From: "Gerd Möllmann" <gerd.moellmann@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
Subject: Re: gdb doesn't print Lisp backtrace in some circumstances.
Date: Fri, 12 Apr 2024 16:48:24 +0200 [thread overview]
Message-ID: <m2zftyy6vb.fsf@Pro.fritz.box> (raw)
In-Reply-To: <86pluusunr.fsf@gnu.org> (Eli Zaretskii's message of "Fri, 12 Apr 2024 14:11:04 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> 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.
I think it's easier to go through the specbinding stack
(current_thread->m_specdl). For LLDB, I did that in the xbacktrace
function in etc/emacs_lldb.py.
next prev parent reply other threads:[~2024-04-12 14:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-12 10:31 gdb doesn't print Lisp backtrace in some circumstances Alan Mackenzie
2024-04-12 11:11 ` Eli Zaretskii
2024-04-12 11:29 ` Alan Mackenzie
2024-04-12 12:03 ` Eli Zaretskii
2024-04-12 13:18 ` Alan Mackenzie
2024-04-12 13:24 ` Eli Zaretskii
2024-04-13 10:07 ` Alan Mackenzie
2024-04-12 14:48 ` Gerd Möllmann [this message]
2024-04-12 14:56 ` Gerd Möllmann
2024-04-12 15:08 ` Eli Zaretskii
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