1 #include <sys/membarrier.h>
5 #include "pthread_impl.h"
8 static void dummy_0(void)
12 static void dummy_1(pthread_t t)
16 weak_alias(dummy_0, __tl_lock);
17 weak_alias(dummy_0, __tl_unlock);
18 weak_alias(dummy_1, __tl_sync);
20 static sem_t barrier_sem;
22 static void bcast_barrier(int s)
24 sem_post(&barrier_sem);
27 int __membarrier(int cmd, int flags)
29 int r = __syscall(SYS_membarrier, cmd, flags);
30 /* Emulate the private expedited command, which is needed by the
31 * dynamic linker for installation of dynamic TLS, for older
32 * kernels that lack the syscall. Unlike the syscall, this only
33 * synchronizes with threads of the process, not other processes
34 * sharing the VM, but such sharing is not a supported usage
36 if (r && cmd == MEMBARRIER_CMD_PRIVATE_EXPEDITED && !flags) {
37 pthread_t self=__pthread_self(), td;
39 __block_app_sigs(&set);
41 sem_init(&barrier_sem, 0, 0);
42 struct sigaction sa = {
43 .sa_flags = SA_RESTART,
44 .sa_handler = bcast_barrier
46 memset(&sa.sa_mask, -1, sizeof sa.sa_mask);
47 __libc_sigaction(SIGSYNCCALL, &sa, 0);
48 for (td=self->next; td!=self; td=td->next)
49 __syscall(SYS_tkill, td->tid, SIGSYNCCALL);
50 for (td=self->next; td!=self; td=td->next)
51 sem_wait(&barrier_sem);
52 sa.sa_handler = SIG_IGN;
53 __libc_sigaction(SIGSYNCCALL, &sa, 0);
54 sem_destroy(&barrier_sem);
59 return __syscall_ret(r);
62 void __membarrier_init(void)
64 /* If membarrier is linked, attempt to pre-register to be able to use
65 * the private expedited command before the process becomes multi-
66 * threaded, since registering later has bad, potentially unbounded
67 * latency. This syscall should be essentially free, and it's arguably
68 * a mistake in the API design that registration was even required.
69 * For other commands, registration may impose some cost, so it's left
70 * to the application to do so if desired. Unfortunately this means
71 * library code initialized after the process becomes multi-threaded
72 * cannot use these features without accepting registration latency. */
73 __syscall(SYS_membarrier, MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0);
76 weak_alias(__membarrier, membarrier);