pthread_create.cpp revision 05fc1d7050d5451aea08dc5f504d2670287b2d43
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], 0, BIONIC_TLS_SLOTS * sizeof(void*)); 60 } 61 62 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 63 thread->tls[TLS_SLOT_SELF] = thread->tls; 64 thread->tls[TLS_SLOT_THREAD_ID] = thread; 65 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 66 thread->tls[TLS_SLOT_STACK_GUARD] = reinterpret_cast<void*>(__stack_chk_guard); 67} 68 69void __init_alternate_signal_stack(pthread_internal_t* thread) { 70 // Create and set an alternate signal stack. 71 stack_t ss; 72 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 73 if (ss.ss_sp != MAP_FAILED) { 74 ss.ss_size = SIGSTKSZ; 75 ss.ss_flags = 0; 76 sigaltstack(&ss, NULL); 77 thread->alternate_signal_stack = ss.ss_sp; 78 79 // We can only use const static allocated string for mapped region name, as Android kernel 80 // uses the string pointer directly when dumping /proc/pid/maps. 81 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); 82 } 83} 84 85int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) { 86 int error = 0; 87 88 // Set the scheduling policy/priority of the thread. 89 if (thread->attr.sched_policy != SCHED_NORMAL) { 90 sched_param param; 91 param.sched_priority = thread->attr.sched_priority; 92 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 93#if __LP64__ 94 // For backwards compatibility reasons, we only report failures on 64-bit devices. 95 error = errno; 96#endif 97 __libc_format_log(ANDROID_LOG_WARN, "libc", 98 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 99 } 100 } 101 102 thread->cleanup_stack = NULL; 103 104 if (add_to_thread_list) { 105 _pthread_internal_add(thread); 106 } 107 108 return error; 109} 110 111static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 112 // Create a new private anonymous map. 113 int prot = PROT_READ | PROT_WRITE; 114 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 115 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 116 if (space == MAP_FAILED) { 117 __libc_format_log(ANDROID_LOG_WARN, 118 "libc", 119 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 120 mmap_size, strerror(errno)); 121 return NULL; 122 } 123 124 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 125 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 126 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 127 __libc_format_log(ANDROID_LOG_WARN, "libc", 128 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 129 stack_guard_size, strerror(errno)); 130 munmap(space, mmap_size); 131 return NULL; 132 } 133 134 return space; 135} 136 137static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 138 size_t mmap_size; 139 uint8_t* stack_top; 140 141 if (attr->stack_base == NULL) { 142 // The caller didn't provide a stack, so allocate one. 143 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 144 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 145 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 146 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 147 if (attr->stack_base == NULL) { 148 return EAGAIN; 149 } 150 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 151 } else { 152 // Remember the mmap size is zero and we don't need to free it. 153 mmap_size = 0; 154 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 155 } 156 157 // Mapped space(or user allocated stack) is used for: 158 // thread_internal_t (including tls array) 159 // thread stack (including guard page) 160 stack_top -= sizeof(pthread_internal_t); 161 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 162 attr->stack_size = stack_top - reinterpret_cast<uint8_t*>(attr->stack_base); 163 164 // No need to check stack_top alignment. The size of pthread_internal_t is 16-bytes aligned, 165 // and user allocated stack is guaranteed by pthread_attr_setstack. 166 167 thread->mmap_size = mmap_size; 168 thread->attr = *attr; 169 __init_tls(thread); 170 171 *threadp = thread; 172 *child_stack = stack_top; 173 return 0; 174} 175 176static int __pthread_start(void* arg) { 177 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 178 179 // Wait for our creating thread to release us. This lets it have time to 180 // notify gdb about this thread before we start doing anything. 181 // This also provides the memory barrier needed to ensure that all memory 182 // accesses previously made by the creating thread are visible to us. 183 pthread_mutex_lock(&thread->startup_handshake_mutex); 184 pthread_mutex_destroy(&thread->startup_handshake_mutex); 185 186 __init_alternate_signal_stack(thread); 187 188 void* result = thread->start_routine(thread->start_routine_arg); 189 pthread_exit(result); 190 191 return 0; 192} 193 194// A dummy start routine for pthread_create failures where we've created a thread but aren't 195// going to run user code on it. We swap out the user's start routine for this and take advantage 196// of the regular thread teardown to free up resources. 197static void* __do_nothing(void*) { 198 return NULL; 199} 200 201int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 202 void* (*start_routine)(void*), void* arg) { 203 ErrnoRestorer errno_restorer; 204 205 // Inform the rest of the C library that at least one thread was created. 206 __isthreaded = 1; 207 208 pthread_attr_t thread_attr; 209 if (attr == NULL) { 210 pthread_attr_init(&thread_attr); 211 } else { 212 thread_attr = *attr; 213 attr = NULL; // Prevent misuse below. 214 } 215 216 pthread_internal_t* thread = NULL; 217 void* child_stack = NULL; 218 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 219 if (result != 0) { 220 return result; 221 } 222 223 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 224 // it from doing anything until after we notify the debugger about it 225 // 226 // This also provides the memory barrier we need to ensure that all 227 // memory accesses previously performed by this thread are visible to 228 // the new thread. 229 pthread_mutex_init(&thread->startup_handshake_mutex, NULL); 230 pthread_mutex_lock(&thread->startup_handshake_mutex); 231 232 thread->start_routine = start_routine; 233 thread->start_routine_arg = arg; 234 235 thread->set_cached_pid(getpid()); 236 237 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 238 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 239 void* tls = reinterpret_cast<void*>(thread->tls); 240#if defined(__i386__) 241 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 242 // a pointer to the TLS itself. 243 user_desc tls_descriptor; 244 __init_user_desc(&tls_descriptor, false, tls); 245 tls = &tls_descriptor; 246#endif 247 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 248 if (rc == -1) { 249 int clone_errno = errno; 250 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 251 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 252 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 253 pthread_mutex_unlock(&thread->startup_handshake_mutex); 254 if (thread->mmap_size != 0) { 255 munmap(thread->attr.stack_base, thread->mmap_size); 256 } 257 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 258 return clone_errno; 259 } 260 261 int init_errno = __init_thread(thread, true); 262 if (init_errno != 0) { 263 // Mark the thread detached and replace its start_routine with a no-op. 264 // Letting the thread run is the easiest way to clean up its resources. 265 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 266 thread->start_routine = __do_nothing; 267 pthread_mutex_unlock(&thread->startup_handshake_mutex); 268 return init_errno; 269 } 270 271 // Publish the pthread_t and unlock the mutex to let the new thread start running. 272 *thread_out = reinterpret_cast<pthread_t>(thread); 273 pthread_mutex_unlock(&thread->startup_handshake_mutex); 274 275 return 0; 276} 277