Re: [PATCH v1 3/3] perf tests: Disable bp_signal testing for arm64
From: Arnaldo Carvalho de Melo
Date: Fri Oct 18 2019 - 13:59:27 EST
Em Fri, Oct 18, 2019 at 04:55:31PM +0800, Leo Yan escreveu:
> As there have several discussions for enabling Perf breakpoint signal
> testing on arm64 platform; arm64 needs to rely on single-step to execute
> the breakpointed instruction and then reinstall the breakpoint exception
> handler. But if hook the breakpoint with a signal, the signal handler
> will do the stepping rather than the breakpointed instruction, this
> causes infinite loops as below:
> Kernel space | Userspace
> | __test_function() -> hit
> | breakpoint
> breakpoint_handler() |
> `-> user_enable_single_step() |
> do_signal() |
> | sig_handler() -> Step one
> | instruction and
> | trap to kernel
> single_step_handler() |
> `-> reinstall_suspended_bps() |
> | __test_function() -> hit
> | breakpoint again and
> | repeat up flow infinitely
> As Will Deacon mentioned : "that we require the overflow handler to
> do the stepping on arm/arm64, which is relied upon by GDB/ptrace. The
> hw_breakpoint code is a complete disaster so my preference would be to
> rip out the perf part and just implement something directly in ptrace,
> but it's a pretty horrible job". Though Will commented this on arm
> architecture, but the comment also can apply on arm64 architecture.
> For complete information, I searched online and found a few years back,
> Wang Nan sent one patch 'arm64: Store breakpoint single step state into
> pstate' ; the patch tried to resolve this issue by avoiding single
> stepping in signal handler and defer to enable the signal stepping when
> return to __test_function(). The fixing was not merged due to the
> concern for missing to handle different usage cases.
> Based on the info, the most feasible way is to skip Perf breakpoint
> signal testing for arm64 and this could avoid the duplicate
> investigation efforts when people see the failure. This patch skips
> this case on arm64 platform, which is same with arm architecture.
>  https://lkml.org/lkml/2018/11/15/205
>  https://lkml.org/lkml/2015/12/23/477
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> tools/perf/tests/bp_signal.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
> diff --git a/tools/perf/tests/bp_signal.c b/tools/perf/tests/bp_signal.c
> index c1c2c13de254..166f411568a5 100644
> --- a/tools/perf/tests/bp_signal.c
> +++ b/tools/perf/tests/bp_signal.c
> @@ -49,14 +49,6 @@ asm (
> "incq (%rdi)\n"
> -#elif defined (__aarch64__)
> -extern void __test_function(volatile long *ptr);
> -asm (
> - ".globl __test_function\n"
> - "__test_function:\n"
> - "str x30, [x0]\n"
> - "ret\n");
> static void __test_function(volatile long *ptr)
> @@ -302,10 +294,15 @@ bool test__bp_signal_is_supported(void)
> * stepping into the SIGIO handler and getting stuck on the
> * breakpointed instruction.
> + * Since arm64 has the same issue with arm for the single-step
> + * handling, this case also gets suck on the breakpointed
> + * instruction.
> + *
> * Just disable the test for these architectures until these
> * issues are resolved.
> -#if defined(__powerpc__) || defined(__s390x__) || defined(__arm__)
> +#if defined(__powerpc__) || defined(__s390x__) || defined(__arm__) || \
> + defined(__aarch64__)
> return false;
> return true;