[v3,PR,python/18655] Fix deletion of FinishBreakpoints

  Currently, FinishBreakpoints are set at the return address of a frame based on
the `finish' command, and are meant to be temporary breakpoints. However, they
are not being cleaned up after use, as reported in PR python/18655. This was
happening because the disposition of the breakpoint was not being set
correctly.

This commit fixes this issue by correctly setting the disposition in the
post-stop hook of the breakpoint. It also adds a test to ensure this feature
isn't regressed in the future.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18655
---
 gdb/python/py-finishbreakpoint.c              |  2 +-
 .../py-finish-breakpoint-deletion.c           | 31 +++++++++++++
 .../py-finish-breakpoint-deletion.exp         | 43 +++++++++++++++++++
 .../py-finish-breakpoint-deletion.py          | 33 ++++++++++++++
 4 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c
 create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp
 create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py
  

Hi,

On 2022-09-23 16:27, Johnson Sun via Gdb-patches wrote:
> Currently, FinishBreakpoints are set at the return address of a frame based on
> the `finish' command, and are meant to be temporary breakpoints. However, they
> are not being cleaned up after use, as reported in PR python/18655. This was
> happening because the disposition of the breakpoint was not being set
> correctly.
> 
> This commit fixes this issue by correctly setting the disposition in the
> post-stop hook of the breakpoint. It also adds a test to ensure this feature
> isn't regressed in the future.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18655

Whoa, that bug was filed by a younger me, apparently.  Thanks for fixing
it.

Since your patch (the test case) is more than a few obvious lines, I
think that you will need a copyright assignment (unless you have one and
I just don't see it, or your employer has a blanket copyright assignment
and this is done on behalf of your employer).  If you need one, just
follow this form:

  https://git.savannah.gnu.org/cgit/gnulib.git/plain/doc/Copyright/request-assign.future

In the mean time, the patch mostly looks good to me, just some
additional nits.

> ---
>  gdb/python/py-finishbreakpoint.c              |  2 +-
>  .../py-finish-breakpoint-deletion.c           | 31 +++++++++++++
>  .../py-finish-breakpoint-deletion.exp         | 43 +++++++++++++++++++
>  .../py-finish-breakpoint-deletion.py          | 33 ++++++++++++++
>  4 files changed, 108 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c
>  create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp
>  create mode 100644 gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py
> 
> diff --git a/gdb/python/py-finishbreakpoint.c b/gdb/python/py-finishbreakpoint.c
> index c80096f6810..d8b1aff0e2b 100644
> --- a/gdb/python/py-finishbreakpoint.c
> +++ b/gdb/python/py-finishbreakpoint.c
> @@ -145,7 +145,7 @@ bpfinishpy_post_stop_hook (struct gdbpy_breakpoint_object *bp_obj)
>      {
>        /* Can't delete it here, but it will be removed at the next stop.  */
>        disable_breakpoint (bp_obj->bp);
> -      gdb_assert (bp_obj->bp->disposition == disp_del);
> +      bp_obj->bp->disposition = disp_del_at_next_stop;
>      }
>    catch (const gdb_exception &except)
>      {
> diff --git a/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c
> new file mode 100644
> index 00000000000..f09f58861e8
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c
> @@ -0,0 +1,31 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> +   Copyright 2022 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see  <http://www.gnu.org/licenses/>.  */
> +
> +int
> +subroutine (int a)
> +{
> +  return a;
> +}

Not super important, but subroutine could be static.

> +
> +int
> +main ()

main (void)

> +{
> +  int i;
> +  for (i = 0; i < 5; i++)
> +    subroutine (i);
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp
> new file mode 100644
> index 00000000000..25919900a59
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp
> @@ -0,0 +1,43 @@
> +# Copyright (C) 2022 Free Software Foundation, Inc.
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# This file is part of the GDB testsuite.  It checks FinishBreakpoints
> +# are deleted after used.

You can remove the "This file is part of the GDB testsuite" part.  Just
leave:

# Check that FinishBreakpoints are deleted after use.

> +
> +load_lib gdb-python.exp
> +
> +standard_testfile
> +
> +if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
> +    return -1
> +}
> +
> +# Skip all tests if Python scripting is not enabled.
> +if { [skip_python_tests] } { continue }
> +
> +if ![runto_main] then {
> +    return 0
> +}
> +
> +#
> +# Check FinishBreakpoints are deleted after used
> +#

That comment can be removed, it's redundant with what's at the top of
the file.

> +
> +gdb_test "python print (len(gdb.breakpoints()))" "1" "check default BP count"

For consistency, remove the space after "print".

> +gdb_test "source ${srcdir}/${subdir}/${testfile}.py" ".*Python script imported.*" \
> +	 "import python scripts"

Indent that last line with just 4 spaces.

In case somebody uses remote host testing, you should upload the .py
file to the test host first.  See py-unwind.exp for an example.

> +gdb_test "python print (len(gdb.breakpoints()))" "2" "check modified BP count"
> +gdb_test "continue" "Breakpoint.*at.*" "run until FinishBreakpoint stops"
> +gdb_test "python print (len(gdb.breakpoints()))" "2" "check BP count"
> diff --git a/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py
> new file mode 100644
> index 00000000000..f207d0bd2bf
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py
> @@ -0,0 +1,33 @@
> +# Copyright (C) 2022 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# This file is part of the GDB testsuite.  It checks FinishBreakpoints
> +# are deleted after used.

I don't think you need that comment on the .py file: the entry point to
the test is the .exp, this is where the purpose of the test is
documented.

Please format the file using `black`, as described here:

https://sourceware.org/gdb/wiki/Internals%20GDB-Python-Coding-Standards

Simon
  

Hi Simon,

Thanks for reviewing this and filing the bug a few years ago!

I have signed the copyright form and revised the patch.

Will send version 4 shortly.

Cheers,
Johnson