Re: SEGV in x_catch_errors_unwind (x86_64-unknown-linux-gnu)

[Reiner Steib]

On Mon, Feb 13 2006, Richard M. Stallman wrote:

>     > Please describe exactly what actions triggered the bug
>     > and the precise symptoms of the bug:
>
>     `<f1> k [Ctrl <tool-bar> <help>]'  (But it's not reproducible.)

Today I got another crash at the same point (using the same built as
before):

Program received signal SIGSEGV, Segmentation fault.
x_catch_errors_unwind (dummy=9829361)
    at [...]/emacs/src/xterm.c:7530
7530      Display *dpy = x_error_message->dpy;
(gdb) bt full
#0  x_catch_errors_unwind (dummy=9829361)
    at [...]/emacs/src/xterm.c:7530
        dpy = Variable "dpy" is not available.
(gdb) xbacktrace 
"face-attr-match-p"
"face-spec-match-p"
"frame-set-background-mode"
"x-create-frame-with-faces"
"make-frame"
"make-frame-command"
"call-interactively"
(gdb) 

>     Program received signal SIGSEGV, Segmentation fault.
>     [Switching to Thread 182940272320 (LWP 4018)]
>     x_catch_errors_unwind (dummy=9829361)
>       at [...]/emacs/src/xterm.c:7530
>
> The first question is, what was the immediate cause of the crash?
> Could you please see what instruction crashed, and what data it was
> looking at?
>
> Maybe it was examining x_error_message->dpy.
> What is the value of x_error_message?

In both gdb sessions I get:

(gdb) p x_error_message
$1 = (struct x_error_message_stack *) 0x0
(gdb) pr
0
(gdb) p x_error_message->dpy
Cannot access memory at address 0xc8

(If this is not what you asked for, could you please tell me which gdb
command I should use?)

As I didn't have any crash since November [1] and now two crashes at
the same spot with the 2006-02-08 built, I suspect that one of these
changes (from Stefan) might trigger it:

,----
| revision 1.893
| date: 2006-01-23 22:08:13 +0000;  author: monnier;  state: Exp;  lines: +2 -1
| (x_catch_errors_unwind): Yet another int/Lisp_Object mixup.
| ----------------------------
| revision 1.892
| date: 2006-01-23 02:44:02 +0000;  author: monnier;  state: Exp;  lines: +36 
-20
| Avoid allocating Lisp data from code that can be run from a signal handler.
| (x_error_message): New var to replace x_error_message_string.
| (x_error_catcher, x_catch_errors, x_catch_errors_unwind)
| (x_check_errors, x_had_errors_p, x_clear_errors, x_error_handler)
| (syms_of_xterm): Use it instead of x_error_message_string.
`----

Should I build again?  Should I enable additional checks
(ENABLE_CHECKING?)?

Bye, Reiner.

[1] http://thread.gmane.org/gmane.emacs.pretest.bugs/10235
-- 
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      (o o)
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