Re: [PATCH] perf test: Test 73 Sig_trap fails on s390

[Leo Yan <leo.yan@linaro.org>]

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