pthread_create.cpp revision ba8dfc2669d658dc340eb8f9c9b40ca074f05047
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 <sys/mman.h> 33#include <unistd.h> 34 35#include "pthread_internal.h" 36 37#include "private/bionic_macros.h" 38#include "private/bionic_prctl.h" 39#include "private/bionic_ssp.h" 40#include "private/bionic_tls.h" 41#include "private/libc_logging.h" 42#include "private/ErrnoRestorer.h" 43#include "private/ScopedPthreadMutexLocker.h" 44 45// x86 uses segment descriptors rather than a direct pointer to TLS. 46#if __i386__ 47#include <asm/ldt.h> 48extern "C" __LIBC_HIDDEN__ void __init_user_desc(struct user_desc*, int, void*); 49#endif 50 51extern "C" int __isthreaded; 52 53// This code is used both by each new pthread and the code that initializes the main thread. 54void __init_tls(pthread_internal_t* thread) { 55 if (thread->mmap_size == 0) { 56 // If the TLS area was not allocated by mmap(), it may not have been cleared to zero. 57 // So assume the worst and zero the TLS area. 58 memset(&thread->tls[0], 0, BIONIC_TLS_SLOTS * sizeof(void*)); 59 } 60 61 // Slot 0 must point to itself. The x86 Linux kernel reads the TLS from %fs:0. 62 thread->tls[TLS_SLOT_SELF] = thread->tls; 63 thread->tls[TLS_SLOT_THREAD_ID] = thread; 64 // GCC looks in the TLS for the stack guard on x86, so copy it there from our global. 65 thread->tls[TLS_SLOT_STACK_GUARD] = (void*) __stack_chk_guard; 66} 67 68void __init_alternate_signal_stack(pthread_internal_t* thread) { 69 // Create and set an alternate signal stack. 70 stack_t ss; 71 ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 72 if (ss.ss_sp != MAP_FAILED) { 73 ss.ss_size = SIGSTKSZ; 74 ss.ss_flags = 0; 75 sigaltstack(&ss, NULL); 76 thread->alternate_signal_stack = ss.ss_sp; 77 78 // We can only use const static allocated string for mapped region name, as Android kernel 79 // uses the string pointer directly when dumping /proc/pid/maps. 80 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); 81 } 82} 83 84int __init_thread(pthread_internal_t* thread, bool add_to_thread_list) { 85 int error = 0; 86 87 // Set the scheduling policy/priority of the thread. 88 if (thread->attr.sched_policy != SCHED_NORMAL) { 89 sched_param param; 90 param.sched_priority = thread->attr.sched_priority; 91 if (sched_setscheduler(thread->tid, thread->attr.sched_policy, ¶m) == -1) { 92#if __LP64__ 93 // For backwards compatibility reasons, we only report failures on 64-bit devices. 94 error = errno; 95#endif 96 __libc_format_log(ANDROID_LOG_WARN, "libc", 97 "pthread_create sched_setscheduler call failed: %s", strerror(errno)); 98 } 99 } 100 101 thread->cleanup_stack = NULL; 102 103 if (add_to_thread_list) { 104 _pthread_internal_add(thread); 105 } 106 107 return error; 108} 109 110static void* __create_thread_mapped_space(size_t mmap_size, size_t stack_guard_size) { 111 // Create a new private anonymous map. 112 int prot = PROT_READ | PROT_WRITE; 113 int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE; 114 void* space = mmap(NULL, mmap_size, prot, flags, -1, 0); 115 if (space == MAP_FAILED) { 116 __libc_format_log(ANDROID_LOG_WARN, 117 "libc", 118 "pthread_create failed: couldn't allocate %zu-bytes mapped space: %s", 119 mmap_size, strerror(errno)); 120 return NULL; 121 } 122 123 // Stack is at the lower end of mapped space, stack guard region is at the lower end of stack. 124 // Set the stack guard region to PROT_NONE, so we can detect thread stack overflow. 125 if (mprotect(space, stack_guard_size, PROT_NONE) == -1) { 126 __libc_format_log(ANDROID_LOG_WARN, "libc", 127 "pthread_create failed: couldn't mprotect PROT_NONE %zu-byte stack guard region: %s", 128 stack_guard_size, strerror(errno)); 129 munmap(space, mmap_size); 130 return NULL; 131 } 132 133 return space; 134} 135 136static int __allocate_thread(pthread_attr_t* attr, pthread_internal_t** threadp, void** child_stack) { 137 size_t mmap_size; 138 uint8_t* stack_top; 139 140 if (attr->stack_base == NULL) { 141 // The caller didn't provide a stack, so allocate one. 142 // Make sure the stack size and guard size are multiples of PAGE_SIZE. 143 mmap_size = BIONIC_ALIGN(attr->stack_size + sizeof(pthread_internal_t), PAGE_SIZE); 144 attr->guard_size = BIONIC_ALIGN(attr->guard_size, PAGE_SIZE); 145 attr->stack_base = __create_thread_mapped_space(mmap_size, attr->guard_size); 146 if (attr->stack_base == NULL) { 147 return EAGAIN; 148 } 149 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + mmap_size; 150 } else { 151 // Remember the mmap size is zero and we don't need to free it. 152 mmap_size = 0; 153 stack_top = reinterpret_cast<uint8_t*>(attr->stack_base) + attr->stack_size; 154 } 155 156 // Mapped space(or user allocated stack) is used for: 157 // thread_internal_t (including tls array) 158 // thread stack (including guard page) 159 stack_top -= sizeof(pthread_internal_t); 160 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top); 161 162 // No need to check stack_top alignment. The size of pthread_internal_t is 16-bytes aligned, 163 // and user allocated stack is guaranteed by pthread_attr_setstack. 164 165 thread->mmap_size = mmap_size; 166 thread->attr = *attr; 167 __init_tls(thread); 168 169 *threadp = thread; 170 *child_stack = stack_top; 171 return 0; 172} 173 174static int __pthread_start(void* arg) { 175 pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg); 176 177 // Wait for our creating thread to release us. This lets it have time to 178 // notify gdb about this thread before we start doing anything. 179 // This also provides the memory barrier needed to ensure that all memory 180 // accesses previously made by the creating thread are visible to us. 181 pthread_mutex_lock(&thread->startup_handshake_mutex); 182 pthread_mutex_destroy(&thread->startup_handshake_mutex); 183 184 __init_alternate_signal_stack(thread); 185 186 void* result = thread->start_routine(thread->start_routine_arg); 187 pthread_exit(result); 188 189 return 0; 190} 191 192// A dummy start routine for pthread_create failures where we've created a thread but aren't 193// going to run user code on it. We swap out the user's start routine for this and take advantage 194// of the regular thread teardown to free up resources. 195static void* __do_nothing(void*) { 196 return NULL; 197} 198 199int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, 200 void* (*start_routine)(void*), void* arg) { 201 ErrnoRestorer errno_restorer; 202 203 // Inform the rest of the C library that at least one thread was created. 204 __isthreaded = 1; 205 206 pthread_attr_t thread_attr; 207 if (attr == NULL) { 208 pthread_attr_init(&thread_attr); 209 } else { 210 thread_attr = *attr; 211 attr = NULL; // Prevent misuse below. 212 } 213 214 pthread_internal_t* thread = NULL; 215 void* child_stack = NULL; 216 int result = __allocate_thread(&thread_attr, &thread, &child_stack); 217 if (result != 0) { 218 return result; 219 } 220 221 // Create a mutex for the thread in TLS to wait on once it starts so we can keep 222 // it from doing anything until after we notify the debugger about it 223 // 224 // This also provides the memory barrier we need to ensure that all 225 // memory accesses previously performed by this thread are visible to 226 // the new thread. 227 pthread_mutex_init(&thread->startup_handshake_mutex, NULL); 228 pthread_mutex_lock(&thread->startup_handshake_mutex); 229 230 thread->start_routine = start_routine; 231 thread->start_routine_arg = arg; 232 233 thread->set_cached_pid(getpid()); 234 235 int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | 236 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; 237 void* tls = reinterpret_cast<void*>(thread->tls); 238#if defined(__i386__) 239 // On x86 (but not x86-64), CLONE_SETTLS takes a pointer to a struct user_desc rather than 240 // a pointer to the TLS itself. 241 user_desc tls_descriptor; 242 __init_user_desc(&tls_descriptor, false, tls); 243 tls = &tls_descriptor; 244#endif 245 int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid)); 246 if (rc == -1) { 247 int clone_errno = errno; 248 // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to 249 // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a 250 // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. 251 pthread_mutex_unlock(&thread->startup_handshake_mutex); 252 if (thread->mmap_size != 0) { 253 munmap(thread->attr.stack_base, thread->mmap_size); 254 } 255 __libc_format_log(ANDROID_LOG_WARN, "libc", "pthread_create failed: clone failed: %s", strerror(errno)); 256 return clone_errno; 257 } 258 259 int init_errno = __init_thread(thread, true); 260 if (init_errno != 0) { 261 // Mark the thread detached and replace its start_routine with a no-op. 262 // Letting the thread run is the easiest way to clean up its resources. 263 thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; 264 thread->start_routine = __do_nothing; 265 pthread_mutex_unlock(&thread->startup_handshake_mutex); 266 return init_errno; 267 } 268 269 // Publish the pthread_t and unlock the mutex to let the new thread start running. 270 *thread_out = reinterpret_cast<pthread_t>(thread); 271 pthread_mutex_unlock(&thread->startup_handshake_mutex); 272 273 return 0; 274} 275