Messages in this thread | | | Subject | Re: [PATCH v3] bpf: Remove config check to enable bpf support for branch records | From | Daniel Borkmann <> | Date | Tue, 23 Nov 2021 13:03:43 +0100 |
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On 11/23/21 10:51 AM, Kajol Jain wrote: > Branch data available to bpf programs can be very useful to get > stack traces out of userspace application. > > Commit fff7b64355ea ("bpf: Add bpf_read_branch_records() helper") > added bpf support to capture branch records in x86. Enable this feature > for other architectures as well by removing check specific to x86. > > Incase any architecture doesn't support branch records, > bpf_read_branch_records still have appropriate checks and it > will return error number -EINVAL in that scenario. But based on > documentation there in include/uapi/linux/bpf.h file, incase of > unsupported archs, this function should return -ENOENT. Hence update > the appropriate checks to return -ENOENT instead. > > Selftest 'perf_branches' result on power9 machine which has branch stacks > support. > > Before this patch changes: > [command]# ./test_progs -t perf_branches > #88/1 perf_branches/perf_branches_hw:FAIL > #88/2 perf_branches/perf_branches_no_hw:OK > #88 perf_branches:FAIL > Summary: 0/1 PASSED, 0 SKIPPED, 1 FAILED > > After this patch changes: > [command]# ./test_progs -t perf_branches > #88/1 perf_branches/perf_branches_hw:OK > #88/2 perf_branches/perf_branches_no_hw:OK > #88 perf_branches:OK > Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED > > Selftest 'perf_branches' result on power9 machine which doesn't > have branch stack report. > > After this patch changes: > [command]# ./test_progs -t perf_branches > #88/1 perf_branches/perf_branches_hw:SKIP > #88/2 perf_branches/perf_branches_no_hw:OK > #88 perf_branches:OK > Summary: 1/1 PASSED, 1 SKIPPED, 0 FAILED > > Fixes: fff7b64355eac ("bpf: Add bpf_read_branch_records() helper") > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Kajol Jain <kjain@linux.ibm.com> > --- > > Tested this patch changes on power9 machine using selftest > 'perf branches' which is added in commit 67306f84ca78 ("selftests/bpf: > Add bpf_read_branch_records()") > > Changelog: > v2 -> v3 > - Change the return error number for bpf_read_branch_records > function from -EINVAL to -ENOENT for appropriate checks > as suggested by Daniel Borkmann. > > - Link to the v2 patch: https://lkml.org/lkml/2021/11/18/510 > > v1 -> v2 > - Inorder to add bpf support to capture branch record in > powerpc, rather then adding config for powerpc, entirely > remove config check from bpf_read_branch_records function > as suggested by Peter Zijlstra > > - Link to the v1 patch: https://lkml.org/lkml/2021/11/14/434 > > kernel/trace/bpf_trace.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 7396488793ff..b94a00f92759 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -1402,18 +1402,15 @@ 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 > - return -ENOENT; > -#else > static const u32 br_entry_size = sizeof(struct perf_branch_entry); > struct perf_branch_stack *br_stack = ctx->data->br_stack; > u32 to_copy; > > if (unlikely(flags & ~BPF_F_GET_BRANCH_RECORDS_SIZE)) > - return -EINVAL; > + return -ENOENT;
What's the rationale for also changing the above? Invalid/unsupported flags should still return -EINVAL as they did before ...
> if (unlikely(!br_stack)) > - return -EINVAL; > + return -ENOENT;
... meaning only this one here was necessary.
> if (flags & BPF_F_GET_BRANCH_RECORDS_SIZE) > return br_stack->nr * br_entry_size; > @@ -1425,7 +1422,6 @@ BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx, > memcpy(buf, br_stack->entries, to_copy); > > return to_copy; > -#endif > } > > static const struct bpf_func_proto bpf_read_branch_records_proto = { >
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