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Re: [bug-mes] mes lib: signal() function; sigaction() function

From: Jan Nieuwenhuizen
Subject: Re: [bug-mes] mes lib: signal() function; sigaction() function
Date: Thu, 14 Mar 2019 07:41:28 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Danny Milosavljevic writes:

Hi Danny,

> I've fixed signal handling in mes on ARM mostly (it still crashes AFTER the
> signal handler has been called--but at least it calls it now for the first
> time).

Ah, that's progress.

> I'm pretty sure that sa_mask (and sigset_t itself) has to be large enough
> for 64 bits, also on i386 and on x86-64.
> There are three possible syscalls in Linux in order to set up signal handlers,
> * SYS_signal
> * SYS_sigaction
> * SYS_rt_sigaction
> The first and oldest one is a remnant of a time long past where the MIT
> school of design used non-restartable handlers because they were easier
> to implement--and I suggest that we do not support it.
> glibc doesn't support it either.  It always registers restartable handlers
> on signal().
> The second one is better and has BSD signal semantics (which are non-insane).
> The third one is almost entirely like the second one but they found out that
> they need more than 32 signals and thus extended sigset_t.

I didn't take the time to look into this, so your summary really helps,

> So I suggest that you remove all mention of SYS_signal and SIG_sigaction.

Yes, I agree.

> We already implement signal() in terms of SYS_rt_sigaction, but there's a
> strange fallback to SYS_signal which only serves to hide problems in the
> former.  I suggest you remove the fallback.
> Also, there's an empty stub for sigaction() which we can just implement
> in its entirety, copying pretty much the body of signal() from
> lib/linux/signal.c .
> (The only difference between sigaction() and SYS_rt_sigaction() is that the
> latter has an extra argument "sizeof(sigset_t)" at the end but the former
> doesn't)
> What do you think?

I chose to implement that which looked simplest, and oldest and until
now it worked :-)  Time to clean such things up.


Jan Nieuwenhuizen <address@hidden> | GNU LilyPond http://lilypond.org
Freelance IT http://JoyofSource.com | AvatarĀ® http://AvatarAcademy.com

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