perf trace: Allow specifying a set of events to add in perfconfig

To add augmented_raw_syscalls to the events speficied by the user, or be
the only one if no events were specified by the user, one can add this
to perfconfig:

  # cat ~/.perfconfig
  [trace]
	  add_events = /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.o
  #

I.e. pre-compile the augmented_raw_syscalls.c BPF program and make it
always load, this way:

  # perf trace -e open* cat /etc/passwd > /dev/null
     0.000 ( 0.013 ms): cat/31557 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC) = 3
     0.035 ( 0.007 ms): cat/31557 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC) = 3
     0.353 ( 0.009 ms): cat/31557 openat(dfd: CWD, filename: /usr/lib/locale/locale-archive, flags: CLOEXEC) = 3
     0.424 ( 0.006 ms): cat/31557 openat(dfd: CWD, filename: /etc/passwd) = 3
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-0lgj7vh64hg3ce44gsmvj7ud@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-config.txt

@@ -521,6 +521,14 @@ diff.*::
 		Possible values are 'delta', 'delta-abs', 'ratio' and
 		'wdiff'.  Default is 'delta'.
 
+trace.*::
+	trace.add_events::
+		Allows adding a set of events to add to the ones specified
+		by the user, or use as a default one if none was specified.
+		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.
+
 SEE ALSO
 --------
 linkperf:perf[1]

tools/perf/builtin-trace.c

@@ -22,6 +22,7 @@
 #include "builtin.h"
 #include "util/cgroup.h"
 #include "util/color.h"
+#include "util/config.h"
 #include "util/debug.h"
 #include "util/env.h"
 #include "util/event.h"
@@ -3523,6 +3524,21 @@ static void trace__set_bpf_map_syscalls(struct trace *trace)
 	trace->syscalls.map = bpf__find_map_by_name("syscalls");
 }
 
+static int trace__config(const char *var, const char *value, void *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);
+	}
+
+	return err;
+}
+
 int cmd_trace(int argc, const char **argv)
 {
 	const char *trace_usage[] = {
@@ -3645,6 +3661,10 @@ int cmd_trace(int argc, const char **argv)
 		goto out;
 	}
 
+	err = perf_config(trace__config, &trace);
+	if (err)
+		goto out;
+
 	argc = parse_options_subcommand(argc, argv, trace_options, trace_subcommands,
 				 trace_usage, PARSE_OPT_STOP_AT_NON_OPTION);