Re: [RFC/PATCH] Add new internal variable $_signo

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Sergio Durigan Junior <sergiodj@redhat.com>
> Date: Thu, 13 Jun 2013 21:37:59 -0300
> 
> Hi,
> 
> This patch comes from a request at:
> 
> <https://bugzilla.redhat.com/show_bug.cgi?id=971849>
> 
> Basically, the ABRT project (<https://fedorahosted.org/abrt/wiki>) wants
> to be able to perform some analysis on corefiles (to be implemented as a
> Python GDB module) and for that it needs to be able to inspect the
> signal which killed the program being investigated.
> 
> This can be done with recent Linux kernels by inspecting the $_siginfo
> convenience variable (on corefiles, it works by parsing the contents of
> the NT_SIGINFO section, whose support was added by Tom on
> 1b05b77b857f26c59ad5dc6443fc8baa21696440).  The NT_SIGINFO section was
> added on the kernel by:
> 
>   author   Denys Vlasenko <vda.linux@googlemail.com>      2012-10-05 00:15:35 (GMT)
>   commit         49ae4d4b113be03dc4a2ec5f2a1f573ff0fcddb3 (patch)
> 
> (This is Linux 3.7-rc1).
> 
> Well, the problem is that for older kernels (or not so old, as can be
> noted by the date), when one tries to access $_siginfo.si_signo from a
> corefile he/she gets:
> 
>   (gdb) core ./coredump
>   [New LWP 2703]
>   Core was generated by `/usr/bin/gnote <<skip>>'.
>   Program terminated with signal 11, Segmentation fault.
>   #0  0x09fa5348 in ?? ()
>   (gdb) print $_siginfo.si_signo
>   Unable to read siginfo
> 
> The signal can obviously be recovered because GDB itself mentioned it
> when saying that it was "signal 11, Segmentation fault", and this is why
> this patch came to life.  It basically sets/creates a new internal
> variable called "$_signo" to be used as an alternative to
> $_siginfo.si_signo when this one is unavailable.  It's not a complex
> patch per se, but I would certainly like some review because there may
> be other places where we should set the variable as well.
> 
> The patch also contains a testcase and an update to the documentation in
> order to mention the new convenience variable.
> 
> Comments?  OK to apply?

Sounds reasonable to me.  Implementation seems sound.

> gdb/ChangeLog:
> 2013-06-13  Denys Vlasenko  <dvlasenk@redhat.com>
> 
> 	* corelow.c (core_open): Set internal variable "$_signo".
> 	* infrun.c (handle_inferior_event): Likewise, for
> 	TARGET_WAITKIND_SIGNALLED and TARGET_WAITKIND_STOPPED.
> 
> gdb/testsuite/ChangeLog:
> 2013-06-13  Sergio Durigan Junior  <sergiodj@redhat.com>
> 
> 	* gdb.base/signo.c: New file.
> 	* gdb.base/signo.exp: Likewise.
> 
> gdb/doc/ChangeLog:
> 2013-06-13  Sergio Durigan Junior  <sergiodj@redhat.com>
> 
> 	* gdb.texinfo (Convenience Variables): Document "$_signo".