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

[Masami Hiramatsu]

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 <mhira...@kernel.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)) {