[Bug python/12802] New: Delete breakpoint from Breakpoint.stop

[Bug python/12802] New: Delete breakpoint from Breakpoint.stop

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

           Summary: Delete breakpoint from Breakpoint.stop
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: python
        AssignedTo: unassigned@sourceware.org
        ReportedBy: kevin.pouget@gmail.com


an internal error occurs when you try to `delete' a breakpoint during `stop'
callback:

class MyBP(gdb.Breakpoint):
        def stop(self):
                self.delete()

(gdb) python MyBP(spec="main")
(gdb) run
Starting program: /home/kevin/a.out 
/home/kevin/travail/srcs/git/gdb/gdb/breakpoint.c:4573: internal-error:
bpstat_what: unhandled bptype -1120308712
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

Kevin Pouget <kevin.pouget at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kevin.pouget at gmail dot
                   |                            |com

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[pmuldoon at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

Phil Muldoon <pmuldoon at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pmuldoon at redhat dot com

--- Comment #1 from Phil Muldoon <pmuldoon at redhat dot com> 2011-10-06 14:00:55 UTC ---
I cannot replicate this, can you still replicate it Kevin?

(gdb) file ~/simple
(gdb) python
>class b(gdb.Breakpoint):
>   def stop(self):
>      print "hello"
>      self.delete()
>end
(gdb) py bp = b("main")
Breakpoint 1 at 0x400c48: file simple.c, line 4.
(gdb) r
hello
[Inferior 1 (process 715) exited normally]
(gdb) info breakpoints 
No breakpoints or watchpoints.

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

Kevin Pouget <kevin.pouget at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #2 from Kevin Pouget <kevin.pouget at gmail dot com> 2011-10-06 14:10:47 UTC ---
> I cannot replicate this, can you still replicate it Kevin?

no :)

I double checked, GNU gdb (GDB) Fedora (7.3-43.fc15) does have the bug, so it
was solved by the magic of time! Thanks for looking at it

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[pmuldoon at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

Phil Muldoon <pmuldoon at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |WONTFIX
         AssignedTo|unassigned at sourceware    |pmuldoon at redhat dot com
                   |dot org                     |

--- Comment #3 from Phil Muldoon <pmuldoon at redhat dot com> 2011-10-07 10:17:25 UTC ---
I'm going to change this to wontfix.  Because there may be other stop()
callbacks yet to be processed on that breakpoint, you should not alter or
delete the state of breakpoints.  I've submitted a manual patch to explain what
you can, or cannot do.

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

--- Comment #4 from Kevin Pouget <kevin.pouget at gmail dot com> 2011-10-07 12:14:44 UTC ---
is this a good alternative ?

class MyBP(gdb.Breakpoint):
    def stop(self):
        gdb.post_event(self.delete)


the documentation of gdb.post_event seems not very clear if you don't look at
what is done internally -- I didn't -- but I think it should be safe to do it
this way

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> 2011-10-07 13:23:24 UTC ---
CVSROOT:    /cvs/src
Module name:    src
Changes by:    pmuldoon@sourceware.org    2011-10-07 13:23:19

Modified files:
    gdb/doc        : ChangeLog gdb.texinfo 

Log message:
    2011-10-07  Phil Muldoon  <pmuldoon@redhat.com>

    PR python/12930
    PR python/12802

    * gdb.texinfo (Breakpoints In Python): Clarify behavior in the
    stop method.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/doc/ChangeLog.diff?cvsroot=src&r1=1.1221&r2=1.1222
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/doc/gdb.texinfo.diff?cvsroot=src&r1=1.870&r2=1.871

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[pmuldoon at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

--- Comment #6 from Phil Muldoon <pmuldoon at redhat dot com> 2011-10-07 13:58:42 UTC ---
Yes, I believe so.  But you are still in very dangerous waters.  What happened
if you deleted the breakpoint, but returned "True" from that function.  At the
very least any breakpoint event notification would be broken.  GDB would call
breakpoint stopped observers, but would not have a breakpoint to reference. 
There is nothing to stop you doing it in your scripts, but I would really be
very careful.

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[Bug python/12802] Delete breakpoint from Breakpoint.stop

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12802

Tom Tromey <tromey at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at redhat dot com

--- Comment #7 from Tom Tromey <tromey at redhat dot com> 2011-10-10 19:06:23 UTC ---
(In reply to comment #4)
> is this a good alternative ?
> 
> class MyBP(gdb.Breakpoint):
>     def stop(self):
>         gdb.post_event(self.delete)

I think so.

> the documentation of gdb.post_event seems not very clear if you don't look at
> what is done internally -- I didn't -- but I think it should be safe to do it
> this way

Can you suggest how to fix the docs?

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