linux-kernel - Re: [PATCH v2] perf: tests: Disable breakpoint tests on ARM (32-bit)

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Date:   Tue, 27 Nov 2018 19:30:28 +0000
From:   Will Deacon <will.deacon@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Richter <tmricht@...ux.vnet.ibm.com>,
        Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] perf: tests: Disable breakpoint tests on ARM (32-bit)

On Mon, Nov 26, 2018 at 04:31:23PM -0800, Florian Fainelli wrote:
> breakpoint tests on the ARM 32-bit kernel are broken in several ways.
> 
> The breakpoint length requested does not necessarily match whether the
> function address has the Thumb bit (bit 0) set or not, and this does
> matter to the ARM kernel hw_breakpoint infrastructure. See [1] for
> background.
> 
> [1]: https://lkml.org/lkml/2018/11/15/205
> 
> As Will indicated, the overflow handling would require single-stepping
> which is not supported at the moment. Just disable those tests for the
> ARM 32-bit platforms.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
> Changes in v2:
> 
> - Fix comment above test per Will's feedback
> 
>  tools/perf/tests/bp_signal.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/tests/bp_signal.c b/tools/perf/tests/bp_signal.c
> index a467615c5a0e..05bf06f84a3b 100644
> --- a/tools/perf/tests/bp_signal.c
> +++ b/tools/perf/tests/bp_signal.c
> @@ -292,11 +292,11 @@ int test__bp_signal(struct test *test __maybe_unused, int subtest __maybe_unused
>  bool test__bp_signal_is_supported(void)
>  {
>  /*
> - * The powerpc so far does not have support to even create
> + * powerpc, s390 and arm so far does not have support to even create
>   * instruction breakpoint using the perf event interface.
>   * Once it's there we can release this.

Sorry, Florian, but I still think this comment is bogus since you can
create instruction breakpoints via perf on arm. I think you need
something like:

	/*
	 * PowerPC and S390 do not support creation of instruction
	 * breakpoints using the perf_event interface.
	 *
	 * ARM requires explicit rounding down of the instruction
	 * pointer in Thumb mode, and then requires the single-step
	 * to be handled explicitly in the overflow handler to avoid
	 * stepping into the SIGIO handler and getting stuck on the
	 * breakpointed instruction.
	 *
	 * Just disable the test for these architectures until these
	 * issues are resolved.
	 */

Will