source: azure_iot_hub/trunk/musl-1.1.18/src/signal/sigaction.c@ 389

#include <signal.h>
#include <errno.h>
#include <string.h>
#include "syscall.h"
#include "pthread_impl.h"
#include "libc.h"
#include "ksigaction.h"

static int unmask_done;
static unsigned long handler_set[_NSIG/(8*sizeof(long))];

void __get_handler_set(sigset_t *set)
{
        memcpy(set, handler_set, sizeof handler_set);
}

int __libc_sigaction(int sig, const struct sigaction *restrict sa, struct sigaction *restrict old)
{
        struct k_sigaction ksa, ksa_old;
        if (sa) {
                if ((uintptr_t)sa->sa_handler > 1UL) {
                        a_or_l(handler_set+(sig-1)/(8*sizeof(long)),
                                1UL<<(sig-1)%(8*sizeof(long)));

                        /* If pthread_create has not yet been called,
                         * implementation-internal signals might not
                         * yet have been unblocked. They must be
                         * unblocked before any signal handler is
                         * installed, so that an application cannot
                         * receive an illegal sigset_t (with them
                         * blocked) as part of the ucontext_t passed
                         * to the signal handler. */
                        if (!libc.threaded && !unmask_done) {
                                __syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
                                        SIGPT_SET, 0, _NSIG/8);
                                unmask_done = 1;
                        }
                }
                ksa.handler = sa->sa_handler;
                ksa.flags = sa->sa_flags | SA_RESTORER;
                ksa.restorer = (sa->sa_flags & SA_SIGINFO) ? __restore_rt : __restore;
                memcpy(&ksa.mask, &sa->sa_mask, sizeof ksa.mask);
        }
        if (syscall(SYS_rt_sigaction, sig, sa?&ksa:0, old?&ksa_old:0, sizeof ksa.mask))
                return -1;
        if (old) {
                old->sa_handler = ksa_old.handler;
                old->sa_flags = ksa_old.flags;
                memcpy(&old->sa_mask, &ksa_old.mask, sizeof ksa_old.mask);
        }
        return 0;
}

int __sigaction(int sig, const struct sigaction *restrict sa, struct sigaction *restrict old)
{
        if (sig-32U < 3 || sig-1U >= _NSIG-1) {
                errno = EINVAL;
                return -1;
        }
        return __libc_sigaction(sig, sa, old);
}

weak_alias(__sigaction, sigaction);