perf trace: Allow configuring if zeroed syscall args should be printed

The default so far, since we show argument names followed by its values,
was to make the output more compact by suppressing most zeroed args.

Make this configurable so that users can choose what best suit their
needs.

Cc: Adrian Hunter <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Luis Cláudio Gonçalves <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Link: https://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/Documentation/perf-config.txt

@@ -528,6 +528,8 @@ trace.*::
 		The initial use case is to add augmented_raw_syscalls.o to
 		activate the 'perf trace' logic that looks for syscall
 		pointer contents after the normal tracepoint payload.
+	trace.show_zeros::
+		Do not suppress syscall arguments that are equal to zero.
 
 SEE ALSO
 --------

tools/perf/builtin-trace.c

@@ -127,6 +127,7 @@ struct trace {
 	bool			show_tool_stats;
 	bool			trace_syscalls;
 	bool			kernel_syscallchains;
+	bool			show_zeros;
 	bool			force;
 	bool			vfs_getname;
 	int			trace_pgfaults;
@@ -1598,6 +1599,7 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
  			 * strarray for it.
  			 */
 			if (val == 0 &&
+			    !trace->show_zeros &&
 			    !(sc->arg_fmt &&
 			      (sc->arg_fmt[arg.idx].show_zero ||
 			       sc->arg_fmt[arg.idx].scnprintf == SCA_STRARRAY ||
@@ -3526,14 +3528,16 @@ static void trace__set_bpf_map_syscalls(struct trace *trace)
 
 static int trace__config(const char *var, const char *value, void *arg)
 {
+	struct trace *trace = arg;
 	int err = 0;
 
 	if (!strcmp(var, "trace.add_events")) {
-		struct trace *trace = arg;
 		struct option o = OPT_CALLBACK('e', "event", &trace->evlist, "event",
 					       "event selector. use 'perf list' to list available events",
 					       parse_events_option);
 		err = parse_events_option(&o, value, 0);
+	} else if (!strcmp(var, "trace.show_zeros")) {
+		trace->show_zeros = perf_config_bool(var, value);
 	}
 
 	return err;