Re: [PING^4] [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 12/5/2022 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")
>>>