pthread_create.cpp revision d26e780df66b9add4cf7e7ebb2f6c6749d1c5050
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 void* stack_base = mmap(NULL, SIGNAL_STACK_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 73 if (stack_base != MAP_FAILED) { 74 75 // Create a guard page to catch stack overflows in signal handlers. 76 if (mprotect(stack_base, PAGE_SIZE, PROT_NONE) == -1) { 77 munmap(stack_base, SIGNAL_STACK_SIZE); 78 return; 79 } 80 stack_t ss; 81 ss.ss_sp = reinterpret_cast<uint8_t*>(stack_base) + PAGE_SIZE; 82 ss.ss_size = SIGNAL_STACK_SIZE - PAGE_SIZE; 83 ss.ss_flags = 0; 84 sigaltstack(&ss, NULL); 85 thread->alternate_signal_stack = stack_base; 86 87 // We can only use const static allocated string for mapped region name, as Android kernel 88 // uses the string pointer directly when dumping /proc/pid/maps. 89 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); 90 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, stack_base, PAGE_SIZE, "thread signal stack guard page"); 91 } 92} 93 94int __init_thread(pthread_internal_t* thread) { 95 int error = 0; 96 97 if (__predict_true((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) == 0)) { 98 atomic_init(&thread->join_state, THREAD_NOT_JOINED); 99 } else { 100 atomic_init(&thread->join_state, THREAD_DETACHED); 101 } 102 103 // Set the scheduling policy/priority of the thread. 104 if (thread->attr.sched_policy != SCHED_NORMAL) { 105 sched_param param; 106 param.sched_priority = thread->attr.sched_priority; 107 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 108#if __LP64__ 109 // For backwards compatibility reasons, we only report failures on 64-bit devices. 110 error = errno; 111#endif 112 __libc_format_log(ANDROID_LOG_WARN, "libc", 113 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 114 } 115 } 116 117 thread->cleanup_stack = NULL; 118 119 return error; 120} 121 122static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 123 // Create a new private anonymous map. 124 int prot = PROT_READ | PROT_WRITE; 125 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 126 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 127 if (space == MAP_FAILED) { 128 __libc_format_log(ANDROID_LOG_WARN, 129 "libc", 130 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 131 mmap_size, strerror(errno)); 132 return NULL; 133 } 134 135 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 136 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 137 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 138 __libc_format_log(ANDROID_LOG_WARN, "libc", 139 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 140 stack_guard_size, strerror(errno)); 141 munmap(space, mmap_size); 142 return NULL; 143 } 144 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, space, stack_guard_size, "thread stack guard page"); 145 146 return space; 147} 148 149static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 150 size_t mmap_size; 151 uint8_t* stack_top; 152 153 if (attr->stack_base == NULL) { 154 // The caller didn't provide a stack, so allocate one. 155 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 156 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 157 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 158 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 159 if (attr->stack_base == NULL) { 160 return EAGAIN; 161 } 162 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 163 } else { 164 // Remember the mmap size is zero and we don't need to free it. 165 mmap_size = 0; 166 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 167 } 168 169 // Mapped space(or user allocated stack) is used for: 170 // pthread_internal_t 171 // thread stack (including guard page) 172 173 // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary. 174 stack_top = reinterpret_cast<uint8_t*>( 175 (reinterpret_cast<uintptr_t>(stack_top) - sizeof(pthread_internal_t)) & ~0xf); 176 177 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 178 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base); 179 180 thread->mmap_size = mmap_size; 181 thread->attr = *attr; 182 __init_tls(thread); 183 184 *threadp = thread; 185 *child_stack = stack_top; 186 return 0; 187} 188 189static int __pthread_start(void* arg) { 190 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 191 192 // Wait for our creating thread to release us. This lets it have time to 193 // notify gdb about this thread before we start doing anything. 194 // This also provides the memory barrier needed to ensure that all memory 195 // accesses previously made by the creating thread are visible to us. 196 thread->startup_handshake_lock.lock(); 197 198 __init_alternate_signal_stack(thread); 199 200 void* result = thread->start_routine(thread->start_routine_arg); 201 pthread_exit(result); 202 203 return 0; 204} 205 206// A dummy start routine for pthread_create failures where we've created a thread but aren't 207// going to run user code on it. We swap out the user's start routine for this and take advantage 208// of the regular thread teardown to free up resources. 209static void* __do_nothing(void*) { 210 return NULL; 211} 212 213int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 214 void* (*start_routine)(void*), void* arg) { 215 ErrnoRestorer errno_restorer; 216 217 // Inform the rest of the C library that at least one thread was created. 218 __isthreaded = 1; 219 220 pthread_attr_t thread_attr; 221 if (attr == NULL) { 222 pthread_attr_init(&thread_attr); 223 } else { 224 thread_attr = *attr; 225 attr = NULL; // Prevent misuse below. 226 } 227 228 pthread_internal_t* thread = NULL; 229 void* child_stack = NULL; 230 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 231 if (result != 0) { 232 return result; 233 } 234 235 // Create a lock for the thread to wait on once it starts so we can keep 236 // it from doing anything until after we notify the debugger about it 237 // 238 // This also provides the memory barrier we need to ensure that all 239 // memory accesses previously performed by this thread are visible to 240 // the new thread. 241 thread->startup_handshake_lock.init(false); 242 thread->startup_handshake_lock.lock(); 243 244 thread->start_routine = start_routine; 245 thread->start_routine_arg = arg; 246 247 thread->set_cached_pid(getpid()); 248 249 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 250 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 251 void* tls = reinterpret_cast<void*>(thread->tls); 252#if defined(__i386__) 253 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 254 // a pointer to the TLS itself. 255 user_desc tls_descriptor; 256 __init_user_desc(&tls_descriptor, false, tls); 257 tls = &tls_descriptor; 258#endif 259 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 260 if (rc == -1) { 261 int clone_errno = errno; 262 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 263 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 264 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 265 thread->startup_handshake_lock.unlock(); 266 if (thread->mmap_size != 0) { 267 munmap(thread->attr.stack_base, thread->mmap_size); 268 } 269 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 270 return clone_errno; 271 } 272 273 int init_errno = __init_thread(thread); 274 if (init_errno != 0) { 275 // Mark the thread detached and replace its start_routine with a no-op. 276 // Letting the thread run is the easiest way to clean up its resources. 277 atomic_store(&thread->join_state, THREAD_DETACHED); 278 __pthread_internal_add(thread); 279 thread->start_routine = __do_nothing; 280 thread->startup_handshake_lock.unlock(); 281 return init_errno; 282 } 283 284 // Publish the pthread_t and unlock the mutex to let the new thread start running. 285 *thread_out = __pthread_internal_add(thread); 286 thread->startup_handshake_lock.unlock(); 287 288 return 0; 289} 290