pthread_create.cpp revision b36efa4343d79e3fb548d12d039193850246b892
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> 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 118static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 119 // Create a new private anonymous map. 120 int prot = PROT_READ | PROT_WRITE; 121 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 122 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 123 if (space == MAP_FAILED) { 124 __libc_format_log(ANDROID_LOG_WARN, 125 "libc", 126 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 127 mmap_size, strerror(errno)); 128 return NULL; 129 } 130 131 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 132 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 133 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 134 __libc_format_log(ANDROID_LOG_WARN, "libc", 135 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 136 stack_guard_size, strerror(errno)); 137 munmap(space, mmap_size); 138 return NULL; 139 } 140 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, space, stack_guard_size, "thread stack guard page"); 141 142 return space; 143} 144 145static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 146 size_t mmap_size; 147 uint8_t* stack_top; 148 149 if (attr->stack_base == NULL) { 150 // The caller didn't provide a stack, so allocate one. 151 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 152 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 153 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 154 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 155 if (attr->stack_base == NULL) { 156 return EAGAIN; 157 } 158 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 159 } else { 160 // Remember the mmap size is zero and we don't need to free it. 161 mmap_size = 0; 162 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 163 } 164 165 // Mapped space(or user allocated stack) is used for: 166 // pthread_internal_t 167 // thread stack (including guard page) 168 169 // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary. 170 stack_top = reinterpret_cast<uint8_t*>( 171 (reinterpret_cast<uintptr_t>(stack_top) - sizeof(pthread_internal_t)) & ~0xf); 172 173 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 174 if (mmap_size == 0) { 175 // If thread was not allocated by mmap(), it may not have been cleared to zero. 176 // So assume the worst and zero it. 177 memset(thread, 0, sizeof(pthread_internal_t)); 178 } 179 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base); 180 181 thread->mmap_size = mmap_size; 182 thread->attr = *attr; 183 __init_tls(thread); 184 __init_thread_stack_guard(thread); 185 186 *threadp = thread; 187 *child_stack = stack_top; 188 return 0; 189} 190 191static int __pthread_start(void* arg) { 192 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 193 194 // Wait for our creating thread to release us. This lets it have time to 195 // notify gdb about this thread before we start doing anything. 196 // This also provides the memory barrier needed to ensure that all memory 197 // accesses previously made by the creating thread are visible to us. 198 thread->startup_handshake_lock.lock(); 199 200 __init_alternate_signal_stack(thread); 201 202 void* result = thread->start_routine(thread->start_routine_arg); 203 pthread_exit(result); 204 205 return 0; 206} 207 208// A dummy start routine for pthread_create failures where we've created a thread but aren't 209// going to run user code on it. We swap out the user's start routine for this and take advantage 210// of the regular thread teardown to free up resources. 211static void* __do_nothing(void*) { 212 return NULL; 213} 214 215int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 216 void* (*start_routine)(void*), void* arg) { 217 ErrnoRestorer errno_restorer; 218 219 // Inform the rest of the C library that at least one thread was created. 220 __isthreaded = 1; 221 222 pthread_attr_t thread_attr; 223 if (attr == NULL) { 224 pthread_attr_init(&thread_attr); 225 } else { 226 thread_attr = *attr; 227 attr = NULL; // Prevent misuse below. 228 } 229 230 pthread_internal_t* thread = NULL; 231 void* child_stack = NULL; 232 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 233 if (result != 0) { 234 return result; 235 } 236 237 // Create a lock for the thread to wait on once it starts so we can keep 238 // it from doing anything until after we notify the debugger about it 239 // 240 // This also provides the memory barrier we need to ensure that all 241 // memory accesses previously performed by this thread are visible to 242 // the new thread. 243 thread->startup_handshake_lock.init(false); 244 thread->startup_handshake_lock.lock(); 245 246 thread->start_routine = start_routine; 247 thread->start_routine_arg = arg; 248 249 thread->set_cached_pid(getpid()); 250 251 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 252 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 253 void* tls = reinterpret_cast<void*>(thread->tls); 254#if defined(__i386__) 255 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 256 // a pointer to the TLS itself. 257 user_desc tls_descriptor; 258 __init_user_desc(&tls_descriptor, false, tls); 259 tls = &tls_descriptor; 260#endif 261 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 262 if (rc == -1) { 263 int clone_errno = errno; 264 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 265 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 266 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 267 thread->startup_handshake_lock.unlock(); 268 if (thread->mmap_size != 0) { 269 munmap(thread->attr.stack_base, thread->mmap_size); 270 } 271 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 272 return clone_errno; 273 } 274 275 int init_errno = __init_thread(thread); 276 if (init_errno != 0) { 277 // Mark the thread detached and replace its start_routine with a no-op. 278 // Letting the thread run is the easiest way to clean up its resources. 279 atomic_store(&thread->join_state, THREAD_DETACHED); 280 __pthread_internal_add(thread); 281 thread->start_routine = __do_nothing; 282 thread->startup_handshake_lock.unlock(); 283 return init_errno; 284 } 285 286 // Publish the pthread_t and unlock the mutex to let the new thread start running. 287 *thread_out = __pthread_internal_add(thread); 288 thread->startup_handshake_lock.unlock(); 289 290 return 0; 291} 292