Re: MPS: a random backtrace while toying with gdb

[Pip Cet <pipcet@protonmail.com>]

On Sunday, June 30th, 2024 at 20:09, Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Sun, 30 Jun 2024 19:25:36 +0000
> 
> > From: Pip Cet pipcet@protonmail.com
> > Cc: Eli Zaretskii eliz@gnu.org, gerd.moellmann@gmail.com, yantar92@posteo.net,
> > emacs-devel@gnu.org
> > 
> > IIUC the consensus is you can set an "int" or "bool" to true, or write to a self-pipe, but that's about as much as you should ever do in a signal handler...
> 
> That's not true, AFAIU: you can safely call any of the dozens of
> functions listed by the signal-safety(7) man page.

I think the implication is reversed there: functions that aren't on that man page definitely aren't safe to call, but that doesn't mean that any old C code modifying complicated structures using only the listed functions is safe, at all.

My point is that complicated C structures, such as the queue Helmut implemented, cannot usually be safely modified from signal handlers unless the non-signal code takes care to block signals while it is modifying the structure.

All that said, it's not like our existing code looks safe, either, so the patch is definitely an improvement!

Pip