bug#53136: 28.0.90; segfault in lock_file

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: 53136@debbugs.gnu.org
> Date: Sun, 09 Jan 2022 16:10:42 +0800
> 
> >>       memcpy (dot, replacement, replacementlen);
> >> 
> >> Ends up writing one byte outside dot.
> >> 
> >> I could not find the problem, but someone else may want to take a look.
> 
> > Details, please: the values of all the relevant variables at that
> > point, including the contents of all the string variables.
> 
> gdb says dot is "optimized out" (but valgrind, which I happened to be
> running that Emacs under in an attempt to catch the GC bug I reported a
> month ago, disagrees).  pidlen is 6.
> 
> I will try to get more information from the valgrind core file.

Thanks.

> > And what is your value of MAX_LFINFO?
> 
> MAX_LFINFO is 8192.

So we somehow wrote more than 8192 bytes by that memcpy line?  I find
this hard to believe.

What exactly did valgrind say?