diff options
Diffstat (limited to 'src/thread/pthread_create.c')
| -rw-r--r-- | src/thread/pthread_create.c | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c new file mode 100644 index 00000000..6fa484c7 --- /dev/null +++ b/src/thread/pthread_create.c @@ -0,0 +1,189 @@ +#include "pthread_impl.h" + +#define pthread_self __pthread_self + +static void docancel(struct pthread *self) +{ + struct __ptcb cb = { .__next = self->cancelbuf }; + __pthread_unwind_next(&cb); +} + +static void cancel_handler(int sig, siginfo_t *si, void *ctx) +{ + struct pthread *self = pthread_self(); + self->cancel = 1; + if (self->canceldisable || (!self->cancelasync && !self->cancelpoint)) + return; + docancel(self); +} + +/* "rsyscall" is a mechanism by which a thread can synchronously force all + * other threads to perform an arbitrary syscall. It is necessary to work + * around the non-conformant implementation of setuid() et al on Linux, + * which affect only the calling thread and not the whole process. This + * implementation performs some tricks with signal delivery to work around + * the fact that it does not keep any list of threads in userspace. */ + +static struct { + volatile int lock, hold, blocks, cnt; + unsigned long arg[6]; + int nr; + int err; +} rs; + +static void rsyscall_handler(int sig, siginfo_t *si, void *ctx) +{ + if (rs.cnt == libc.threads_minus_1) return; + + if (syscall6(rs.nr, rs.arg[0], rs.arg[1], rs.arg[2], + rs.arg[3], rs.arg[4], rs.arg[5]) < 0 && !rs.err) rs.err=errno; + + a_inc(&rs.cnt); + __wake(&rs.cnt, 1, 1); + while(rs.hold) + __wait(&rs.hold, 0, 1, 1); + a_dec(&rs.cnt); + if (!rs.cnt) __wake(&rs.cnt, 1, 1); +} + +static int rsyscall(int nr, long a, long b, long c, long d, long e, long f) +{ + int i, ret; + sigset_t set = { 0 }; + struct pthread *self = pthread_self(); + sigaddset(&set, SIGSYSCALL); + + LOCK(&rs.lock); + while ((i=rs.blocks)) + __wait(&rs.blocks, 0, i, 1); + + __libc_sigprocmask(SIG_BLOCK, &set, 0); + + rs.nr = nr; + rs.arg[0] = a; rs.arg[1] = b; + rs.arg[2] = c; rs.arg[3] = d; + rs.arg[4] = d; rs.arg[5] = f; + rs.hold = 1; + rs.err = 0; + rs.cnt = 0; + + /* Dispatch signals until all threads respond */ + for (i=libc.threads_minus_1; i; i--) + sigqueue(self->pid, SIGSYSCALL, (union sigval){0}); + while ((i=rs.cnt) < libc.threads_minus_1) { + sigqueue(self->pid, SIGSYSCALL, (union sigval){0}); + __wait(&rs.cnt, 0, i, 1); + } + + /* Handle any lingering signals with no-op */ + __libc_sigprocmask(SIG_UNBLOCK, &set, 0); + + /* Resume other threads' signal handlers and wait for them */ + rs.hold = 0; + __wake(&rs.hold, -1, 0); + while((i=rs.cnt)) __wait(&rs.cnt, 0, i, 1); + + if (rs.err) errno = rs.err, ret = -1; + else ret = syscall6(nr, a, b, c, d, e, f); + + UNLOCK(&rs.lock); + return ret; +} + +static void cancelpt(int x) +{ + struct pthread *self = pthread_self(); + if (self->canceldisable) return; + self->cancelpoint = x; + if (self->cancel) docancel(self); +} + +static void init_threads() +{ + struct sigaction sa = { .sa_flags = SA_SIGINFO | SA_RESTART }; + libc.lock = __lock; + libc.cancelpt = cancelpt; + libc.rsyscall = rsyscall; + sa.sa_sigaction = cancel_handler; + __libc_sigaction(SIGCANCEL, &sa, 0); + sigaddset(&sa.sa_mask, SIGSYSCALL); + sigaddset(&sa.sa_mask, SIGCANCEL); + sa.sa_sigaction = rsyscall_handler; + __libc_sigaction(SIGSYSCALL, &sa, 0); + sigprocmask(SIG_UNBLOCK, &sa.sa_mask, 0); +} + +static int start(void *p) +{ + struct pthread *self = p; + pthread_exit(self->start(self->start_arg)); + return 0; +} + +#undef pthread_self + +#define CLONE_MAGIC 0x7d0f00 +int __clone(int (*)(void *), void *, int, void *, pid_t *, void *, pid_t *); + +#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE) + +/* pthread_key_create.c overrides this */ +static const size_t dummy = 0; +weak_alias(dummy, __pthread_tsd_size); + +int pthread_create(pthread_t *res, const pthread_attr_t *attr, void *(*entry)(void *), void *arg) +{ + static int init; + int ret; + size_t size, guard; + struct pthread *self = pthread_self(), *new; + unsigned char *map, *stack, *tsd; + static const pthread_attr_t default_attr; + + if (!self) return errno = ENOSYS; + if (!init && ++init) init_threads(); + + if (!attr) attr = &default_attr; + guard = ROUND(attr->__guardsize + DEFAULT_GUARD_SIZE); + size = guard + ROUND(attr->__stacksize + DEFAULT_STACK_SIZE); + size += __pthread_tsd_size; + map = mmap(0, size, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0); + if (!map) return EAGAIN; + mprotect(map, guard, PROT_NONE); + + tsd = map + size - __pthread_tsd_size; + new = (void *)(tsd - sizeof *new - PAGE_SIZE%sizeof *new); + new->map_base = map; + new->map_size = size; + new->pid = self->pid; + new->errno_ptr = &new->errno_val; + new->start = entry; + new->start_arg = arg; + new->self = new; + new->tsd = (void *)tsd; + new->detached = attr->__detach; + new->attr = *attr; + memcpy(new->tlsdesc, self->tlsdesc, sizeof new->tlsdesc); + new->tlsdesc[1] = (uintptr_t)new; + stack = (void *)((uintptr_t)new-1 & ~(uintptr_t)15); + + /* We must synchronize new thread creation with rsyscall + * delivery. This looks to be the least expensive way: */ + a_inc(&rs.blocks); + while (rs.lock) __wait(&rs.lock, 0, 1, 1); + + a_inc(&libc.threads_minus_1); + ret = __clone(start, stack, CLONE_MAGIC, new, + &new->tid, &new->tlsdesc, &new->tid); + + a_dec(&rs.blocks); + if (rs.lock) __wake(&rs.blocks, 1, 1); + + if (ret < 0) { + a_dec(&libc.threads_minus_1); + munmap(map, size); + return -ret; + } + *res = new; + return 0; +} |