From: Leo Yan leo.yan@linaro.org
[ Upstream commit 6a5f3d94cb69a185b921cb92c39888dc31009acb ]
As there are 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 we 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 [1]: "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' [2]; 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.
[1] https://lkml.org/lkml/2018/11/15/205 [2] https://lkml.org/lkml/2015/12/23/477
Signed-off-by: Leo Yan leo.yan@linaro.org Cc: Adrian Hunter adrian.hunter@intel.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Brajeswar Ghosh brajeswar.linux@gmail.com Cc: Florian Fainelli f.fainelli@gmail.com Cc: Jiri Olsa jolsa@redhat.com Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Petlan mpetlan@redhat.com Cc: Namhyung Kim namhyung@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Song Liu songliubraving@fb.com Cc: Souptick Joarder jrdr.linux@gmail.com Cc: Will Deacon will@kernel.org Link: http://lore.kernel.org/lkml/20191018085531.6348-3-leo.yan@linaro.org Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 910e25e64188..6cf00650602e 100644 --- a/tools/perf/tests/bp_signal.c +++ b/tools/perf/tests/bp_signal.c @@ -48,14 +48,6 @@ asm ( "__test_function:\n" "incq (%rdi)\n" "ret\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"); - #else static void __test_function(volatile long *ptr) { @@ -301,10 +293,15 @@ 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; #else return true;