Re: [PING^5] [PATCH v3] [PR python/29603] Disable out-of-scope watchpoints

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

Ping for: 
<https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.

Johnson

On 12/13/2022 5:44 AM, Johnson Sun wrote:
> Ping for: 
> <https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.
>
> Johnson
>
> On 12/5/2022 12:45 AM, Johnson Sun wrote:
>> Ping for: 
>> <https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.
>>
>> Johnson
>>
>> On 11/25/2022 11:11 PM, Johnson Sun wrote:
>>> Ping for: 
>>> <https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.
>>>
>>> Johnson
>>>
>>> On 11/18/2022 8:17 PM, JohnsonSun wrote:
>>>> Ping for: 
>>>> <https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.
>>>>
>>>> Johnson
>>>>
>>>> On 10/21/2022 2:11 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.
>>>>>
>>>>> Two other solutions seem to solve this issue, but are in fact 
>>>>> inappropriate:
>>>>> 1. Automatically delete breakpoints on all kinds of stops
>>>>>     (in `fetch_inferior_event'). This solution is very slow since 
>>>>> the deletion
>>>>>     requires O(N) time for N breakpoints.
>>>>> 2. Disable the watchpoint after the watchpoint's disposition is 
>>>>> set to
>>>>>     `delete at next stop' (in `watchpoint_del_at_next_stop'). This 
>>>>> solution
>>>>>     modifies a non-extension-related code path, and isn't 
>>>>> preferred since this
>>>>>     issue cannot occur without extension languages. (gdb scripts 
>>>>> always normal
>>>>>     stop before continuing execution)
>>>>>
>>>>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603
>>>>> ---
>>>>>   gdb/breakpoint.c                           |  2 +
>>>>>   gdb/testsuite/gdb.python/py-watchpoint.c   | 27 ++++++++++++
>>>>>   gdb/testsuite/gdb.python/py-watchpoint.exp | 48 
>>>>> ++++++++++++++++++++++
>>>>>   gdb/testsuite/gdb.python/py-watchpoint.py  | 30 ++++++++++++++
>>>>>   4 files changed, 107 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 bff3bac7d1a..15f4ae2131c 100644
>>>>> --- a/gdb/breakpoint.c
>>>>> +++ b/gdb/breakpoint.c
>>>>> @@ -5340,6 +5340,8 @@ bpstat_check_breakpoint_conditions (bpstat 
>>>>> *bs, thread_info *thread)
>>>>>     /* Evaluate extension language breakpoints that have a "stop" 
>>>>> method
>>>>>        implemented.  */
>>>>>     bs->stop = breakpoint_ext_lang_cond_says_stop (b);
>>>>> +  if (b->disposition == disp_del_at_next_stop)
>>>>> +    disable_breakpoint(b);
>>>>>       if (is_watchpoint (b))
>>>>>       {
>>>>> diff --git a/gdb/testsuite/gdb.python/py-watchpoint.c 
>>>>> b/gdb/testsuite/gdb.python/py-watchpoint.c
>>>>> new file mode 100644
>>>>> index 00000000000..4e1760bb05b
>>>>> --- /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;
>>>>> +  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 00000000000..ac58d75c523
>>>>> --- /dev/null
>>>>> +++ b/gdb/testsuite/gdb.python/py-watchpoint.exp
>>>>> @@ -0,0 +1,48 @@
>>>>> +# 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 "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: ."
>>>>> +    "\[\r\n\]+Watchpoint . deleted because the program has left 
>>>>> the block in"
>>>>> +    "\[\r\n\]+which its expression is valid\."
>>>>> +    "Watchpoint Hit: ."
>>>>> +    "\[\r\n\]+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 00000000000..ce5dee118ad
>>>>> --- /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.i = 0
>>>>> +
>>>>> +    def stop(self):
>>>>> +        self.i += 1
>>>>> +        print("Watchpoint Hit:", self.i)
>>>>> +        return False
>>>>> +
>>>>> +
>>>>> +MyBreakpoint("i", gdb.BP_WATCHPOINT)
>>>>> +
>>>>> +print("Python script imported")
>>>>