Re: gdb doesn't print Lisp backtrace in some circumstances.

[Eli Zaretskii]

> Date: Fri, 12 Apr 2024 10:31:53 +0000
> From: Alan Mackenzie <acm@muc.de>
> 
> Yesterday I got a core dump from a segmentation fault in Emacs (my
> development version, not master).  I loaded this into gdb inside Emacs
> to have a look at it.
> 
> The backtrace command output the C data as it should, but on coming to
> the Lisp backtrace gave an error message about there needing to be a
> process running to "do this".  (I don't have the exact message any
> more.)  It would seem these fancy Lisp facilities only work when the
> process that produced them is still running.

Yes, because they call functions inside Emacs to format Lisp objects.

> All the information required to produce this Lisp backtrace is present
> in the core dump.  Would it be possible, perhaps, to modify our .gdbinit
> to use the running Emacs to process the core dump, or something like
> that?

I don't think so, no.  But you can reproduce the Lisp backtrace
manually (albeit tediously, by going over all the calls to Ffuncall,
eval_sub and suchlikes, and displaying their arg[0].  If it's a
symbol, typing xsymbol should show you the Lisp function being called.
If it is not a symbol, you could use xcar/xcdr etc., but that is much
more tedious, and I usually give up on those frames in the stack.