bug#71744: 29.4; SIGSEGV during completion-at-point in lsp-mode with corfu and cape

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 16 Aug 2024 21:37:29 -0700
> Cc: sigve.indregard@pm.me, 71744@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> 
> > Paul, do you agree that we should simply mark 'c' as volatile, or do you
> > think this needs further investigation on the GCC side (because of the
> > lack of a -Wclobbered warning being issued, or because of the weird
> > code)?
> 
> We definitely should mark 'c' as volatile, or do something equivalent, 
> because the Emacs code violates the C standard.
> 
> Also, if my hypothesis of the mistaken identifier is correct, we should 
> stop ignoring -Wclobbered, and instead pacify GCC without using 
> -Wclobbered. That way, when we screw up in setjmp related code, we'll 
> get *some* warning that *something* is being clobbered, and can investigate.
> 
> To do that, I installed the attached patches into the Emacs master 
> branch. While looking into this I noticed several uses of clobbered 
> variables (i.e., violations of the C standard) and fixed them. Patches 
> 0001-0004 fix these similar bugs elsewhere. Patch 0005 implements your 
> suggestion and should fix Bug#71744. Patch 0006 is a minor performance 
> improvement over Patch 0005.
> 
> Please give these patches a try. Patch 0005 is simple and if it works 
> for the original bug reporter we should be able to close the bug report 
> as fixed.

Thanks, but since the original bug exists on the emacs-30 release
branch and causes crashes, we need to install some part of these
patches on the emacs-30 branch.  Can you please suggest for the
release branch some safe subset of this, which targets the known issue
in read_char?  Is it Patch #5 without removing the -Wclobbered
diagnostic?  Or is it something else?