uc_sigmask set in a sigaction signal handler not honored

[Petr Skočík]

Hi. Correct me if I'm wrong but POSIX appears to define

https://pubs.opengroup.org/onlinepubs/7908799/xsh/ucontext.h.html

as, among other things, containing the field:

sigset_t    uc_sigmask  the set of signals that are blocked when this
                        context is active

and it also specifies that the third argument to a .sa_sigaction
signal handler is a ucontext_t* cast to void*.

So it should follow that doing

void act(int Sig, siginfo_t *Info, void *Uctx)
{
        ucontext_t *uctx = Uctx;
        sigfillset(&uctx->uc_sigmask);
}

from a signal handler should alter the signal mask of the thread the
signal ran on.

This is how Linux and MacOS behave, but not CygWin, as the following
program shows:

#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/time.h>
void prmask(void)
{
        sigset_t mask; pthread_sigmask(SIG_SETMASK,0,&mask);
        for(int i=1; i<=64; i++){ printf("%d", sigismember(&mask,i)); } 
puts("");
}
void act(int Sig, siginfo_t *Info, void *Uctx)
{
        ucontext_t *uctx = Uctx;
        sigfillset(&uctx->uc_sigmask);
}
int main()
{
        struct sigaction sa;
        sa.sa_sigaction = act;
        sa.sa_flags = SA_SIGINFO;
        sigfillset(&sa.sa_mask);

        prmask();
        sigaction(SIGINT,&sa,0);
        sigaction(SIGALRM,&sa,0);
        if(1)
                setitimer(ITIMER_REAL,&(struct 
itimerval){.it_value={.tv_usec=10000}},0);
        pause();
        prmask();
}

I think this is a bug, so I'm reporting it. Do you think it can be fixed
in the near future?

Best regards,
Petr Skocik


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