Re: [PING^7] [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 12/28/2022 12:40 AM, JohnsonSun wrote:
> Ping for: 
> <https://sourceware.org/pipermail/gdb-patches/2022-October/192909.html>.
>
> Johnson
>
> On 12/21/2022 6:08 AM, Johnson Sun wrote:
>> 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")
>>>>>>
>