tracing/kprobes: Support perf-style return probe

Support perf-style return probe ("SYMBOL%return") for kprobe events.
This will allow boot-time tracing user to define a return probe event.

Link: https://lkml.kernel.org/r/159972813535.428528.4437029657208468954.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -718,6 +718,9 @@ static int trace_kprobe_create(int argc, const char *argv[])
 	 *      p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
 	 *  - Add kretprobe:
 	 *      r[MAXACTIVE][:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
+	 *    Or
+	 *      p:[GRP/]EVENT] [MOD:]KSYM[+0]%return [FETCHARGS]
+	 *
 	 * Fetch args:
 	 *  $retval	: fetch return value
 	 *  $stack	: fetch stack address
@@ -747,7 +750,6 @@ static int trace_kprobe_create(int argc, const char *argv[])
 	switch (argv[0][0]) {
 	case 'r':
 		is_return = true;
-		flags |= TPARG_FL_RETURN;
 		break;
 	case 'p':
 		break;
@@ -805,12 +807,26 @@ static int trace_kprobe_create(int argc, const char *argv[])
 		symbol = kstrdup(argv[1], GFP_KERNEL);
 		if (!symbol)
 			return -ENOMEM;
+
+		tmp = strchr(symbol, '%');
+		if (tmp) {
+			if (!strcmp(tmp, "%return")) {
+				*tmp = '\0';
+				is_return = true;
+			} else {
+				trace_probe_log_err(tmp - symbol, BAD_ADDR_SUFFIX);
+				goto parse_error;
+			}
+		}
+
 		/* TODO: support .init module functions */
 		ret = traceprobe_split_symbol_offset(symbol, &offset);
 		if (ret || offset < 0 || offset > UINT_MAX) {
 			trace_probe_log_err(0, BAD_PROBE_ADDR);
 			goto parse_error;
 		}
+		if (is_return)
+			flags |= TPARG_FL_RETURN;
 		if (kprobe_on_func_entry(NULL, symbol, offset))
 			flags |= TPARG_FL_FENTRY;
 		if (offset && is_return && !(flags & TPARG_FL_FENTRY)) {