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Re: uc_sigmask set in a sigaction signal handler not honored




> On Apr  3 14:15, Corinna Vinschen wrote:
> > On Apr  3 11:27, Petr Skočík wrote:
> > > 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:
> >
> > What you're asking for is really complicated.
> >
> > The context given to act is the context at the time the signal function
> > is called.  In Cygwin (lower case w) this is a copy of the context.
> >
> > sigfillset() has not the faintest clue where this context comes from, it
> > just sets the signal mask value without taking any further action.
> >
> > There are no provisions to control if the called function changes the
> > context, other than via setcontext / swapcontext, and I don't see that
> > POSIX requires anything else.  Both functions change the current
> > thread's sigmask according to the value of uc_sigmask.
>
> Or maybe I'm just dumb.  Would it suffice if the thread's signal mask is
> changed to uc_sigmask when the signal function returns?
>
>
> Corinna

Thanks for the feedback.

> Would it suffice if the thread's signal mask is
> changed to uc_sigmask when the signal function returns?

That is the idea. It's what Linux and MacOS do.

Petr Skocik

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