third_party/musl/src/thread/pthread_create.c - cobalt - Git at Google

 #define _GNU_SOURCE
 #include "pthread_impl.h"
 #include "stdio_impl.h"
 #include "libc.h"
 #include <sys/mman.h>
 #include <string.h>
 #include <stddef.h>

 void *__mmap(void *, size_t, int, int, int, off_t);
 int __munmap(void *, size_t);
 int __mprotect(void *, size_t, int);

 static void dummy_0()
 {
 }
 weak_alias(dummy_0, __acquire_ptc);
 weak_alias(dummy_0, __release_ptc);
 weak_alias(dummy_0, __pthread_tsd_run_dtors);
 weak_alias(dummy_0, __do_orphaned_stdio_locks);
 weak_alias(dummy_0, __dl_thread_cleanup);

 static void *dummy_1(void *p)
 {
 	return 0;
 }
 weak_alias(dummy_1, __start_sched);

 _Noreturn void __pthread_exit(void *result)
 {
 	pthread_t self = __pthread_self();
 	sigset_t set;

 	self->canceldisable = 1;
 	self->cancelasync = 0;
 	self->result = result;

 	while (self->cancelbuf) {
 		void (*f)(void *) = self->cancelbuf->__f;
 		void *x = self->cancelbuf->__x;
 		self->cancelbuf = self->cancelbuf->__next;
 		f(x);
 	}

 	__pthread_tsd_run_dtors();

 	/* Access to target the exiting thread with syscalls that use
 	 * its kernel tid is controlled by killlock. For detached threads,
 	 * any use past this point would have undefined behavior, but for
 	 * joinable threads it's a valid usage that must be handled. */
 	LOCK(self->killlock);

 	/* Block all signals before decrementing the live thread count.
 	 * This is important to ensure that dynamically allocated TLS
 	 * is not under-allocated/over-committed, and possibly for other
 	 * reasons as well. */
 	__block_all_sigs(&set);

 	/* It's impossible to determine whether this is "the last thread"
 	 * until performing the atomic decrement, since multiple threads
 	 * could exit at the same time. For the last thread, revert the
 	 * decrement, restore the tid, and unblock signals to give the
 	 * atexit handlers and stdio cleanup code a consistent state. */
 	if (a_fetch_add(&libc.threads_minus_1, -1)==0) {
 		libc.threads_minus_1 = 0;
 		UNLOCK(self->killlock);
 		__restore_sigs(&set);
 		exit(0);
 	}

 	/* Process robust list in userspace to handle non-pshared mutexes
 	 * and the detached thread case where the robust list head will
 	 * be invalid when the kernel would process it. */
 	__vm_lock();
 	volatile void *volatile *rp;
 	while ((rp=self->robust_list.head) && rp != &self->robust_list.head) {
 		pthread_mutex_t *m = (void *)((char *)rp
 			- offsetof(pthread_mutex_t, _m_next));
 		int waiters = m->_m_waiters;
 		int priv = (m->_m_type & 128) ^ 128;
 		self->robust_list.pending = rp;
 		self->robust_list.head = *rp;
 		int cont = a_swap(&m->_m_lock, 0x40000000);
 		self->robust_list.pending = 0;
 		if (cont < 0 || waiters)
 			__wake(&m->_m_lock, 1, priv);
 	}
 	__vm_unlock();

 	__do_orphaned_stdio_locks();
 	__dl_thread_cleanup();

 	/* This atomic potentially competes with a concurrent pthread_detach
 	 * call; the loser is responsible for freeing thread resources. */
 	int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING);

 	if (state>=DT_DETACHED && self->map_base) {
 		/* Detached threads must avoid the kernel clear_child_tid
 		 * feature, since the virtual address will have been
 		 * unmapped and possibly already reused by a new mapping
 		 * at the time the kernel would perform the write. In
 		 * the case of threads that started out detached, the
 		 * initial clone flags are correct, but if the thread was
 		 * detached later, we need to clear it here. */
 		if (state == DT_DYNAMIC) __syscall(SYS_set_tid_address, 0);

 		/* Robust list will no longer be valid, and was already
 		 * processed above, so unregister it with the kernel. */
 		if (self->robust_list.off)
 			__syscall(SYS_set_robust_list, 0, 3*sizeof(long));

 		/* Since __unmapself bypasses the normal munmap code path,
 		 * explicitly wait for vmlock holders first. */
 		__vm_wait();

 		/* The following call unmaps the thread's stack mapping
 		 * and then exits without touching the stack. */
 		__unmapself(self->map_base, self->map_size);
 	}

 	/* After the kernel thread exits, its tid may be reused. Clear it
 	 * to prevent inadvertent use and inform functions that would use
 	 * it that it's no longer available. */
 	self->tid = 0;
 	UNLOCK(self->killlock);

 	for (;;) __syscall(SYS_exit, 0);
 }

 void __do_cleanup_push(struct __ptcb *cb)
 {
 	struct pthread *self = __pthread_self();
 	cb->__next = self->cancelbuf;
 	self->cancelbuf = cb;
 }

 void __do_cleanup_pop(struct __ptcb *cb)
 {
 	__pthread_self()->cancelbuf = cb->__next;
 }

 static int start(void *p)
 {
 	pthread_t self = p;
 	if (self->unblock_cancel)
 		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
 			SIGPT_SET, 0, _NSIG/8);
 	__pthread_exit(self->start(self->start_arg));
 	return 0;
 }

 static int start_c11(void *p)
 {
 	pthread_t self = p;
 	int (*start)(void*) = (int(*)(void*)) self->start;
 	__pthread_exit((void *)(uintptr_t)start(self->start_arg));
 	return 0;
 }

 #define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)

 /* pthread_key_create.c overrides this */
 static volatile size_t dummy = 0;
 weak_alias(dummy, __pthread_tsd_size);
 static void *dummy_tsd[1] = { 0 };
 weak_alias(dummy_tsd, __pthread_tsd_main);

 volatile int __block_new_threads = 0;
 extern size_t __default_stacksize;
 extern size_t __default_guardsize;

 static FILE *volatile dummy_file = 0;
 weak_alias(dummy_file, __stdin_used);
 weak_alias(dummy_file, __stdout_used);
 weak_alias(dummy_file, __stderr_used);

 static void init_file_lock(FILE *f)
 {
 	if (f && f->lock<0) f->lock = 0;
 }

 void *__copy_tls(unsigned char *);

 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
 {
 	int ret, c11 = (attrp == __ATTRP_C11_THREAD);
 	size_t size, guard;
 	struct pthread *self, *new;
 	unsigned char *map = 0, *stack = 0, *tsd = 0, *stack_limit;
 	unsigned flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND
 		| CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS
 		| CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED;
 	int do_sched = 0;
 	pthread_attr_t attr = { 0 };
 	struct start_sched_args ssa;

 	if (!libc.can_do_threads) return ENOSYS;
 	self = __pthread_self();
 	if (!libc.threaded) {
 		for (FILE *f=*__ofl_lock(); f; f=f->next)
 			init_file_lock(f);
 		__ofl_unlock();
 		init_file_lock(__stdin_used);
 		init_file_lock(__stdout_used);
 		init_file_lock(__stderr_used);
 		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
 		self->tsd = (void **)__pthread_tsd_main;
 		libc.threaded = 1;
 	}
 	if (attrp && !c11) attr = *attrp;

 	__acquire_ptc();
 	if (!attrp || c11) {
 		attr._a_stacksize = __default_stacksize;
 		attr._a_guardsize = __default_guardsize;
 	}

 	if (__block_new_threads) __wait(&__block_new_threads, 0, 1, 1);

 	if (attr._a_stackaddr) {
 		size_t need = libc.tls_size + __pthread_tsd_size;
 		size = attr._a_stacksize;
 		stack = (void *)(attr._a_stackaddr & -16);
 		stack_limit = (void *)(attr._a_stackaddr - size);
 		/* Use application-provided stack for TLS only when
 		 * it does not take more than ~12% or 2k of the
 		 * application's stack space. */
 		if (need < size/8 && need < 2048) {
 			tsd = stack - __pthread_tsd_size;
 			stack = tsd - libc.tls_size;
 			memset(stack, 0, need);
 		} else {
 			size = ROUND(need);
 		}
 		guard = 0;
 	} else {
 		guard = ROUND(attr._a_guardsize);
 		size = guard + ROUND(attr._a_stacksize
 			+ libc.tls_size +  __pthread_tsd_size);
 	}

 	if (!tsd) {
 		if (guard) {
 			map = __mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0);
 			if (map == MAP_FAILED) goto fail;
 			if (__mprotect(map+guard, size-guard, PROT_READ|PROT_WRITE)
 			    && errno != ENOSYS) {
 				__munmap(map, size);
 				goto fail;
 			}
 		} else {
 			map = __mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
 			if (map == MAP_FAILED) goto fail;
 		}
 		tsd = map + size - __pthread_tsd_size;
 		if (!stack) {
 			stack = tsd - libc.tls_size;
 			stack_limit = map + guard;
 		}
 	}

 	new = __copy_tls(tsd - libc.tls_size);
 	new->map_base = map;
 	new->map_size = size;
 	new->stack = stack;
 	new->stack_size = stack - stack_limit;
 	new->guard_size = guard;
 	new->start = entry;
 	new->start_arg = arg;
 	new->self = new;
 	new->tsd = (void *)tsd;
 	new->locale = &libc.global_locale;
 	if (attr._a_detach) {
 		new->detach_state = DT_DETACHED;
 		flags -= CLONE_CHILD_CLEARTID;
 	} else {
 		new->detach_state = DT_JOINABLE;
 	}
 	if (attr._a_sched) {
 		do_sched = 1;
 		ssa.futex = -1;
 		ssa.start_fn = new->start;
 		ssa.start_arg = new->start_arg;
 		ssa.attr = &attr;
 		new->start = __start_sched;
 		new->start_arg = &ssa;
 		__block_app_sigs(&ssa.mask);
 	}
 	new->robust_list.head = &new->robust_list.head;
 	new->unblock_cancel = self->cancel;
 	new->CANARY = self->CANARY;

 	a_inc(&libc.threads_minus_1);
 	ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->detach_state);

 	__release_ptc();

 	if (do_sched) {
 		__restore_sigs(&ssa.mask);
 	}

 	if (ret < 0) {
 		a_dec(&libc.threads_minus_1);
 		if (map) __munmap(map, size);
 		return EAGAIN;
 	}

 	if (do_sched) {
 		__futexwait(&ssa.futex, -1, 1);
 		ret = ssa.futex;
 		if (ret) return ret;
 	}

 	*res = new;
 	return 0;
 fail:
 	__release_ptc();
 	return EAGAIN;
 }

 weak_alias(__pthread_exit, pthread_exit);
 weak_alias(__pthread_create, pthread_create);
	#define _GNU_SOURCE
	#include "pthread_impl.h"
	#include "stdio_impl.h"
	#include "libc.h"
	#include <sys/mman.h>
	#include <string.h>
	#include <stddef.h>

	void __mmap(void , size_t, int, int, int, off_t);
	int __munmap(void *, size_t);
	int __mprotect(void *, size_t, int);

	static void dummy_0()
	{
	}
	weak_alias(dummy_0, __acquire_ptc);
	weak_alias(dummy_0, __release_ptc);
	weak_alias(dummy_0, __pthread_tsd_run_dtors);
	weak_alias(dummy_0, __do_orphaned_stdio_locks);
	weak_alias(dummy_0, __dl_thread_cleanup);

	static void dummy_1(void p)
	{
	return 0;
	}
	weak_alias(dummy_1, __start_sched);

	_Noreturn void __pthread_exit(void *result)
	{
	pthread_t self = __pthread_self();
	sigset_t set;

	self->canceldisable = 1;
	self->cancelasync = 0;
	self->result = result;

	while (self->cancelbuf) {
	void (f)(void ) = self->cancelbuf->__f;
	void *x = self->cancelbuf->__x;
	self->cancelbuf = self->cancelbuf->__next;
	f(x);
	}

	__pthread_tsd_run_dtors();

	/* Access to target the exiting thread with syscalls that use
	* its kernel tid is controlled by killlock. For detached threads,
	* any use past this point would have undefined behavior, but for
	* joinable threads it's a valid usage that must be handled. */
	LOCK(self->killlock);

	/* Block all signals before decrementing the live thread count.
	* This is important to ensure that dynamically allocated TLS
	* is not under-allocated/over-committed, and possibly for other
	* reasons as well. */
	__block_all_sigs(&set);

	/* It's impossible to determine whether this is "the last thread"
	* until performing the atomic decrement, since multiple threads
	* could exit at the same time. For the last thread, revert the
	* decrement, restore the tid, and unblock signals to give the
	* atexit handlers and stdio cleanup code a consistent state. */
	if (a_fetch_add(&libc.threads_minus_1, -1)==0) {
	libc.threads_minus_1 = 0;
	UNLOCK(self->killlock);
	__restore_sigs(&set);
	exit(0);
	}

	/* Process robust list in userspace to handle non-pshared mutexes
	* and the detached thread case where the robust list head will
	* be invalid when the kernel would process it. */
	__vm_lock();
	volatile void volatile rp;
	while ((rp=self->robust_list.head) && rp != &self->robust_list.head) {
	pthread_mutex_t m = (void )((char *)rp
	- offsetof(pthread_mutex_t, _m_next));
	int waiters = m->_m_waiters;
	int priv = (m->_m_type & 128) ^ 128;
	self->robust_list.pending = rp;
	self->robust_list.head = *rp;
	int cont = a_swap(&m->_m_lock, 0x40000000);
	self->robust_list.pending = 0;
	if (cont < 0 \|\| waiters)
	__wake(&m->_m_lock, 1, priv);
	}
	__vm_unlock();

	__do_orphaned_stdio_locks();
	__dl_thread_cleanup();

	/* This atomic potentially competes with a concurrent pthread_detach
	* call; the loser is responsible for freeing thread resources. */
	int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING);

	if (state>=DT_DETACHED && self->map_base) {
	/* Detached threads must avoid the kernel clear_child_tid
	* feature, since the virtual address will have been
	* unmapped and possibly already reused by a new mapping
	* at the time the kernel would perform the write. In
	* the case of threads that started out detached, the
	* initial clone flags are correct, but if the thread was
	* detached later, we need to clear it here. */
	if (state == DT_DYNAMIC) __syscall(SYS_set_tid_address, 0);

	/* Robust list will no longer be valid, and was already
	* processed above, so unregister it with the kernel. */
	if (self->robust_list.off)
	__syscall(SYS_set_robust_list, 0, 3*sizeof(long));

	/* Since __unmapself bypasses the normal munmap code path,
	* explicitly wait for vmlock holders first. */
	__vm_wait();

	/* The following call unmaps the thread's stack mapping
	* and then exits without touching the stack. */
	__unmapself(self->map_base, self->map_size);
	}

	/* After the kernel thread exits, its tid may be reused. Clear it
	* to prevent inadvertent use and inform functions that would use
	* it that it's no longer available. */
	self->tid = 0;
	UNLOCK(self->killlock);

	for (;;) __syscall(SYS_exit, 0);
	}

	void __do_cleanup_push(struct __ptcb *cb)
	{
	struct pthread *self = __pthread_self();
	cb->__next = self->cancelbuf;
	self->cancelbuf = cb;
	}

	void __do_cleanup_pop(struct __ptcb *cb)
	{
	__pthread_self()->cancelbuf = cb->__next;
	}

	static int start(void *p)
	{
	pthread_t self = p;
	if (self->unblock_cancel)
	__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
	SIGPT_SET, 0, _NSIG/8);
	__pthread_exit(self->start(self->start_arg));
	return 0;
	}

	static int start_c11(void *p)
	{
	pthread_t self = p;
	int (start)(void) = (int()(void)) self->start;
	__pthread_exit((void *)(uintptr_t)start(self->start_arg));
	return 0;
	}

	#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)

	/* pthread_key_create.c overrides this */
	static volatile size_t dummy = 0;
	weak_alias(dummy, __pthread_tsd_size);
	static void *dummy_tsd[1] = { 0 };
	weak_alias(dummy_tsd, __pthread_tsd_main);

	volatile int __block_new_threads = 0;
	extern size_t __default_stacksize;
	extern size_t __default_guardsize;

	static FILE *volatile dummy_file = 0;
	weak_alias(dummy_file, __stdin_used);
	weak_alias(dummy_file, __stdout_used);
	weak_alias(dummy_file, __stderr_used);

	static void init_file_lock(FILE *f)
	{
	if (f && f->lock<0) f->lock = 0;
	}

	void __copy_tls(unsigned char );

	int __pthread_create(pthread_t restrict res, const pthread_attr_t restrict attrp, void (entry)(void ), void restrict arg)
	{
	int ret, c11 = (attrp == __ATTRP_C11_THREAD);
	size_t size, guard;
	struct pthread self, new;
	unsigned char map = 0, stack = 0, tsd = 0, stack_limit;
	unsigned flags = CLONE_VM \| CLONE_FS \| CLONE_FILES \| CLONE_SIGHAND
	\| CLONE_THREAD \| CLONE_SYSVSEM \| CLONE_SETTLS
	\| CLONE_PARENT_SETTID \| CLONE_CHILD_CLEARTID \| CLONE_DETACHED;
	int do_sched = 0;
	pthread_attr_t attr = { 0 };
	struct start_sched_args ssa;

	if (!libc.can_do_threads) return ENOSYS;
	self = __pthread_self();
	if (!libc.threaded) {
	for (FILE f=__ofl_lock(); f; f=f->next)
	init_file_lock(f);
	__ofl_unlock();
	init_file_lock(__stdin_used);
	init_file_lock(__stdout_used);
	init_file_lock(__stderr_used);
	__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
	self->tsd = (void **)__pthread_tsd_main;
	libc.threaded = 1;
	}
	if (attrp && !c11) attr = *attrp;

	__acquire_ptc();
	if (!attrp \|\| c11) {
	attr._a_stacksize = __default_stacksize;
	attr._a_guardsize = __default_guardsize;
	}

	if (__block_new_threads) __wait(&__block_new_threads, 0, 1, 1);

	if (attr._a_stackaddr) {
	size_t need = libc.tls_size + __pthread_tsd_size;
	size = attr._a_stacksize;
	stack = (void *)(attr._a_stackaddr & -16);
	stack_limit = (void *)(attr._a_stackaddr - size);
	/* Use application-provided stack for TLS only when
	* it does not take more than ~12% or 2k of the
	* application's stack space. */
	if (need < size/8 && need < 2048) {
	tsd = stack - __pthread_tsd_size;
	stack = tsd - libc.tls_size;
	memset(stack, 0, need);
	} else {
	size = ROUND(need);
	}
	guard = 0;
	} else {
	guard = ROUND(attr._a_guardsize);
	size = guard + ROUND(attr._a_stacksize
	+ libc.tls_size + __pthread_tsd_size);
	}

	if (!tsd) {
	if (guard) {
	map = __mmap(0, size, PROT_NONE, MAP_PRIVATE\|MAP_ANON, -1, 0);
	if (map == MAP_FAILED) goto fail;
	if (__mprotect(map+guard, size-guard, PROT_READ\|PROT_WRITE)
	&& errno != ENOSYS) {
	__munmap(map, size);
	goto fail;
	}
	} else {
	map = __mmap(0, size, PROT_READ\|PROT_WRITE, MAP_PRIVATE\|MAP_ANON, -1, 0);
	if (map == MAP_FAILED) goto fail;
	}
	tsd = map + size - __pthread_tsd_size;
	if (!stack) {
	stack = tsd - libc.tls_size;
	stack_limit = map + guard;
	}
	}

	new = __copy_tls(tsd - libc.tls_size);
	new->map_base = map;
	new->map_size = size;
	new->stack = stack;
	new->stack_size = stack - stack_limit;
	new->guard_size = guard;
	new->start = entry;
	new->start_arg = arg;
	new->self = new;
	new->tsd = (void *)tsd;
	new->locale = &libc.global_locale;
	if (attr._a_detach) {
	new->detach_state = DT_DETACHED;
	flags -= CLONE_CHILD_CLEARTID;
	} else {
	new->detach_state = DT_JOINABLE;
	}
	if (attr._a_sched) {
	do_sched = 1;
	ssa.futex = -1;
	ssa.start_fn = new->start;
	ssa.start_arg = new->start_arg;
	ssa.attr = &attr;
	new->start = __start_sched;
	new->start_arg = &ssa;
	__block_app_sigs(&ssa.mask);
	}
	new->robust_list.head = &new->robust_list.head;
	new->unblock_cancel = self->cancel;
	new->CANARY = self->CANARY;

	a_inc(&libc.threads_minus_1);
	ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->detach_state);

	__release_ptc();

	if (do_sched) {
	__restore_sigs(&ssa.mask);
	}

	if (ret < 0) {
	a_dec(&libc.threads_minus_1);
	if (map) __munmap(map, size);
	return EAGAIN;
	}

	if (do_sched) {
	__futexwait(&ssa.futex, -1, 1);
	ret = ssa.futex;
	if (ret) return ret;
	}

	*res = new;
	return 0;
	fail:
	__release_ptc();
	return EAGAIN;
	}

	weak_alias(__pthread_exit, pthread_exit);
	weak_alias(__pthread_create, pthread_create);