| #include <sys/membarrier.h> |
| #include <semaphore.h> |
| #include <signal.h> |
| #include <string.h> |
| #include "pthread_impl.h" |
| #include "syscall.h" |
| |
| static void dummy_0(void) |
| { |
| } |
| |
| weak_alias(dummy_0, __tl_lock); |
| weak_alias(dummy_0, __tl_unlock); |
| |
| static sem_t barrier_sem; |
| |
| static void bcast_barrier(int s) |
| { |
| sem_post(&barrier_sem); |
| } |
| |
| int __membarrier(int cmd, int flags) |
| { |
| int r = __syscall(SYS_membarrier, cmd, flags); |
| /* Emulate the private expedited command, which is needed by the |
| * dynamic linker for installation of dynamic TLS, for older |
| * kernels that lack the syscall. Unlike the syscall, this only |
| * synchronizes with threads of the process, not other processes |
| * sharing the VM, but such sharing is not a supported usage |
| * anyway. */ |
| if (r && cmd == MEMBARRIER_CMD_PRIVATE_EXPEDITED && !flags) { |
| pthread_t self=__pthread_self(), td; |
| sigset_t set; |
| __block_app_sigs(&set); |
| __tl_lock(); |
| sem_init(&barrier_sem, 0, 0); |
| struct sigaction sa = { |
| .sa_flags = SA_RESTART, |
| .sa_handler = bcast_barrier |
| }; |
| memset(&sa.sa_mask, -1, sizeof sa.sa_mask); |
| if (!__libc_sigaction(SIGSYNCCALL, &sa, 0)) { |
| for (td=self->next; td!=self; td=td->next) |
| __syscall(SYS_tkill, td->tid, SIGSYNCCALL); |
| for (td=self->next; td!=self; td=td->next) |
| sem_wait(&barrier_sem); |
| r = 0; |
| sa.sa_handler = SIG_IGN; |
| __libc_sigaction(SIGSYNCCALL, &sa, 0); |
| } |
| sem_destroy(&barrier_sem); |
| __tl_unlock(); |
| __restore_sigs(&set); |
| } |
| return __syscall_ret(r); |
| } |
| |
| void __membarrier_init(void) |
| { |
| /* If membarrier is linked, attempt to pre-register to be able to use |
| * the private expedited command before the process becomes multi- |
| * threaded, since registering later has bad, potentially unbounded |
| * latency. This syscall should be essentially free, and it's arguably |
| * a mistake in the API design that registration was even required. |
| * For other commands, registration may impose some cost, so it's left |
| * to the application to do so if desired. Unfortunately this means |
| * library code initialized after the process becomes multi-threaded |
| * cannot use these features without accepting registration latency. */ |
| __syscall(SYS_membarrier, MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0); |
| } |
| |
| weak_alias(__membarrier, membarrier); |