diff options
Diffstat (limited to 'libc')
| -rw-r--r-- | libc/SYSCALLS.TXT | 1 | ||||
| -rw-r--r-- | libc/arch-aarch64/syscalls.mk | 1 | ||||
| -rw-r--r-- | libc/arch-aarch64/syscalls/__set_tid_address.S | 22 | ||||
| -rw-r--r-- | libc/arch-arm/syscalls.mk | 1 | ||||
| -rw-r--r-- | libc/arch-arm/syscalls/__set_tid_address.S | 14 | ||||
| -rw-r--r-- | libc/arch-mips/syscalls.mk | 1 | ||||
| -rw-r--r-- | libc/arch-mips/syscalls/__set_tid_address.S | 23 | ||||
| -rw-r--r-- | libc/arch-x86/syscalls.mk | 1 | ||||
| -rw-r--r-- | libc/arch-x86/syscalls/__set_tid_address.S | 20 | ||||
| -rw-r--r-- | libc/arch-x86_64/syscalls.mk | 1 | ||||
| -rw-r--r-- | libc/arch-x86_64/syscalls/__set_tid_address.S | 17 | ||||
| -rw-r--r-- | libc/bionic/fork.cpp | 7 | ||||
| -rw-r--r-- | libc/bionic/libc_init_common.cpp | 26 | ||||
| -rw-r--r-- | libc/bionic/pthread_create.cpp | 25 | ||||
| -rw-r--r-- | libc/bionic/pthread_exit.cpp | 21 | ||||
| -rw-r--r-- | libc/bionic/pthread_internal.h | 48 | ||||
| -rw-r--r-- | libc/bionic/pthread_join.cpp | 47 | ||||
| -rw-r--r-- | libc/bionic/pthread_key.cpp | 2 | ||||
| -rw-r--r-- | libc/private/bionic_futex.h | 1 | ||||
| -rw-r--r-- | libc/private/bionic_tls.h | 4 |
20 files changed, 207 insertions, 76 deletions
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT index 533116e..a027024 100644 --- a/libc/SYSCALLS.TXT +++ b/libc/SYSCALLS.TXT @@ -276,6 +276,7 @@ int personality(unsigned long) all long perf_event_open(struct perf_event_attr* attr_uptr, pid_t pid, int cpu, int group_fd, unsigned long flags) all pid_t __clone:clone(int, void*, int*, void*, int*) all +int __set_tid_address:set_tid_address(int*) all int epoll_create1(int) all int epoll_ctl(int, int op, int, struct epoll_event*) all diff --git a/libc/arch-aarch64/syscalls.mk b/libc/arch-aarch64/syscalls.mk index 995d44a..890a6d8 100644 --- a/libc/arch-aarch64/syscalls.mk +++ b/libc/arch-aarch64/syscalls.mk @@ -19,6 +19,7 @@ syscall_src += arch-aarch64/syscalls/__rt_sigprocmask.S syscall_src += arch-aarch64/syscalls/__rt_sigsuspend.S syscall_src += arch-aarch64/syscalls/__rt_sigtimedwait.S syscall_src += arch-aarch64/syscalls/__sched_getaffinity.S +syscall_src += arch-aarch64/syscalls/__set_tid_address.S syscall_src += arch-aarch64/syscalls/__syslog.S syscall_src += arch-aarch64/syscalls/__timer_create.S syscall_src += arch-aarch64/syscalls/__timer_delete.S diff --git a/libc/arch-aarch64/syscalls/__set_tid_address.S b/libc/arch-aarch64/syscalls/__set_tid_address.S new file mode 100644 index 0000000..b7541fc --- /dev/null +++ b/libc/arch-aarch64/syscalls/__set_tid_address.S @@ -0,0 +1,22 @@ +/* Generated by gensyscalls.py. Do not edit. */ + +#include <private/bionic_asm.h> + +ENTRY(__set_tid_address) + stp x29, x30, [sp, #-16]! + mov x29, sp + str x8, [sp, #-16]! + + mov x8, __NR_set_tid_address + svc #0 + + ldr x8, [sp], #16 + ldp x29, x30, [sp], #16 + + cmn x0, #(MAX_ERRNO + 1) + cneg x0, x0, hi + b.hi __set_errno + + ret +END(__set_tid_address) +.hidden _C_LABEL(__set_tid_address) diff --git a/libc/arch-arm/syscalls.mk b/libc/arch-arm/syscalls.mk index 75b6133..f8bb15a 100644 --- a/libc/arch-arm/syscalls.mk +++ b/libc/arch-arm/syscalls.mk @@ -23,6 +23,7 @@ syscall_src += arch-arm/syscalls/__rt_sigprocmask.S syscall_src += arch-arm/syscalls/__rt_sigsuspend.S syscall_src += arch-arm/syscalls/__rt_sigtimedwait.S syscall_src += arch-arm/syscalls/__sched_getaffinity.S +syscall_src += arch-arm/syscalls/__set_tid_address.S syscall_src += arch-arm/syscalls/__set_tls.S syscall_src += arch-arm/syscalls/__sigaction.S syscall_src += arch-arm/syscalls/__statfs64.S diff --git a/libc/arch-arm/syscalls/__set_tid_address.S b/libc/arch-arm/syscalls/__set_tid_address.S new file mode 100644 index 0000000..b4b42e7 --- /dev/null +++ b/libc/arch-arm/syscalls/__set_tid_address.S @@ -0,0 +1,14 @@ +/* Generated by gensyscalls.py. Do not edit. */ + +#include <private/bionic_asm.h> + +ENTRY(__set_tid_address) + mov ip, r7 + ldr r7, =__NR_set_tid_address + swi #0 + mov r7, ip + cmn r0, #(MAX_ERRNO + 1) + bxls lr + neg r0, r0 + b __set_errno +END(__set_tid_address) diff --git a/libc/arch-mips/syscalls.mk b/libc/arch-mips/syscalls.mk index e141a65..6b72e70 100644 --- a/libc/arch-mips/syscalls.mk +++ b/libc/arch-mips/syscalls.mk @@ -24,6 +24,7 @@ syscall_src += arch-mips/syscalls/__rt_sigsuspend.S syscall_src += arch-mips/syscalls/__rt_sigtimedwait.S syscall_src += arch-mips/syscalls/__sched_getaffinity.S syscall_src += arch-mips/syscalls/__set_thread_area.S +syscall_src += arch-mips/syscalls/__set_tid_address.S syscall_src += arch-mips/syscalls/__sigaction.S syscall_src += arch-mips/syscalls/__statfs64.S syscall_src += arch-mips/syscalls/__syslog.S diff --git a/libc/arch-mips/syscalls/__set_tid_address.S b/libc/arch-mips/syscalls/__set_tid_address.S new file mode 100644 index 0000000..4fcc82a --- /dev/null +++ b/libc/arch-mips/syscalls/__set_tid_address.S @@ -0,0 +1,23 @@ +/* Generated by gensyscalls.py. Do not edit. */ + +#include <asm/unistd.h> + .text + .globl __set_tid_address + .align 4 + .ent __set_tid_address + +__set_tid_address: + .set noreorder + .cpload $t9 + li $v0, __NR_set_tid_address + syscall + bnez $a3, 1f + move $a0, $v0 + j $ra + nop +1: + la $t9,__set_errno + j $t9 + nop + .set reorder + .end __set_tid_address diff --git a/libc/arch-x86/syscalls.mk b/libc/arch-x86/syscalls.mk index 70e6e39..b6a1e38 100644 --- a/libc/arch-x86/syscalls.mk +++ b/libc/arch-x86/syscalls.mk @@ -24,6 +24,7 @@ syscall_src += arch-x86/syscalls/__rt_sigsuspend.S syscall_src += arch-x86/syscalls/__rt_sigtimedwait.S syscall_src += arch-x86/syscalls/__sched_getaffinity.S syscall_src += arch-x86/syscalls/__set_thread_area.S +syscall_src += arch-x86/syscalls/__set_tid_address.S syscall_src += arch-x86/syscalls/__sigaction.S syscall_src += arch-x86/syscalls/__statfs64.S syscall_src += arch-x86/syscalls/__syslog.S diff --git a/libc/arch-x86/syscalls/__set_tid_address.S b/libc/arch-x86/syscalls/__set_tid_address.S new file mode 100644 index 0000000..0c66d47 --- /dev/null +++ b/libc/arch-x86/syscalls/__set_tid_address.S @@ -0,0 +1,20 @@ +/* Generated by gensyscalls.py. Do not edit. */ + +#include <private/bionic_asm.h> + +ENTRY(__set_tid_address) + pushl %ebx + mov 8(%esp), %ebx + movl $__NR_set_tid_address, %eax + int $0x80 + cmpl $-MAX_ERRNO, %eax + jb 1f + negl %eax + pushl %eax + call __set_errno + addl $4, %esp + orl $-1, %eax +1: + popl %ebx + ret +END(__set_tid_address) diff --git a/libc/arch-x86_64/syscalls.mk b/libc/arch-x86_64/syscalls.mk index c874b61..50d9ab3 100644 --- a/libc/arch-x86_64/syscalls.mk +++ b/libc/arch-x86_64/syscalls.mk @@ -20,6 +20,7 @@ syscall_src += arch-x86_64/syscalls/__rt_sigprocmask.S syscall_src += arch-x86_64/syscalls/__rt_sigsuspend.S syscall_src += arch-x86_64/syscalls/__rt_sigtimedwait.S syscall_src += arch-x86_64/syscalls/__sched_getaffinity.S +syscall_src += arch-x86_64/syscalls/__set_tid_address.S syscall_src += arch-x86_64/syscalls/__syslog.S syscall_src += arch-x86_64/syscalls/__timer_create.S syscall_src += arch-x86_64/syscalls/__timer_delete.S diff --git a/libc/arch-x86_64/syscalls/__set_tid_address.S b/libc/arch-x86_64/syscalls/__set_tid_address.S new file mode 100644 index 0000000..fe7260f --- /dev/null +++ b/libc/arch-x86_64/syscalls/__set_tid_address.S @@ -0,0 +1,17 @@ +/* Generated by gensyscalls.py. Do not edit. */ + +#include <private/bionic_asm.h> + +ENTRY(__set_tid_address) + movl $__NR_set_tid_address, %eax + syscall + cmpq $-MAX_ERRNO, %rax + jb 1f + negl %eax + movl %eax, %edi + call __set_errno + orq $-1, %rax +1: + ret +END(__set_tid_address) +.hidden _C_LABEL(__set_tid_address) diff --git a/libc/bionic/fork.cpp b/libc/bionic/fork.cpp index 339a0e8..f7d1c11 100644 --- a/libc/bionic/fork.cpp +++ b/libc/bionic/fork.cpp @@ -41,7 +41,12 @@ int fork() { __timer_table_start_stop(1); __bionic_atfork_run_prepare(); - int result = __clone(SIGCHLD, NULL, NULL, NULL, NULL); + pthread_internal_t* self = __get_thread(); +#if defined(__x86_64__) + int result = __clone(CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID | SIGCHLD, NULL, NULL, &(self->tid), NULL); +#else + int result = __clone(CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID | SIGCHLD, NULL, NULL, NULL, &(self->tid)); +#endif if (result != 0) { // Not a child process. __timer_table_start_stop(0); __bionic_atfork_run_parent(); diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp index 3e092ae..130c287 100644 --- a/libc/bionic/libc_init_common.cpp +++ b/libc/bionic/libc_init_common.cpp @@ -50,6 +50,7 @@ extern "C" abort_msg_t** __abort_message_ptr; extern "C" uintptr_t __get_sp(void); extern "C" int __system_properties_init(void); extern "C" int __set_tls(void* ptr); +extern "C" int __set_tid_address(int* tid_address); // Not public, but well-known in the BSDs. const char* __progname; @@ -90,17 +91,24 @@ void __libc_init_tls(KernelArgumentBlock& args) { uintptr_t stack_bottom = stack_top - stack_size; static void* tls[BIONIC_TLS_SLOTS]; - static pthread_internal_t thread; - thread.tid = gettid(); - thread.tls = tls; - pthread_attr_init(&thread.attr); - pthread_attr_setstack(&thread.attr, (void*) stack_bottom, stack_size); - _init_thread(&thread, false); - __init_tls(&thread); - __set_tls(thread.tls); + static pthread_internal_t main_thread; + main_thread.tls = tls; + + // Tell the kernel to clear our tid field when we exit, so we're like any other pthread. + main_thread.tid = __set_tid_address(&main_thread.tid); + + // We already have a stack, and we don't want to free it up on exit (because things like + // environment variables with global scope live on it). + pthread_attr_init(&main_thread.attr); + pthread_attr_setstack(&main_thread.attr, (void*) stack_bottom, stack_size); + main_thread.attr.flags = PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK; + + _init_thread(&main_thread, false); + __init_tls(&main_thread); + __set_tls(main_thread.tls); tls[TLS_SLOT_BIONIC_PREINIT] = &args; - __init_alternate_signal_stack(&thread); + __init_alternate_signal_stack(&main_thread); } void __libc_init_common(KernelArgumentBlock& args) { diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp index 6ed01ff..dde5ed7 100644 --- a/libc/bionic/pthread_create.cpp +++ b/libc/bionic/pthread_create.cpp @@ -97,7 +97,6 @@ int _init_thread(pthread_internal_t* thread, bool add_to_thread_list) { } } - pthread_cond_init(&thread->join_cond, NULL); thread->cleanup_stack = NULL; if (add_to_thread_list) { @@ -215,17 +214,22 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, // the new thread. pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX]; pthread_mutex_init(start_mutex, NULL); - ScopedPthreadMutexLocker start_locker(start_mutex); + pthread_mutex_lock(start_mutex); thread->tls[TLS_SLOT_THREAD_ID] = thread; thread->start_routine = start_routine; thread->start_routine_arg = arg; - int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS; - int tid = __bionic_clone(flags, child_stack, NULL, thread->tls, NULL, __pthread_start, thread); - if (tid < 0) { + int flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM | + CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID; + int rc = __bionic_clone(flags, child_stack, &(thread->tid), thread->tls, &(thread->tid), __pthread_start, thread); + if (rc == -1) { int clone_errno = errno; + // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to + // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a + // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker. + pthread_mutex_unlock(start_mutex); if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) { munmap(thread->attr.stack_base, thread->attr.stack_size); } @@ -234,12 +238,10 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, return clone_errno; } - thread->tid = tid; - int init_errno = _init_thread(thread, true); if (init_errno != 0) { - // Mark the thread detached and let its __pthread_start run to - // completion. (It'll just exit immediately, cleaning up its resources.) + // Mark the thread detached and let its __pthread_start run to completion. + // It'll check this flag and exit immediately, cleaning up its resources. thread->internal_flags |= PTHREAD_INTERNAL_FLAG_THREAD_INIT_FAILED; thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED; return init_errno; @@ -251,8 +253,9 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr, _thread_created_hook(thread->tid); } - // Publish the pthread_t and let the thread run. - *thread_out = (pthread_t) thread; + // Publish the pthread_t and unlock the mutex to let the new thread start running. + *thread_out = reinterpret_cast<pthread_t>(thread); + pthread_mutex_unlock(start_mutex); return 0; } diff --git a/libc/bionic/pthread_exit.cpp b/libc/bionic/pthread_exit.cpp index cc86271..22c2c3c 100644 --- a/libc/bionic/pthread_exit.cpp +++ b/libc/bionic/pthread_exit.cpp @@ -57,8 +57,9 @@ void __pthread_cleanup_pop(__pthread_cleanup_t* c, int execute) { } } -void pthread_exit(void* retval) { +void pthread_exit(void* return_value) { pthread_internal_t* thread = __get_thread(); + thread->return_value = return_value; // Call the cleanup handlers first. while (thread->cleanup_stack) { @@ -90,10 +91,9 @@ void pthread_exit(void* retval) { size_t stack_size = thread->attr.stack_size; bool user_allocated_stack = ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) != 0); - // If the thread is detached, destroy the pthread_internal_t, - // otherwise keep it in memory and signal any joiners. pthread_mutex_lock(&gThreadListLock); - if (thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) { + if ((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) != 0) { + // The thread is detached, so we can destroy the pthread_internal_t. _pthread_internal_remove_locked(thread); } else { // Make sure that the pthread_internal_t doesn't have stale pointers to a stack that @@ -103,15 +103,8 @@ void pthread_exit(void* retval) { thread->attr.stack_size = 0; thread->tls = NULL; } - - // Indicate that the thread has exited for joining threads. - thread->attr.flags |= PTHREAD_ATTR_FLAG_ZOMBIE; - thread->return_value = retval; - - // Signal the joining thread if present. - if (thread->attr.flags & PTHREAD_ATTR_FLAG_JOINED) { - pthread_cond_signal(&thread->join_cond); - } + // pthread_join is responsible for destroying the pthread_internal_t for non-detached threads. + // The kernel will futex_wake on the pthread_internal_t::tid field to wake pthread_join. } pthread_mutex_unlock(&gThreadListLock); @@ -131,6 +124,6 @@ void pthread_exit(void* retval) { _exit_with_stack_teardown(stack_base, stack_size, 0); } - /* NOTREACHED, but we told the compiler this function is noreturn, and it doesn't believe us. */ + // NOTREACHED, but we told the compiler this function is noreturn, and it doesn't believe us. abort(); } diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h index d8ad544..de1ef26 100644 --- a/libc/bionic/pthread_internal.h +++ b/libc/bionic/pthread_internal.h @@ -31,28 +31,31 @@ #include <pthread.h> struct pthread_internal_t { - struct pthread_internal_t* next; - struct pthread_internal_t* prev; - pthread_attr_t attr; - pid_t tid; - bool allocated_on_heap; - pthread_cond_t join_cond; - void* return_value; - int internal_flags; - __pthread_cleanup_t* cleanup_stack; - void** tls; /* thread-local storage area */ - - void* (*start_routine)(void*); - void* start_routine_arg; - - void* alternate_signal_stack; - - /* - * The dynamic linker implements dlerror(3), which makes it hard for us to implement this - * per-thread buffer by simply using malloc(3) and free(3). - */ + struct pthread_internal_t* next; + struct pthread_internal_t* prev; + + pid_t tid; + + void** tls; + + pthread_attr_t attr; + bool allocated_on_heap; /* TODO: move this into attr.flags? */ + int internal_flags; /* TODO: move this into attr.flags? */ + + __pthread_cleanup_t* cleanup_stack; + + void* (*start_routine)(void*); + void* start_routine_arg; + void* return_value; + + void* alternate_signal_stack; + + /* + * The dynamic linker implements dlerror(3), which makes it hard for us to implement this + * per-thread buffer by simply using malloc(3) and free(3). + */ #define __BIONIC_DLERROR_BUFFER_SIZE 512 - char dlerror_buffer[__BIONIC_DLERROR_BUFFER_SIZE]; + char dlerror_buffer[__BIONIC_DLERROR_BUFFER_SIZE]; }; __LIBC_HIDDEN__ int _init_thread(pthread_internal_t* thread, bool add_to_thread_list); @@ -73,9 +76,6 @@ __LIBC_HIDDEN__ void _pthread_internal_remove_locked(pthread_internal_t* thread) /* Has the thread been joined by another thread? */ #define PTHREAD_ATTR_FLAG_JOINED 0x00000004 -/* Has the thread already exited but not been joined? */ -#define PTHREAD_ATTR_FLAG_ZOMBIE 0x00000008 - #define PTHREAD_INTERNAL_FLAG_THREAD_INIT_FAILED 1 /* diff --git a/libc/bionic/pthread_join.cpp b/libc/bionic/pthread_join.cpp index 7e022c2..0cbed62 100644 --- a/libc/bionic/pthread_join.cpp +++ b/libc/bionic/pthread_join.cpp @@ -28,33 +28,50 @@ #include <errno.h> +#include "private/bionic_futex.h" #include "pthread_accessor.h" -int pthread_join(pthread_t t, void** ret_val) { +int pthread_join(pthread_t t, void** return_value) { if (t == pthread_self()) { return EDEADLK; } - pthread_accessor thread(t); - if (thread.get() == NULL) { + pid_t tid; + volatile int* tid_ptr; + { + pthread_accessor thread(t); + if (thread.get() == NULL) { return ESRCH; - } + } - if (thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) { - return EINVAL; - } + if ((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) != 0) { + return EINVAL; + } + + if ((thread->attr.flags & PTHREAD_ATTR_FLAG_JOINED) != 0) { + return EINVAL; + } - if (thread->attr.flags & PTHREAD_ATTR_FLAG_JOINED) { - return EINVAL; + // Okay, looks like we can signal our intention to join. + thread->attr.flags |= PTHREAD_ATTR_FLAG_JOINED; + tid = thread->tid; + tid_ptr = &thread->tid; } - // Signal our intention to join, and wait for the thread to exit. - thread->attr.flags |= PTHREAD_ATTR_FLAG_JOINED; - while ((thread->attr.flags & PTHREAD_ATTR_FLAG_ZOMBIE) == 0) { - pthread_cond_wait(&thread->join_cond, &gThreadListLock); + // We set the PTHREAD_ATTR_FLAG_JOINED flag with the lock held, + // so no one is going to remove this thread except us. + + // Wait for the thread to actually exit, if it hasn't already. + while (*tid_ptr != 0) { + __futex_wait(tid_ptr, tid, NULL); } - if (ret_val) { - *ret_val = thread->return_value; + + // Take the lock again so we can pull the thread's return value + // and remove the thread from the list. + pthread_accessor thread(t); + + if (return_value) { + *return_value = thread->return_value; } _pthread_internal_remove_locked(thread.get()); diff --git a/libc/bionic/pthread_key.cpp b/libc/bionic/pthread_key.cpp index f2f4d20..6cc68af 100644 --- a/libc/bionic/pthread_key.cpp +++ b/libc/bionic/pthread_key.cpp @@ -218,7 +218,7 @@ int pthread_key_delete(pthread_key_t key) { // startup trampoline (__pthread_start) hasn't been run yet by the // scheduler. t->tls will also be NULL after a thread's stack has been // unmapped but before the ongoing pthread_join() is finished. - if ((t->attr.flags & PTHREAD_ATTR_FLAG_ZOMBIE) || t->tls == NULL) { + if (t->tid == 0 || t->tls == NULL) { continue; } diff --git a/libc/private/bionic_futex.h b/libc/private/bionic_futex.h index bfc3520..5602af7 100644 --- a/libc/private/bionic_futex.h +++ b/libc/private/bionic_futex.h @@ -28,6 +28,7 @@ #ifndef _BIONIC_FUTEX_H #define _BIONIC_FUTEX_H +#include <linux/compiler.h> /* needed for __user in non-uapi futex.h */ #include <linux/futex.h> #include <sys/cdefs.h> diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h index 094c71c..ff13fdb 100644 --- a/libc/private/bionic_tls.h +++ b/libc/private/bionic_tls.h @@ -51,7 +51,9 @@ enum { TLS_SLOT_THREAD_ID, TLS_SLOT_ERRNO, - /* This slot is used when starting a new thread, before any code that needs errno runs. */ + /* This slot in the child's TLS is used to synchronize the parent and child + * during thread initialization. The child finishes with this mutex before + * running any code that can set errno, so we can reuse the errno slot. */ TLS_SLOT_START_MUTEX = TLS_SLOT_ERRNO, /* These two aren't used by bionic itself, but allow the graphics code to |