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

  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
  

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")
  

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")
>
  

Ping for: 
<https://sourceware.org/pipermail/gdb-patches/2023-March/198253.html>

Johnson

On 4/10/2023 4:49 AM, JohnsonSun wrote:
> 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")
>>
>
  

> 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 }
This needs to be updated to:

  require allow_python_tests

> +
> +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"

Avoid using hardcoded line numbers.  Either break on a symbol (function)
name, or put a comment in the source code and use gdb_get_line_number.

> 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

I think it would be a bit more straightforward to read if you passed the
arguments to the base class directly:

    def __init__(self):
      super().__init__("i", gdb.BP_WATCHPOINT)
      self.n = 0

I think we can use the super() notation, now that we only support Python
3?

> +
> +    def stop(self):
> +        self.n += 1
> +        print("Watchpoint Hit:", self.n, flush=True)
> +        return False
> +
> +
> +MyBreakpoint("i", gdb.BP_WATCHPOINT)
> +
> +print("Python script imported")

I tried your test with the native-gdbserver and
native-extended-gdbserver boards, and for some reason it doesn't work.
You can try with:

    $ make check TESTS="gdb.python/py-watchpoint.exp" RUNTESTFLAGS="--target_board=native-extended-gdbserver"

In gdb.log:

    ...
    Python script imported
    (gdb) PASS: gdb.python/py-watchpoint.exp: import python scripts
    python print(len(gdb.breakpoints()))
    2
    (gdb) PASS: gdb.python/py-watchpoint.exp: check modified BP count
    gdb_expect_list pattern: /Watchpoint Hit: 1/
    continue
    Continuing.
    Watchpoint Hit: 1
    gdb_expect_list pattern: /Watchpoint Hit: 2/
    FAIL: gdb.python/py-watchpoint.exp: run until program stops (pattern 2) (timeout)

I didn't dig to understand why, but we would need to fix that before
merging.

Simon
  

Hi Simon,

Thanks for reviewing this!  I revised the patch and

will send version 5 shortly.

The new version has been tested on the native-gdbserver and

native-extended-gdbserver boards.

Cheers,
Johnson