Re: [PATCH] [gdb/testsuite] Require hw watchpoint in gdb.ada/task_watch.exp

[Tom de Vries <tdevries@suse.de>]

On 11/28/22 17:51, Carl Love wrote:
> Tom:
> 
> On Mon, 2022-11-28 at 12:56 +0100, Tom de Vries wrote:
>> From: Tom de Vries <tdevries@loganberry-1.arch.suse.de>
>>
>> On powerpc64le-linux I run into:
>> ...
>> (gdb) PASS: gdb.ada/task_watch.exp: info tasks before inserting
>> breakpoint
>> watch -location value task 3^M
>> Watchpoint 2: -location value^M
>> (gdb) PASS: gdb.ada/task_watch.exp: watch -location value task 3
>> continue^M
>> Continuing.^M
>> [Thread 0x7ffff7ccf170 (LWP 65550) exited]^M
>> [Thread 0x7ffff7abf170 (LWP 65551) exited]^M
>> FAIL: gdb.ada/task_watch.exp: continue to watchpoint (timeout)
>> ...
>>
>> On x86_64-linux (where the test-case passes), a hardware watchpoint
>> is used:
>> ...
>> (gdb) PASS: gdb.ada/task_watch.exp: info tasks before inserting
>> breakpoint
>> watch -location value task 3^M
>> Hardware watchpoint 2: -location value^M
>> ...
>> and after forcing "set can-use-hw-watchpoints 0" we can
>> intermittently
>> reproduce the same failure.
>>
>> In the gdb documentation related to watchpoints in multi-threaded
>> programs, we
>> read:
>> ...
>> Warning: In multi-threaded programs, software watchpoints have only
>> limited
>> usefulness.  If GDB creates a software watchpoint, it can only watch
>> the value
>> of an expression in a single thread.  If you are confident that the
>> expression
>> can only change due to the current thread’s activity (and if you are
>> also
>> confident that no other thread can become current), then you can use
>> software
>> watchpoints as usual.  However, GDB may not notice when a non-current
>> thread’s
>> activity changes the expression.  (Hardware watchpoints, in contrast,
>> watch an
>> expression in all threads.)
>> ...
>>
>> Since the ada task construct is mapped onto threads, it seems that
>> the
>> same limitation holds for tasks.
>>
>> Fix this by using skip_hw_watchpoint_tests.
>>
>> Tested on powerpc64-linux.
>> ---
>>   gdb/testsuite/gdb.ada/task_watch.exp | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/gdb/testsuite/gdb.ada/task_watch.exp
>> b/gdb/testsuite/gdb.ada/task_watch.exp
>> index b22a6204e90..697074ac164 100644
>> --- a/gdb/testsuite/gdb.ada/task_watch.exp
>> +++ b/gdb/testsuite/gdb.ada/task_watch.exp
>> @@ -19,6 +19,8 @@ load_lib "ada.exp"
>>
>>   if { [skip_ada_tests] } { return -1 }
>>
>> +if { [skip_hw_watchpoint_tests] } { return -1 }
>> +
>>   standard_ada_testfile foo
>>
>>   if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}]
>> != ""} {
> 
> Thanks for looking at the ada test failures.  I have not gotten to
> working on them yet.
> 
> This test passes on Power 10 with/without your patch.
> 
> The test fails on Power 9 since the hw watchpoint support is disabled
> on Power 9 due to an issue.  The patch fixes the test by not running it
> on Power 9.

Thanks Carl, pushed with a tested-by tag.

- Tom