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Date:   Tue, 15 Feb 2022 11:16:16 +0000
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Subject: Re: Test 73 Sig_trap fails on arm64 (was Re: [PATCH] perf test: Test
 73 Sig_trap fails on s390)
From:   John Garry <john.garry@huawei.com>
To:     Leo Yan <leo.yan@linaro.org>, Marco Elver <elver@google.com>,
        Will Deacon <will@kernel.org>
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On 24/01/2022 09:19, John Garry wrote:

Hi Will,

Have you had a chance to check this or the mail from Dmitry?

https://lore.kernel.org/linux-perf-users/CACT4Y+YVyJcqbR5j2fsSQ+C5hy78X+aobrUHaZKghFf0_NMv=A@mail.gmail.com/

If we can't make progress then we just need to skip the test on arm64 
for now.

Thanks,
John

> 
>> On Tue, Jan 18, 2022 at 12:40:04PM +0100, Marco Elver wrote:
>>
>> [...]
>>
>>>> Both Arm and Arm64 platforms cannot support signal handler with
>>>> breakpoint, please see the details in [1].  So I think we need
>>>> something like below:
>>>>
>>>> static int test__sigtrap(struct test_suite *test __maybe_unused, int 
>>>> subtest __maybe_unused)
>>>> {
>>>>          ...
>>>>
>>>>          if (!BP_SIGNAL_IS_SUPPORTED) {
>>>>                  pr_debug("Test not supported on this architecture");
>>>>                  return TEST_SKIP;
>>>>          }
>>>>
>>>>          ...
>>>> }
>>>>
>>>> Since we have defined BP_SIGNAL_IS_SUPPORTED, I think we can reuse 
>>>> it at
>>>> here.
>>>>
>>>> [1]https://lore.kernel.org/lkml/157169993406.29376.12473771029179755767.tip-bot2@tip-bot2/ 
>>>>
>>> Does this limitation also exist for address watchpoints? The sigtrap
>>> test does not make use of instruction breakpoints, but instead just
>>> sets up a watchpoint on access to a data address.
>> Yes, after reading the code, the flow for either instrution breakpoint
>> or watchpoint both use the single step [1], thus the signal handler will
>> take the single step execution and lead to the infinite loop.
>>
>> I am not the best person to answer this question; @Will, could you
>> confirm for this?  Thanks!
>>
>> Leo
>>
>> [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kernel/hw_breakpoint.c 
>>
> 
> .