On 11/15/21 5:44 AM, Kajol Jain wrote:
Branch data available to bpf programs can be very useful to get stack traces out of userspace applications. Commit fff7b64355ea ("bpf: Add bpf_read_branch_records() helper") added bpf support to capture branch records in x86. Enable this feature for powerpc as well. Commit 67306f84ca78 ("selftests/bpf: Add bpf_read_branch_records() selftest") adds selftest corresponding to bpf branch read function bpf_read_branch_records(). Used this selftest to test bpf support, for reading branch records in powerpc. Selftest result in power9 box before this patch changes: [command]# ./test_progs -t perf_branches Failed to load bpf_testmod.ko into the kernel: -8 WARNING! Selftests relying on bpf_testmod.ko will be skipped. test_perf_branches_common:PASS:test_perf_branches_load 0 nsec test_perf_branches_common:PASS:attach_perf_event 0 nsec test_perf_branches_common:PASS:set_affinity 0 nsec check_good_sample:PASS:output not valid 0 nsec check_good_sample:FAIL:read_branches_size err -2 check_good_sample:FAIL:read_branches_stack err -2 check_good_sample:FAIL:read_branches_stack stack bytes written=-2 not multiple of struct size=24 check_good_sample:FAIL:read_branches_global err -2 check_good_sample:FAIL:read_branches_global global bytes written=-2 not multiple of struct size=24 check_good_sample:PASS:read_branches_size 0 nsec #75/1 perf_branches_hw:FAIL #75/2 perf_branches_no_hw:OK #75 perf_branches:FAIL Summary: 0/1 PASSED, 0 SKIPPED, 2 FAILED Selftest result in power9 box after this patch changes: [command]#: ./test_progs -t perf_branches #75/1 perf_branches_hw:OK #75/2 perf_branches_no_hw:OK #75 perf_branches:OK Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED Signed-off-by: Kajol Jain<kjain@xxxxxxxxxxxxx> --- kernel/trace/bpf_trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index fdd14072fc3b..2b7343b64bb7 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1245,7 +1245,7 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto = { BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx, void *, buf, u32, size, u64, flags) { -#ifndef CONFIG_X86 +#if !(defined(CONFIG_X86) || defined(CONFIG_PPC64))
Can this really be enabled generically? Looking at 3925f46bb590 ("powerpc/perf: Enable branch stack sampling framework") it says POWER8 [and beyond]. Should there be a generic Kconfig symbol like ARCH_HAS_BRANCH_RECORDS that can be selected by archs instead?
return -ENOENT; #else static const u32 br_entry_size = sizeof(struct perf_branch_entry);