linux-kernel - [PATCH v2 4/6] tracing/kprobes: Support perf-style return probe

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Date:   Tue,  1 Sep 2020 16:57:10 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Jonathan Corbet <corbet@....net>
Cc:     mhiramat@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v2 4/6] tracing/kprobes: Support perf-style return probe

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

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_kprobe.c |   21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index aefb6065b508..391361b67c8f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -709,6 +709,18 @@ static inline void sanitize_event_name(char *name)
 			*name = '_';
 }
 
+static inline bool split_return_suffix(char *symbol)
+{
+	char *p = strchr(symbol, '%');
+
+	if (p && !strcmp(p, "%return")) {
+		*p = '\0';
+		return true;
+	}
+
+	return false;
+}
+
 static int trace_kprobe_create(int argc, const char *argv[])
 {
 	/*
@@ -717,6 +729,9 @@ 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
@@ -746,7 +761,6 @@ 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;
@@ -804,12 +818,17 @@ static int trace_kprobe_create(int argc, const char *argv[])
 		symbol = kstrdup(argv[1], GFP_KERNEL);
 		if (!symbol)
 			return -ENOMEM;
+
+		is_return = split_return_suffix(symbol) || is_return;
+
 		/* 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)) {