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Re: Help getting backtrace in gdb

From: Noam Postavsky
Subject: Re: Help getting backtrace in gdb
Date: Tue, 27 Jun 2017 17:11:22 -0400

On Mon, Jun 26, 2017 at 2:33 PM, Kaushal Modi <address@hidden> wrote:

> (gdb) break Fsignal
> Breakpoint 3 at 0x605535: file eval.c, line 1508.
> (gdb) r -Q
> Starting program: /home/kmodi/downloads/git/emacs/src/emacs -Q
> (emacs:19646): GLib-GIO-CRITICAL **: g_settings_schema_source_lookup:
> assertion 'source != NULL' failed
> Backtrace:
> [0x0]
> [0x0]
> [0x0]
> During startup program terminated with signal SIGSEGV, Segmentation fault.
> (gdb) bt
> No stack.

It looks like maybe the stack got corrupted so much that gdb can't
find it? (i.e., just bad luck on your part)

> (If interested, this is what causes the crash on emacs -Q:
> http://lists.gnu.org/archive/html/emacs-orgmode/2017-06/msg00508.html )
> The difference in behavior I see is that the breakpoint on Fsignal is not
> working.

I don't think you called Fsignal though? To be clear, the signal
referred to by Fsignal is not related to "signal SIGSEGV", in case
that's what you were thinking.

You can try evaluating (signal 'wrong-number-of-arguments '(x y)) to
see if your Fsignal breakpoint is working.

> I have built emacs from the latest version of master branch with these
> options:
> ./configure options:
>   --with-modules --prefix=/home/kmodi/usr_local/apps/6/emacs/master
> '--program-transform-name=s/^ctags$/ctags_emacs/' 'CPPFLAGS=-fgnu89-inline
> -I/home/kmodi/usr_local/6/include -I/usr/include/freetype2 -I/usr/include'
> 'CFLAGS=-ggdb3 -O0' 'CXXFLAGS=-ggdb3 -O0'
> 'LDFLAGS=-L/home/kmodi/usr_local/6/lib -L/home/kmodi/usr_local/6/lib64
> -ggdb3'

> Has something changed about configure (some new flag that I need to add?) to
> enable debug in gdb?

Nothing should have changed, as far as I know, and those options look
fine (though I wonder what the -fgnu89-inline flag is for).
You can try adding --enable-checking=yes which can help catch errors
earlier (hopefully before your stack gets too corrupted).

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