[wasi-libc.git] / libc-top-half / musl / src / thread / pthread_create.c

#define _GNU_SOURCE
#include "pthread_impl.h"
#include "stdio_impl.h"
#include "libc.h"
#include "lock.h"
#ifdef __wasilibc_unmodified_upstream
#include <sys/mman.h>
#endif
#include <string.h>
#include <stddef.h>
#ifndef __wasilibc_unmodified_upstream
#include <stdatomic.h>
#endif

#include <stdalign.h>

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);
#ifdef __wasilibc_unmodified_upstream
weak_alias(dummy_0, __dl_thread_cleanup);
weak_alias(dummy_0, __membarrier_init);
#endif

static int tl_lock_count;
static int tl_lock_waiters;

void __tl_lock(void)
{
        int tid = __pthread_self()->tid;
        int val = __thread_list_lock;
        if (val == tid) {
                tl_lock_count++;
                return;
        }
        while ((val = a_cas(&__thread_list_lock, 0, tid)))
                __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
}

void __tl_unlock(void)
{
        if (tl_lock_count) {
                tl_lock_count--;
                return;
        }
        a_store(&__thread_list_lock, 0);
        if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
}

void __tl_sync(pthread_t td)
{
        a_barrier();
        int val = __thread_list_lock;
        if (!val) return;
        __wait(&__thread_list_lock, &tl_lock_waiters, val, 0);
        if (tl_lock_waiters) __wake(&__thread_list_lock, 1, 0);
}

#ifdef __wasilibc_unmodified_upstream
_Noreturn void __pthread_exit(void *result)
#else
static void __pthread_exit(void *result)
#endif
{
        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();

#ifdef __wasilibc_unmodified_upstream
        __block_app_sigs(&set);
#endif

        /* 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) {
                /* Since __unmapself bypasses the normal munmap code path,
                 * explicitly wait for vmlock holders first. This must be
                 * done before any locks are taken, to avoid lock ordering
                 * issues that could lead to deadlock. */
#ifdef __wasilibc_unmodified_upstream
                __vm_wait();
#endif
        }

        /* 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.
         * Signals must be blocked since pthread_kill must be AS-safe. */
        LOCK(self->killlock);

        /* The thread list lock must be AS-safe, and thus depends on
         * application signals being blocked above. */
        __tl_lock();

        /* If this is the only thread in the list, don't proceed with
         * termination of the thread, but restore the previous lock and
         * signal state to prepare for exit to call atexit handlers. */
        if (self->next == self) {
                __tl_unlock();
                UNLOCK(self->killlock);
                self->detach_state = state;
#ifdef __wasilibc_unmodified_upstream
                __restore_sigs(&set);
#endif
                exit(0);
        }

        /* At this point we are committed to thread termination. */

#ifdef __wasilibc_unmodified_upstream
        /* 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();
#endif
        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);
        }
#ifdef __wasilibc_unmodified_upstream
        __vm_unlock();
#endif

        __do_orphaned_stdio_locks();
#ifdef __wasilibc_unmodified_upstream
        __dl_thread_cleanup();
#endif

        /* Last, unlink thread from the list. This change will not be visible
         * until the lock is released, which only happens after SYS_exit
         * has been called, via the exit futex address pointing at the lock.
         * This needs to happen after any possible calls to LOCK() that might
         * skip locking if process appears single-threaded. */
        if (!--libc.threads_minus_1) libc.need_locks = -1;
        self->next->prev = self->prev;
        self->prev->next = self->next;
        self->prev = self->next = self;

#ifndef __wasilibc_unmodified_upstream
        /* On Linux, the thread is created with CLONE_CHILD_CLEARTID,
         * and this lock will unlock by kernel when this thread terminates.
         * So we should unlock it here in WebAssembly.
         * See also set_tid_address(2) */
        __tl_unlock();
#endif

#ifdef __wasilibc_unmodified_upstream
        if (state==DT_DETACHED && self->map_base) {
                /* Detached threads must block even implementation-internal
                 * signals, since they will not have a stack in their last
                 * moments of existence. */
                __block_all_sigs(&set);

                /* 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));

                /* The following call unmaps the thread's stack mapping
                 * and then exits without touching the stack. */
                __unmapself(self->map_base, self->map_size);
        }
#else
        if (state==DT_DETACHED && self->map_base) {
                // __syscall(SYS_exit) would unlock the thread, list
                // do it manually here
                __tl_unlock();
                free(self->map_base);
                // Can't use `exit()` here, because it is too high level
                return;
        }
#endif

        /* Wake any joiner. */
        a_store(&self->detach_state, DT_EXITED);
        __wake(&self->detach_state, 1, 1);

        /* 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);

#ifdef __wasilibc_unmodified_upstream
        for (;;) __syscall(SYS_exit, 0);
#else
        // __syscall(SYS_exit) would unlock the thread, list
        // do it manually here
        __tl_unlock();
        // Can't use `exit()` here, because it is too high level
#endif
}

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;
}

struct start_args {
#ifdef __wasilibc_unmodified_upstream
        void *(*start_func)(void *);
        void *start_arg;
        volatile int control;
        unsigned long sig_mask[_NSIG/8/sizeof(long)];
#else
        void *(*start_func)(void *);
        void *start_arg;
        void *tls_base;
#endif
};

#ifdef __wasilibc_unmodified_upstream
static int start(void *p)
{
        struct start_args *args = p;
        int state = args->control;
        if (state) {
                if (a_cas(&args->control, 1, 2)==1)
                        __wait(&args->control, 0, 2, 1);
                if (args->control) {
#ifdef __wasilibc_unmodified_upstream
                        __syscall(SYS_set_tid_address, &args->control);
                        for (;;) __syscall(SYS_exit, 0);
#endif
                }
        }
#ifdef __wasilibc_unmodified_upstream
        __syscall(SYS_rt_sigprocmask, SIG_SETMASK, &args->sig_mask, 0, _NSIG/8);
#endif
        __pthread_exit(args->start_func(args->start_arg));
        return 0;
}

static int start_c11(void *p)
{
        struct start_args *args = p;
        int (*start)(void*) = (int(*)(void*)) args->start_func;
        __pthread_exit((void *)(uintptr_t)start(args->start_arg));
        return 0;
}
#else
__attribute__((export_name("wasi_thread_start")))
void wasi_thread_start(int tid, void *p)
{
        /*
         * Note: it's fragile to implement wasi_thread_start in C.
         * On entry, we don't even have C stack (__stack_pointer)
         * set up. Be careful when modifying this function.
         */
        struct start_args *args = p;
        __asm__(".globaltype __tls_base, i32\n"
                        "local.get %0\n"
                        "global.set __tls_base\n"
                        :: "r"(args->tls_base));
        pthread_t self = __pthread_self();
        // Set the thread ID (TID) on the pthread structure. The TID is stored
        // atomically since it is also stored by the parent thread; this way,
        // whichever thread (parent or child) reaches this point first can proceed
        // without waiting.
        atomic_store((atomic_int *) &(self->tid), tid);
        // Set the stack pointer.
        __asm__(".globaltype __stack_pointer, i32\n"
                        "local.get %0\n"
                        "global.set __stack_pointer\n"
                        :: "r"(self->stack));
        // Execute the user's start function.
        __pthread_exit(args->start_func(args->start_arg));
}
#endif

#ifdef __wasilibc_unmodified_upstream
#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)
#else
/*
 * As we allocate stack with malloc() instead of mmap/mprotect,
 * there is no point to round it up to PAGE_SIZE.
 * Instead, round up to a sane alignment.
 * Note: PAGE_SIZE is rather big on WASM. (65536)
 */
#define ROUND(x) (((x)+16-1)&-16)
#endif

/* 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);

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;
}

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;
#ifdef __wasilibc_unmodified_upstream
        unsigned flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND
                | CLONE_THREAD | CLONE_SYSVSEM | CLONE_SETTLS
                | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED;
#endif
        pthread_attr_t attr = { 0 };
        sigset_t set;
#ifndef __wasilibc_unmodified_upstream
        size_t tls_size = __builtin_wasm_tls_size();
        size_t tls_align = __builtin_wasm_tls_align();
        void* tls_base = __builtin_wasm_tls_base();
        void* new_tls_base;
        size_t tls_offset;
        tls_size += tls_align;
#endif

#ifdef __wasilibc_unmodified_upstream
        if (!libc.can_do_threads) return ENOSYS;
#endif
        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);
#ifdef __wasilibc_unmodified_upstream
                __syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, _NSIG/8);
#endif
                self->tsd = (void **)__pthread_tsd_main;
#ifdef __wasilibc_unmodified_upstream
                __membarrier_init();
#endif
                libc.threaded = 1;
        }
        if (attrp && !c11) attr = *attrp;

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

        if (attr._a_stackaddr) {
#ifdef __wasilibc_unmodified_upstream
                size_t need = libc.tls_size + __pthread_tsd_size;
#else
                size_t need = tls_size + __pthread_tsd_size;
#endif
                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;
#ifdef __wasilibc_unmodified_upstream
                        stack = tsd - libc.tls_size;
#else
                        stack = tsd - tls_size;
#endif
                        memset(stack, 0, need);
                } else {
                        size = ROUND(need);
                }
                guard = 0;
        } else {
                guard = ROUND(attr._a_guardsize);
                size = guard + ROUND(attr._a_stacksize
#ifdef __wasilibc_unmodified_upstream
                        + libc.tls_size +  __pthread_tsd_size);
#else
                        + tls_size +  __pthread_tsd_size);
#endif
        }

        if (!tsd) {
#ifdef __wasilibc_unmodified_upstream
                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;
                }
#else
                map = malloc(size);
                if (!map) goto fail;
#endif
                tsd = map + size - __pthread_tsd_size;
                if (!stack) {
#ifdef __wasilibc_unmodified_upstream
                        stack = tsd - libc.tls_size;
#else
                        stack = tsd - tls_size;
#endif
                        stack_limit = map + guard;
                }
        }

#ifdef __wasilibc_unmodified_upstream
        new = __copy_tls(tsd - libc.tls_size);
#else
        new_tls_base = __copy_tls(tsd - tls_size);
        tls_offset = new_tls_base - tls_base;
        new = (void*)((uintptr_t)self + tls_offset);
#endif
        new->map_base = map;
        new->map_size = size;
        new->stack = stack;
        new->stack_size = stack - stack_limit;
        new->guard_size = guard;
        new->self = new;
        new->tsd = (void *)tsd;
        new->locale = &libc.global_locale;
        if (attr._a_detach) {
                new->detach_state = DT_DETACHED;
        } else {
                new->detach_state = DT_JOINABLE;
        }
        new->robust_list.head = &new->robust_list.head;
        new->canary = self->canary;
        new->sysinfo = self->sysinfo;

        /* Setup argument structure for the new thread on its stack.
         * It's safe to access from the caller only until the thread
         * list is unlocked. */
#ifdef __wasilibc_unmodified_upstream
        stack -= (uintptr_t)stack % sizeof(uintptr_t);
        stack -= sizeof(struct start_args);
        struct start_args *args = (void *)stack;
        args->start_func = entry;
        args->start_arg = arg;
        args->control = attr._a_sched ? 1 : 0;

        /* Application signals (but not the synccall signal) must be
         * blocked before the thread list lock can be taken, to ensure
         * that the lock is AS-safe. */
        __block_app_sigs(&set);

        /* Ensure SIGCANCEL is unblocked in new thread. This requires
         * working with a copy of the set so we can restore the
         * original mask in the calling thread. */
        memcpy(&args->sig_mask, &set, sizeof args->sig_mask);
        args->sig_mask[(SIGCANCEL-1)/8/sizeof(long)] &=
                ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
#else
        /* Align the stack to struct start_args */
        stack -= sizeof(struct start_args);
        stack -= (uintptr_t)stack % alignof(struct start_args);
        struct start_args *args = (void *)stack;

        /* Align the stack to 16 and store it */
        new->stack = (void *)((uintptr_t) stack & -16);
        /* Correct the stack size */
        new->stack_size = stack - stack_limit;

        args->start_func = entry;
        args->start_arg = arg;
        args->tls_base = (void*)new_tls_base;
#endif

        __tl_lock();
        if (!libc.threads_minus_1++) libc.need_locks = 1;
#ifdef __wasilibc_unmodified_upstream
        ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock);
#else
        /* Instead of `__clone`, WASI uses a host API to instantiate a new version
         * of the current module and start executing the entry function. The
         * wasi-threads specification requires the module to export a
         * `wasi_thread_start` function, which is invoked with `args`. */
        ret = __wasi_thread_spawn((void *) args);
#endif

#ifdef __wasilibc_unmodified_upstream
        /* All clone failures translate to EAGAIN. If explicit scheduling
         * was requested, attempt it before unlocking the thread list so
         * that the failed thread is never exposed and so that we can
         * clean up all transient resource usage before returning. */
        if (ret < 0) {
                ret = -EAGAIN;
        } else if (attr._a_sched) {
                ret = __syscall(SYS_sched_setscheduler,
                        new->tid, attr._a_policy, &attr._a_prio);
                if (a_swap(&args->control, ret ? 3 : 0)==2)
                        __wake(&args->control, 1, 1);
                if (ret)
                        __wait(&args->control, 0, 3, 0);
        }
#else
        /* `wasi_thread_spawn` will either return a host-provided thread ID (TID)
         * (`>= 0`) or an error code (`< 0`). As in the unmodified version, all
         * spawn failures translate to EAGAIN; unlike the modified version, there is
         * no need to "start up" the child thread--the host does this. If the spawn
         * did succeed, then we store the TID atomically, since this parent thread
         * is racing with the child thread to set this field; this way, whichever
         * thread reaches this point first can continue without waiting. */
        if (ret < 0) {
                ret = -EAGAIN;
        } else {
                atomic_store((atomic_int *) &(new->tid), ret);
        }
#endif

        if (ret >= 0) {
                new->next = self->next;
                new->prev = self;
                new->next->prev = new;
                new->prev->next = new;
        } else {
                if (!--libc.threads_minus_1) libc.need_locks = 0;
        }
        __tl_unlock();
#ifdef __wasilibc_unmodified_upstream
        __restore_sigs(&set);
#endif
        __release_ptc();

        if (ret < 0) {
#ifdef __wasilibc_unmodified_upstream
                if (map) __munmap(map, size);
#else
                free(map);
#endif
                return -ret;
        }

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

#ifdef __wasilibc_unmodified_upstream
weak_alias(__pthread_exit, pthread_exit);
#endif
weak_alias(__pthread_create, pthread_create);