bug#74831: 31.0.50; scratch/igc: segfaults on startup when called under gdb

[Eli Zaretskii]

> Date: Thu, 12 Dec 2024 15:26:32 +0100
> From:  Gregor Zattler via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x0000555555779816 in XSETCDR (c=..., n=n@entry=...) at ./src/lisp.h:1605
> 1605    *xcdr_addr (c) = n;

So what is the value of xcdr_addr(s) here?  It looks like
dereferencing it causes the segfault, so its value might give us some
hints.

Also, where did you start GDB?  It looks like you started it not from
the Emacs' src/ directory, in which case please say

  (gdb) source /path/to/emacs/src/.gdbinit

before running Emacs.  That's because the MPS library uses SIGSEGV for
its memory barriers, and .gdbinit there makes sure such SIGSEGVs don't
stop Emacs.  IOW, this could be a false positive, not a real segfault.