Re: Test 73 Sig_trap fails on arm64 (was Re: [PATCH] perf test: Test 73 Sig_trap fails on s390)

[John Garry]

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@xxxxxxxxxxxxxx/

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 
>
> .