and unlock the mutex to let the new thread start running. 277 *thread_out = __pthread_internal_add(thread); 278 pthread_mutex_unlock(&thread->startup_handshake_mutex); 279 280 return 0; 281} 282