Re: [PATCH 2/6] bpf: Add bpf_perf_event_output_kfunc

On Tue, Jan 21, 2020 at 04:03:23PM -0800, Alexei Starovoitov wrote:

On Tue, Jan 21, 2020 at 01:05:08PM +0100, Jiri Olsa wrote:

quoted

Adding support to use perf_event_output in
BPF_TRACE_FENTRY/BPF_TRACE_FEXIT programs.

Using nesting regs array from raw tracepoint helpers.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/trace/bpf_trace.c | 41 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 19e793aa441a..6a18e2ae6e30 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -1172,6 +1172,43 @@ raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	}
 }
 
+BPF_CALL_5(bpf_perf_event_output_kfunc, void *, ctx, struct bpf_map *, map,
+	   u64, flags, void *, data, u64, size)
+{
+	struct pt_regs *regs = get_bpf_raw_tp_regs();
+	int ret;
+
+	if (IS_ERR(regs))
+		return PTR_ERR(regs);
+
+	perf_fetch_caller_regs(regs);
+	ret = ____bpf_perf_event_output(regs, map, flags, data, size);
+	put_bpf_raw_tp_regs();
+	return ret;
+}

I'm not sure why copy paste bpf_perf_event_output_raw_tp() into new function.

quoted

@@ -1181,6 +1218,10 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_skb_output_proto;
 #endif
 	default:
+		if (prog->expected_attach_type == BPF_TRACE_FENTRY ||
+		    prog->expected_attach_type == BPF_TRACE_FEXIT)
+			return kfunc_prog_func_proto(func_id, prog);
+
 		return raw_tp_prog_func_proto(func_id, prog);

Are you saying bpf_perf_event_output_raw_tp() for some reason
didn't work for fentry/fexit?
But above is exact copy-paste and it somehow worked?

Ditto for patches 3,4.

ugh right.. did not realize that after switching to the rawtp
regs nest arrays it's identical and we don't need that

jirka