Re: [PING^6] [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 12/21/2022 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")
>>>>>