bug#16745: Can't send SIGTSTP from Emacs through GDB

bug#16745: Can't send SIGTSTP from Emacs through GDB

[Barry OReilly]

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When running GDB in Emacs and sending SIGTSTP via C-c C-z to another
Emacs ran under GDB, the Emacs under GDB does not appear to receive
the SIGTSTP.

Recipe:

  ./src/emacs -Q
  M-x gdb
  gdb -i=mi src/emacs
  run -Q
  C-c C-z
  [The Emacs under GDB is not stopped.]

However, when I run GDB from the shell rather than from Emacs:

  gdb src/emacs
  run -Q
  C-z
  [The Emacs under GDB stopped.]

I noticed src/.gdbinit has line:

  handle SIGTSTP nopass

So I tried with and without this to no effect.

When I run with these debug statements:

diff --git a/src/process.c b/src/process.c
index 85470b6..176de75 100644
--- a/src/process.c
+++ b/src/process.c
@@ -5753,6 +5753,9 @@ process_send_signal (Lisp_Object process, int signo,
Lisp_Object current_group,
 #else
          sig_char = &t.c_cc[VSUSP];
 #endif
+          { struct timespec debug_ts; char debug_dateStr[20]; {
clock_gettime(CLOCK_REALTIME, &debug_ts); struct tm mytm;
localtime_r(&debug_ts.tv_sec, &mytm); strftime(debug_dateStr, 20,
"%Y-%m-%dT%H:%M:%S", &mytm); }
+               printf( "%s.%09ld|pid:%d|tid:%ld|%s|%d| DEBUG:
sig_char=%02x\n", // TODO: debugging
+                                 debug_dateStr, debug_ts.tv_nsec,
getpid(), pthread_self(), __FILE__, __LINE__, *sig_char ); fflush(stdout); }
          break;
        }

@@ -5901,6 +5904,9 @@ traffic.  */)
 #ifndef SIGTSTP
   error ("No SIGTSTP support");
 #else
+  { struct timespec debug_ts; char debug_dateStr[20]; {
clock_gettime(CLOCK_REALTIME, &debug_ts); struct tm mytm;
localtime_r(&debug_ts.tv_sec, &mytm); strftime(debug_dateStr, 20,
"%Y-%m-%dT%H:%M:%S", &mytm); }
+       printf( "%s.%09ld|pid:%d|tid:%ld|%s|%d| DEBUG: Send SIGTSTP\n", //
TODO: debugging
+                         debug_dateStr, debug_ts.tv_nsec, getpid(),
pthread_self(), __FILE__, __LINE__ ); fflush(stdout); }
   process_send_signal (process, SIGTSTP, current_group, 0);
 #endif
   return process;

The output during the ill recipe is:

2014-02-13T14:11:49.438466000|pid:22430|tid:47532927609088|process.c|5909|
DEBUG: Send SIGTSTP
2014-02-13T14:11:49.438547000|pid:22430|tid:47532927609088|process.c|5758|
DEBUG: sig_char=1a

So the signal is being sent it seems. What might be the obstruction?

I am on RHEL 5, using latest Emacs from trunk and GDB 7.1.

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bug#16745: Can't send SIGTSTP from Emacs through GDB

[Andreas Schwab]

Barry OReilly <gundaetiapo@gmail.com> writes:

> When running GDB in Emacs and sending SIGTSTP via C-c C-z to another
> Emacs ran under GDB, the Emacs under GDB does not appear to receive
> the SIGTSTP.
>
> Recipe:
>
>   ./src/emacs -Q
>   M-x gdb
>   gdb -i=mi src/emacs
>   run -Q
>   C-c C-z
>   [The Emacs under GDB is not stopped.]

Here the signal is sent to terminal process group associated with the
gdb command buffer, which includes the gdb process, but not the inferior
(which runs in its own pty).

> However, when I run GDB from the shell rather than from Emacs:
>
>   gdb src/emacs
>   run -Q
>   C-z
>   [The Emacs under GDB stopped.]

Here the terminal sends the signal to the foreground process group,
which includes the inferior (and not gdb).

This problem does not appear with the traditional gdb interface, since
it closely resembles the shell setup.  I recommend using gud-gdb
instead.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

bug#16745: Can't send SIGTSTP from Emacs through GDB

[Barry OReilly]

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Thanks, just tried gud-gdb and it works well. Actually, the windowing
behavior is saner than when using gdb, so I think I'll prefer gud-gdb.

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bug#16745: Can't send SIGTSTP from Emacs through GDB

[Daimrod]

Barry OReilly <gundaetiapo@gmail.com> writes:
Hi,

> When running GDB in Emacs and sending SIGTSTP via C-c C-z to another
> Emacs ran under GDB, the Emacs under GDB does not appear to receive
> the SIGTSTP.
>
> Recipe:
>
>   ./src/emacs -Q
>   M-x gdb
>   gdb -i=mi src/emacs
>   run -Q
>   C-c C-z
>   [The Emacs under GDB is not stopped.]

I use the following workaround:
1. switch to the buffer *input/output of <program>*
2. C-q C-z RET

-- 
Daimrod/Greg