linux-kernel - Re: [PATCH v2 09/10] perf trace: Collect augmented data using BPF

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Message-ID: <ZsiQyahfNYCAmbZq@x1>
Date: Fri, 23 Aug 2024 10:38:17 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: adrian.hunter@...el.com, irogers@...gle.com, jolsa@...nel.org,
	kan.liang@...ux.intel.com, namhyung@...nel.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/10] perf trace: Collect augmented data using BPF

On Fri, Aug 23, 2024 at 10:24:09AM -0300, Arnaldo Carvalho de Melo wrote:
> On Thu, Aug 15, 2024 at 09:36:25AM +0800, Howard Chu wrote:
> > +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > @@ -427,7 +538,8 @@ int sys_enter(struct syscall_enter_args *args)
> >  	 * "!raw_syscalls:unaugmented" that will just return 1 to return the
> >  	 * unaugmented tracepoint payload.
> >  	 */
> > -	bpf_tail_call(args, &syscalls_sys_enter, augmented_args->args.syscall_nr);
> > +	if (augment_sys_enter(args, &augmented_args->args))
> > +		bpf_tail_call(args, &syscalls_sys_enter, augmented_args->args.syscall_nr);
> 
> We shouldn't do that, instead we keep doing
> 
> 	bpf_tail_call(args, &syscalls_sys_enter, augmented_args->args.syscall_nr);
> 
> And userspace will setup the syscalls_sys_enter map adding the generic
> pointer collector (augment_sys_enter) for syscalls that have pointers
> _and_ are not serviced by a pre-existing, specialized handler, this way
> we keep the ones we have already and that already take into account
> pretty printing network addresses based on the network family, knows how
> to pretty print flags (the perf_event_open, etc).
> 
> I'll try to do this now.

So, step by step, first this, and then hook it to the syscalls that:

1) have a pointer to collect and no handler, i.e. as a last step in
assigning the functions to be tail called from the syscalls BPF map.

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 37ca96e130a5862d..a909880bd25e51d1 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1007,9 +1007,11 @@ static size_t btf_enum_scnprintf(const struct btf_type *type, struct btf *btf, c
 	return 0;
 }
 
-static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg_fmt *arg_fmt, char *bf,
+static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg *arg, char *bf,
 				   size_t size, int val, char *type)
 {
+	struct syscall_arg_fmt *arg_fmt = arg->fmt;
+
 	if (trace->btf == NULL)
 		return 0;
 
@@ -1029,7 +1031,7 @@ static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg_fmt *
 }
 
 #else // HAVE_LIBBPF_SUPPORT
-static size_t trace__btf_scnprintf(struct trace *trace __maybe_unused, struct syscall_arg_fmt *arg_fmt __maybe_unused,
+static size_t trace__btf_scnprintf(struct trace *trace __maybe_unused, struct syscall_arg *arg __maybe_unused,
 				   char *bf __maybe_unused, size_t size __maybe_unused, int val __maybe_unused,
 				   char *type __maybe_unused)
 {
@@ -2284,7 +2286,7 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 			if (trace->show_arg_names)
 				printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
 
-			btf_printed = trace__btf_scnprintf(trace, &sc->arg_fmt[arg.idx], bf + printed,
+			btf_printed = trace__btf_scnprintf(trace, &arg, bf + printed,
 							   size - printed, val, field->type);
 			if (btf_printed) {
 				printed += btf_printed;
@@ -2987,7 +2989,7 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct evsel *evsel,
 		if (trace->show_arg_names)
 			printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
 
-		btf_printed = trace__btf_scnprintf(trace, arg, bf + printed, size - printed, val, field->type);
+		btf_printed = trace__btf_scnprintf(trace, &syscall_arg, bf + printed, size - printed, val, field->type);
 		if (btf_printed) {
 			printed += btf_printed;
 			continue;