[Bug python/29603] New: Python Watchpoints are not deleted

[Bug python/29603] New: Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

            Bug ID: 29603
           Summary: Python Watchpoints are not deleted
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: python
          Assignee: unassigned at sourceware dot org
          Reporter: j3.soon777 at gmail dot com
  Target Milestone: ---

In Python, if we register a local software watchpoint and set the
`Breakpoint.stop' function to always return `False', the watchpoint will not be
deleted when going out of scope.

This cause gdb to incorrectly trigger the `Breakpoint.stop' function many more
times than it should.

This issue is reproduced in:
- GCC 7.5.0 & GDB 10.2 on Ubuntu 18.04,
- GCC 9.3.0 & GDB 9.2 on Ubuntu 20.04 (WSL on Windows),
- GCC 11.2.0 & GDB 12.0.90 on Ubuntu 22.04,
- and on current GDB HEAD (commit 8e037eae6823caf5b9cb5b4feb3de838abb25956).

Please see the attachment for the testing files.

Commands to reproduce:

        gcc -g test.c
        gdb a.out
        (gdb) set can-use-hw-watchpoints 0
        (gdb) b main
        (gdb) r
        (gdb) source test.py
        (gdb) c
        Continuing.
        Watchpoint Hit: 1
        Watchpoint Hit: 2
        Watchpoint Hit: 3

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 4

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 5

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 6

        ...

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 1201

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 1202

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        Watchpoint Hit: 1203
        [Inferior 1 (process 17119) exited normally]

Please note that the Watchpoint in the test file should only be hit 4 times.

I'm currently working on a patch to fix this bug.

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[Bug python/29603] Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

Johnson Sun <j3.soon777 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |j3.soon777 at gmail dot com

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[Bug python/29603] Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

--- Comment #1 from Johnson Sun <j3.soon777 at gmail dot com> ---
Created attachment 14352
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14352&action=edit
Test C code

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[Bug python/29603] Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

--- Comment #2 from Johnson Sun <j3.soon777 at gmail dot com> ---
Created attachment 14353
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14353&action=edit
Test Python code

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[Bug python/29603] Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

--- Comment #3 from Johnson Sun <j3.soon777 at gmail dot com> ---
Just send a patch to fix this issue. Please refer to:
https://sourceware.org/pipermail/gdb-patches/2022-September/192098.html

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[Bug python/29603] Python Watchpoints are not deleted

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Simon Marchi <simark@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb

commit 6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb
Author: Johnson Sun <j3.soon777@gmail.com>
Date:   Thu May 11 23:46:20 2023 +0800

    Disable out-of-scope watchpoints

    Currently, when a local software watchpoint goes out of scope, GDB sets
    the watchpoint's disposition to `delete at next stop' and then normal
    stops (i.e., stop and wait for the next GDB command). When GDB normal
    stops, it automatically deletes the breakpoints with their disposition
    set to `delete at next stop'.

    Suppose a Python script decides not to normal stop when a local
    software watchpoint goes out of scope, the watchpoint will not be
    automatically deleted even when its disposition is set to
    `delete at next stop'.

    Since GDB single-steps the program and tests the watched expression
    after each instruction, not deleting the watchpoint causes the
    watchpoint to be hit many more times than it should, as reported in
    PR python/29603.

    This was happening because the watchpoint is not deleted or disabled
    when going out of scope.

    This commit fixes this issue by disabling the watchpoint when going out
    of scope. It also adds a test to ensure this feature isn't regressed in
    the future.

    Calling `breakpoint_auto_delete' on all kinds of stops (in
    `fetch_inferior_event') seem to solve this issue, but is in fact
    inappropriate, since `breakpoint_auto_delete' goes over all breakpoints
    instead of just going through the bpstat chain (which only contains the
    breakpoints that were hit right now).

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603
    Change-Id: Ia85e670b2bcba2799219abe4b6be3b582387e383

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[Bug python/29603] Python Watchpoints are not deleted

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org

--- Comment #5 from Hannes Domani <ssbssa at sourceware dot org> ---
(In reply to Sourceware Commits from comment #4)
> The master branch has been updated by Simon Marchi <simark@sourceware.org>:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;
> h=6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb
> 
> commit 6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb
> Author: Johnson Sun <j3.soon777@gmail.com>
> Date:   Thu May 11 23:46:20 2023 +0800
> 
>     Disable out-of-scope watchpoints
>     
>     Currently, when a local software watchpoint goes out of scope, GDB sets
>     the watchpoint's disposition to `delete at next stop' and then normal
>     stops (i.e., stop and wait for the next GDB command). When GDB normal
>     stops, it automatically deletes the breakpoints with their disposition
>     set to `delete at next stop'.
>     
>     Suppose a Python script decides not to normal stop when a local
>     software watchpoint goes out of scope, the watchpoint will not be
>     automatically deleted even when its disposition is set to
>     `delete at next stop'.
>     
>     Since GDB single-steps the program and tests the watched expression
>     after each instruction, not deleting the watchpoint causes the
>     watchpoint to be hit many more times than it should, as reported in
>     PR python/29603.
>     
>     This was happening because the watchpoint is not deleted or disabled
>     when going out of scope.
>     
>     This commit fixes this issue by disabling the watchpoint when going out
>     of scope. It also adds a test to ensure this feature isn't regressed in
>     the future.
>     
>     Calling `breakpoint_auto_delete' on all kinds of stops (in
>     `fetch_inferior_event') seem to solve this issue, but is in fact
>     inappropriate, since `breakpoint_auto_delete' goes over all breakpoints
>     instead of just going through the bpstat chain (which only contains the
>     breakpoints that were hit right now).
>     
>     Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603
>     Change-Id: Ia85e670b2bcba2799219abe4b6be3b582387e383

Can this be closed?

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[Bug python/29603] Python Watchpoints are not deleted

[j3.soon777 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29603

Johnson Sun <j3.soon777 at gmail dot com> changed:

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

--- Comment #6 from Johnson Sun <j3.soon777 at gmail dot com> ---
(In reply to Hannes Domani from comment #5)
> (In reply to Sourceware Commits from comment #4)
> > The master branch has been updated by Simon Marchi <simark@sourceware.org>:
> > 
> > https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;
> > h=6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb
> > 
> > commit 6e96d8a9702d1fef3eb6de47bb84bdea578eb1bb
> > Author: Johnson Sun <j3.soon777@gmail.com>
> > Date:   Thu May 11 23:46:20 2023 +0800
> > 
> >     Disable out-of-scope watchpoints
> >     
> >     Currently, when a local software watchpoint goes out of scope, GDB sets
> >     the watchpoint's disposition to `delete at next stop' and then normal
> >     stops (i.e., stop and wait for the next GDB command). When GDB normal
> >     stops, it automatically deletes the breakpoints with their disposition
> >     set to `delete at next stop'.
> >     
> >     Suppose a Python script decides not to normal stop when a local
> >     software watchpoint goes out of scope, the watchpoint will not be
> >     automatically deleted even when its disposition is set to
> >     `delete at next stop'.
> >     
> >     Since GDB single-steps the program and tests the watched expression
> >     after each instruction, not deleting the watchpoint causes the
> >     watchpoint to be hit many more times than it should, as reported in
> >     PR python/29603.
> >     
> >     This was happening because the watchpoint is not deleted or disabled
> >     when going out of scope.
> >     
> >     This commit fixes this issue by disabling the watchpoint when going out
> >     of scope. It also adds a test to ensure this feature isn't regressed in
> >     the future.
> >     
> >     Calling `breakpoint_auto_delete' on all kinds of stops (in
> >     `fetch_inferior_event') seem to solve this issue, but is in fact
> >     inappropriate, since `breakpoint_auto_delete' goes over all breakpoints
> >     instead of just going through the bpstat chain (which only contains the
> >     breakpoints that were hit right now).
> >     
> >     Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603
> >     Change-Id: Ia85e670b2bcba2799219abe4b6be3b582387e383
> 
> Can this be closed?

Yes, this can be closed. Thank you for the reminder.

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