pthread_create.cpp revision b0e8c565a622b5519e03d4416b0b5b1a5f20d7f5
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 defined(__i386__) 48#include <asm/ldt.h> 49void __init_user_desc(struct user_desc*, bool, 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 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 57 thread->tls[TLS_SLOT_SELF] = thread->tls; 58 thread->tls[TLS_SLOT_THREAD_ID] = thread; 59} 60 61void __init_thread_stack_guard(pthread_internal_t* thread) { 62 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 63 thread->tls[TLS_SLOT_STACK_GUARD] = reinterpret_cast<void*>(__stack_chk_guard); 64} 65 66void __init_alternate_signal_stack(pthread_internal_t* thread) { 67 // Create and set an alternate signal stack. 68 void* stack_base = mmap(NULL, SIGNAL_STACK_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 69 if (stack_base != MAP_FAILED) { 70 71 // Create a guard page to catch stack overflows in signal handlers. 72 if (mprotect(stack_base, PAGE_SIZE, PROT_NONE) == -1) { 73 munmap(stack_base, SIGNAL_STACK_SIZE); 74 return; 75 } 76 stack_t ss; 77 ss.ss_sp = reinterpret_cast<uint8_t*>(stack_base) + PAGE_SIZE; 78 ss.ss_size = SIGNAL_STACK_SIZE - PAGE_SIZE; 79 ss.ss_flags = 0; 80 sigaltstack(&ss, NULL); 81 thread->alternate_signal_stack = stack_base; 82 83 // We can only use const static allocated string for mapped region name, as Android kernel 84 // uses the string pointer directly when dumping /proc/pid/maps. 85 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); 86 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, stack_base, PAGE_SIZE, "thread signal stack guard page"); 87 } 88} 89 90int __init_thread(pthread_internal_t* thread) { 91 int error = 0; 92 93 if (__predict_true((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) == 0)) { 94 atomic_init(&thread->join_state, THREAD_NOT_JOINED); 95 } else { 96 atomic_init(&thread->join_state, THREAD_DETACHED); 97 } 98 99 // Set the scheduling policy/priority of the thread. 100 if (thread->attr.sched_policy != SCHED_NORMAL) { 101 sched_param param; 102 param.sched_priority = thread->attr.sched_priority; 103 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 104#if defined(__LP64__) 105 // For backwards compatibility reasons, we only report failures on 64-bit devices. 106 error = errno; 107#endif 108 __libc_format_log(ANDROID_LOG_WARN, "libc", 109 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 110 } 111 } 112 113 thread->cleanup_stack = NULL; 114 115 return error; 116} 117 118void __free_thread(pthread_internal_t* thread) { 119 if (thread->mmap_size != 0) { 120 // Free mapped space, including thread stack and pthread_internal_t. 121 munmap(thread->attr.stack_base, thread->mmap_size); 122 } 123} 124 125static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 126 // Create a new private anonymous map. 127 int prot = PROT_READ | PROT_WRITE; 128 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 129 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 130 if (space == MAP_FAILED) { 131 __libc_format_log(ANDROID_LOG_WARN, 132 "libc", 133 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 134 mmap_size, strerror(errno)); 135 return NULL; 136 } 137 138 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 139 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 140 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 141 __libc_format_log(ANDROID_LOG_WARN, "libc", 142 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 143 stack_guard_size, strerror(errno)); 144 munmap(space, mmap_size); 145 return NULL; 146 } 147 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, space, stack_guard_size, "thread stack guard page"); 148 149 return space; 150} 151 152static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 153 size_t mmap_size; 154 uint8_t* stack_top; 155 156 if (attr->stack_base == NULL) { 157 // The caller didn't provide a stack, so allocate one. 158 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 159 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 160 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 161 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 162 if (attr->stack_base == NULL) { 163 return EAGAIN; 164 } 165 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 166 } else { 167 // Remember the mmap size is zero and we don't need to free it. 168 mmap_size = 0; 169 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 170 } 171 172 // Mapped space(or user allocated stack) is used for: 173 // pthread_internal_t 174 // thread stack (including guard page) 175 176 // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary. 177 stack_top = reinterpret_cast<uint8_t*>( 178 (reinterpret_cast<uintptr_t>(stack_top) - sizeof(pthread_internal_t)) & ~0xf); 179 180 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 181 if (mmap_size == 0) { 182 // If thread was not allocated by mmap(), it may not have been cleared to zero. 183 // So assume the worst and zero it. 184 memset(thread, 0, sizeof(pthread_internal_t)); 185 } 186 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base); 187 188 thread->mmap_size = mmap_size; 189 thread->attr = *attr; 190 __init_tls(thread); 191 __init_thread_stack_guard(thread); 192 193 *threadp = thread; 194 *child_stack = stack_top; 195 return 0; 196} 197 198static int __pthread_start(void* arg) { 199 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 200 201 // Wait for our creating thread to release us. This lets it have time to 202 // notify gdb about this thread before we start doing anything. 203 // This also provides the memory barrier needed to ensure that all memory 204 // accesses previously made by the creating thread are visible to us. 205 thread->startup_handshake_lock.lock(); 206 207 __init_alternate_signal_stack(thread); 208 209 void* result = thread->start_routine(thread->start_routine_arg); 210 pthread_exit(result); 211 212 return 0; 213} 214 215// A dummy start routine for pthread_create failures where we've created a thread but aren't 216// going to run user code on it. We swap out the user's start routine for this and take advantage 217// of the regular thread teardown to free up resources. 218static void* __do_nothing(void*) { 219 return NULL; 220} 221 222int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 223 void* (*start_routine)(void*), void* arg) { 224 ErrnoRestorer errno_restorer; 225 226 // Inform the rest of the C library that at least one thread was created. 227 __isthreaded = 1; 228 229 pthread_attr_t thread_attr; 230 if (attr == NULL) { 231 pthread_attr_init(&thread_attr); 232 } else { 233 thread_attr = *attr; 234 attr = NULL; // Prevent misuse below. 235 } 236 237 pthread_internal_t* thread = NULL; 238 void* child_stack = NULL; 239 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 240 if (result != 0) { 241 return result; 242 } 243 244 // Create a lock for the thread to wait on once it starts so we can keep 245 // it from doing anything until after we notify the debugger about it 246 // 247 // This also provides the memory barrier we need to ensure that all 248 // memory accesses previously performed by this thread are visible to 249 // the new thread. 250 thread->startup_handshake_lock.init(false); 251 thread->startup_handshake_lock.lock(); 252 253 thread->start_routine = start_routine; 254 thread->start_routine_arg = arg; 255 256 thread->set_cached_pid(getpid()); 257 258 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 259 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 260 void* tls = reinterpret_cast<void*>(thread->tls); 261#if defined(__i386__) 262 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 263 // a pointer to the TLS itself. 264 user_desc tls_descriptor; 265 __init_user_desc(&tls_descriptor, false, tls); 266 tls = &tls_descriptor; 267#endif 268 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 269 if (rc == -1) { 270 int clone_errno = errno; 271 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 272 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 273 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 274 thread->startup_handshake_lock.unlock(); 275 __free_thread(thread); 276 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 277 return clone_errno; 278 } 279 280 int init_errno = __init_thread(thread); 281 if (init_errno != 0) { 282 // Mark the thread detached and replace its start_routine with a no-op. 283 // Letting the thread run is the easiest way to clean up its resources. 284 atomic_store(&thread->join_state, THREAD_DETACHED); 285 thread->start_routine = __do_nothing; 286 thread->startup_handshake_lock.unlock(); 287 return init_errno; 288 } 289 290 // Publish the pthread_t and unlock the mutex to let the new thread start running. 291 *thread_out = reinterpret_cast<pthread_t>(thread); 292 thread->startup_handshake_lock.unlock(); 293 294 return 0; 295} 296