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bug#6962: 24.0.90; M-x gdb: hangs when leaving the gdb


From: Steve Revilak
Subject: bug#6962: 24.0.90; M-x gdb: hangs when leaving the gdb
Date: Thu, 6 Oct 2011 20:16:36 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

This bug report will be sent to the Bug-GNU-Emacs mailing list
and the GNU bug tracker at debbugs.gnu.org.  Please check that
the From: line contains a valid email address.  After a delay of up
to one day, you should receive an acknowledgement at that address.

Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':

==================================================================
In the emacs 24.0.90 pretest, I've noticed that gdb-mi hangs when
quitting the debugger.  This seems similar to bug 6962 (opened Sep. 1,
2010), so I'm going file my report under bug 6962.


For illustration, I'll use this C program, in file foo.c

---------------------------------
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char ** argv) {
   if (argc != 2) {
     exit(1);
   }

   return 0;
}
---------------------------------

I'll compile foo.c as follows:

$ make CFLAGS=-g foo
cc -g    foo.c   -o foo


I'll walk through two examples: one that produces a zero exit code,
and one that produces a non-zero exit code.

(1) start emacs as follows:

   emacs -Q foo.c

(2) M-x gdb RET

   Emacs prompts: Run gdb (like this): gdb -i=mi foo
   Type RET to accept the suggested gdb command line

(3) emacs responds with the following:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Current directory is ~/
GNU gdb (GDB) SUSE (7.2-3.3)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-suse-linux".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/srevilak/foo...done.
(gdb) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(4) at the (gdb) prompt, type b main RET
     run RET

(5) gdb stops at the breakpoint in the first line of main.  At the
     (gdb) prompt type

     cont RET

(6) The *gud-foo* buffer outputs

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(gdb) cont
Continuing.
(gdb)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note: gdb does not state the the program has exited, and does not
report the program's exit code.

(7) at the (gdb) prompt, type
   quit RET

At this point, the *gud-foo* buffer hangs, and I have to use C-x k to
kill the buffer.

                                 * * *

That was the non-zero exit case.  Here is the zero exit case

  - M-x gdb RET
  - press RET at the minibuffer's "Run gdb" message
  - type "set args x RET" at the (gdb) prompt
  - type "run RET" at (gdb) prompt
  - *gud-foo* produces the same output as shown in step (6)
  - typing "quit RET" at the (gdb) prompt causes *gud-foo* to hang.


I feel that there are two issues here:

   1. gdb-mi does not state when the debugged program exits.  I believe
      the exit information is very useful to someone debugging a
      program.  For example, I'd like to know that the program exited.

   2. "quit RET" causes gdb-mi to hang.  It would be nice for gdb-mi to
       offer feedback here.  Like "Debugger finished" or some such.


In terms of the expectations behind issues 1. and 2., mine are based
on the behavior of M-x gud-gdb.  For example, gud-gdb offers something
like the following when the debugged program exits:

   Program exited with code 01.

and typing "quit RET" at gud-gdb's (gdb) prompt produces the feedback

   Debugger finished

I think it would be helpful to users if gdb-mi followed these
conventions.


==================================================================

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
     `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/usr/local/emacs-24.0.90.1/share/emacs/24.0.90/etc/DEBUG.


In GNU Emacs 24.0.90.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.22.1)
  of 2011-09-27 on sunny
Windowing system distributor `The X.Org Foundation', version 11.0.10903000
configured using `configure  '--prefix=/usr/local/emacs-24.0.90.1/''

Important settings:
   value of $LC_ALL: nil
   value of $LC_COLLATE: C
   value of $LC_CTYPE: nil
   value of $LC_MESSAGES: nil
   value of $LC_MONETARY: nil
   value of $LC_NUMERIC: nil
   value of $LC_TIME: nil
   value of $LANG: en_US.UTF-8
   value of $XMODIFIERS: @im=local
   locale-coding-system: utf-8-unix
   default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent input:
<down-mouse-1> <mouse-1> M-x r e o <backspace> p o r t - e m a c s - b u <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr message format-spec rfc822 mml easymenu
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mailabbrev mail-utils gmm-utils mailheader
emacsbug time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel
x-win x-dnd tool-bar dnd fontset image fringe lisp-mode register page
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syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
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multi-tty emacs)

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