[PING] [PATCH v4] [PR python/29603] Disable out-of-scope watchpoints

[Johnson Sun <j3.soon777@gmail.com>]

I forgot to add the `[PING]` prefix in the last email. Corrected in this 
email. Thanks.

Johnson

On 4/10/2023 4:47 AM, JohnsonSun wrote:
> Ping for: 
> <https://sourceware.org/pipermail/gdb-patches/2023-March/198253.html>
>
> Johnson
>
> On 3/24/2023 2:31 AM, Johnson Sun wrote:
>> 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
>> ---
>>   gdb/breakpoint.c                           |  1 +
>>   gdb/testsuite/gdb.python/py-watchpoint.c   | 27 +++++++++++
>>   gdb/testsuite/gdb.python/py-watchpoint.exp | 54 ++++++++++++++++++++++
>>   gdb/testsuite/gdb.python/py-watchpoint.py  | 30 ++++++++++++
>>   4 files changed, 112 insertions(+)
>>   create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.c
>>   create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.exp
>>   create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.py
>>
>> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
>> index bff3bac7d1..47dcf1e127 100644
>> --- a/gdb/breakpoint.c
>> +++ b/gdb/breakpoint.c
>> @@ -1832,6 +1832,7 @@ watchpoint_del_at_next_stop (struct watchpoint *w)
>>         w->related_breakpoint = w;
>>       }
>>     w->disposition = disp_del_at_next_stop;
>> +  disable_breakpoint (w);
>>   }
>>     /* Extract a bitfield value from value VAL using the bit 
>> parameters contained in
>> diff --git a/gdb/testsuite/gdb.python/py-watchpoint.c 
>> b/gdb/testsuite/gdb.python/py-watchpoint.c
>> new file mode 100644
>> index 0000000000..0c58b31647
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.python/py-watchpoint.c
>> @@ -0,0 +1,27 @@
>> +/* 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/>.  */
>> +
>> +#include <stdio.h>
>> +
>> +int
>> +main (void)
>> +{
>> +  int i = -1;
>> +  for (i = 0; i < 3; i++)
>> +    printf ("%d", i);
>> +  return 0;
>> +}
>> diff --git a/gdb/testsuite/gdb.python/py-watchpoint.exp 
>> b/gdb/testsuite/gdb.python/py-watchpoint.exp
>> new file mode 100644
>> index 0000000000..5504736629
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.python/py-watchpoint.exp
>> @@ -0,0 +1,54 @@
>> +# 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/>.
>> +
>> +# Check that Watchpoints 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
>> +}
>> +
>> +# For remote host testing
>> +set pyfile [gdb_remote_download host 
>> ${srcdir}/${subdir}/${testfile}.py]
>> +
>> +gdb_test_no_output "set can-use-hw-watchpoints 0" "don't use 
>> hardware watchpoints"
>> +gdb_test "break 24" ".*" "set breakpoint before loop"
>> +gdb_test "continue" ".*" "run until reaching loop"
>> +gdb_test "clear" ".*" "delete the breakpoint before loop"
>> +gdb_test "python print(len(gdb.breakpoints()))" "1" "check default 
>> BP count"
>> +gdb_test "source $pyfile" ".*Python script imported.*" \
>> +    "import python scripts"
>> +gdb_test "python print(len(gdb.breakpoints()))" "2" "check modified 
>> BP count"
>> +gdb_test_sequence "continue" "run until program stops" {
>> +    "Watchpoint Hit: 1"
>> +    "Watchpoint Hit: 2"
>> +    "Watchpoint Hit: 3"
>> +    "Watchpoint Hit: 4"
>> +    "Watchpoint 3 deleted because the program has left the block in"
>> +    "which its expression is valid\."
>> +    "Watchpoint Hit: 5"
>> +    "012\\[Inferior 1 \\(process .*\\) exited normally\\]"
>> +}
>> +gdb_test "python print(len(gdb.breakpoints()))" "1" "check BP count"
>> diff --git a/gdb/testsuite/gdb.python/py-watchpoint.py 
>> b/gdb/testsuite/gdb.python/py-watchpoint.py
>> new file mode 100644
>> index 0000000000..c5fae00e93
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.python/py-watchpoint.py
>> @@ -0,0 +1,30 @@
>> +# 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/>.
>> +
>> +
>> +class MyBreakpoint(gdb.Breakpoint):
>> +    def __init__(self, *args, **kwargs):
>> +        gdb.Breakpoint.__init__(self, *args, **kwargs)
>> +        self.n = 0
>> +
>> +    def stop(self):
>> +        self.n += 1
>> +        print("Watchpoint Hit:", self.n, flush=True)
>> +        return False
>> +
>> +
>> +MyBreakpoint("i", gdb.BP_WATCHPOINT)
>> +
>> +print("Python script imported")
>