bug#47067: 28.0.50; [feature/native-comp] Crash while scrolling through dispnew.c

[Andrea Corallo]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Andrea Corallo <akrl@sdf.org>
>> Cc: 47067@debbugs.gnu.org
>> Date: Fri, 12 Mar 2021 15:27:30 +0000
>> 
>> Generally speaking the first step is to identify the function that is
>> responsible for the bug, this is often on the top of the back-trace but
>> not necessarily.  In the unfortunate case I typically proceed by
>> bisection.
>
> In my case the top of the stack looks like this:
>
>   #0  0x01236788 in arithcompare_driver (nargs=2, args=0x28,
>       comparison=ARITH_LESS) at data.c:2673
>   #1  0x01236860 in Flss (nargs=2, args=0x28) at data.c:2691
>   #2  0x0a872285 in ?? ()
>   #3  0x01261898 in funcall_lambda (fun=XIL(0xa00000000a0bf230), nargs=5,
>       arg_vector=0x826a08) at eval.c:3292
>   #4  0x012601ed in Ffuncall (nargs=6, args=0x826a00) at eval.c:3013
>   #5  0x0a8e0dbf in ?? ()
>   #6  0x012601ed in Ffuncall (nargs=1, args=0x826bd8) at eval.c:3013
>   #7  0x0a8ce041 in ?? ()
>   #8  0x01261898 in funcall_lambda (fun=XIL(0xa0000000069f2a50), nargs=1,
>       arg_vector=0x826db8) at eval.c:3292
>   #9  0x012601ed in Ffuncall (nargs=2, args=0x826db0) at eval.c:3013
>   #10 0x70895b36 in 
> F632d666f6e742d6c6f636b2d6375742d6f66662d6465636c617261746f7273_c_font_lock_cut_off_declarators_0
>  ()
>      from 
> d:\usr\eli\.emacs.d\eln-cache\28.0.50-7d88f6c1\cc-fonts-d7d8a7f5-b7c359cd.eln
>   #11 0x01261898 in funcall_lambda (fun=XIL(0xa0000000079249a0), nargs=1,
>       arg_vector=0x827050) at eval.c:3292
>   #12 0x012601ed in Ffuncall (nargs=2, args=0x827048) at eval.c:3013
>
> And the corresponding Lisp backtrace:
>
>   "c-beginning-of-statement-1" (0x826a08)
>   "c-just-after-func-arglist-p" (0x826be0)
>   "c-back-over-member-initializers" (0x826db8)
>   "c-font-lock-cut-off-declarators" (0x827050)
>   "font-lock-fontify-keywords-region" (0x8273a8)
>   "font-lock-default-fontify-region" (0x8276b8)
>
> (Don't ask me why "<", i.e. Flss, doesn't appear in the Lisp
> backtrace: something strange happens with backtraces here, as I will
> describe in another message.  I think the "??" things in the backtrace
> are related.)
>
> How do I go about finding the function that's responsible for the
> problem given the above?  The problem is 100% reproducible for me.

One easy option is to evaluate say `c-beginning-of-statement-1' (as
first defendant) and see if afterwards it still crashes.  Same one can
load entire files to exclude entirely their content from the equation.

>> Here the problem is that being not reproducible we are stuck in the
>> first steps, reproducibility is tipically a pre for this kind of
>> analysis.  But again if it's a miscompilation it *must* be reproducible
>> because code is not morphing so probably we are not reproducing it
>> precisely?
>
> Here's another reproducer:
>
>   emacs -Q
>   C-x C-f src/dispnew.c
>   C-s sleep-for
>
> I usually get a SIGSEGV before I even type the whole of "sleep-for".

Can't reproduce this either :(  That's odd.

> Do you have all of the cc-*.el files natively-compiled?  I do.

Looks so.

Thanks

  Andrea