[PATCH v2 4/5] perf: kretprobes: offset from reloc_sym if kernel supports it

[Naveen N. Rao]

We indicate support for accepting sym+offset with kretprobes through a
line in ftrace README. Parse the same to identify support and choose the
appropriate format for kprobe_events.

Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
 tools/perf/util/probe-event.c | 47 ++++++++++++++++++++++++++++++++++++-------
 tools/perf/util/probe-event.h |  2 ++
 2 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 35f5b7b7715c..f6bc61c47271 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -737,6 +737,41 @@ post_process_module_probe_trace_events(struct 
probe_trace_event *tevs,
        return ret;
 }
 
+bool is_kretprobe_offset_supported(void)
+{
+       FILE *fp;
+       char *buf = NULL;
+       size_t len = 0;
+       bool target_line = false;
+       static int supported = -1;
+
+       if (supported >= 0)
+               return !!supported;
+
+       if (asprintf(&buf, "%s/README", tracing_path) < 0)
+               return false;
+
+       fp = fopen(buf, "r");
+       if (!fp)
+               goto end;
+
+       zfree(&buf);
+       while (getline(&buf, &len, fp) > 0) {
+               target_line = !!strstr(buf, "place (kretprobe): ");
+               if (!target_line)
+                       continue;
+               supported = 1;
+       }
+       if (supported == -1)
+               supported = 0;
+
+       fclose(fp);
+end:
+       free(buf);
+
+       return !!supported;
+}
+
 static int
 post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
                                       int ntevs)
@@ -757,7 +792,9 @@ post_process_kernel_probe_trace_events(struct 
probe_trace_event *tevs,
        }
 
        for (i = 0; i < ntevs; i++) {
-               if (!tevs[i].point.address || tevs[i].point.retprobe)
+               if (!tevs[i].point.address)
+                       continue;
+               if (tevs[i].point.retprobe && !is_kretprobe_offset_supported())
                        continue;
                /* If we found a wrong one, mark it by NULL symbol */
                if (kprobe_warn_out_range(tevs[i].point.symbol,
@@ -1528,11 +1565,6 @@ static int parse_perf_probe_point(char *arg, struct 
perf_probe_event *pev)
                return -EINVAL;
        }
 
-       if (pp->retprobe && !pp->function) {
-               semantic_error("Return probe requires an entry function.\n");
-               return -EINVAL;
-       }
-
        if ((pp->offset || pp->line || pp->lazy_line) && pp->retprobe) {
                semantic_error("Offset/Line/Lazy pattern can't be used with "
                               "return probe.\n");
@@ -2841,7 +2873,8 @@ static int find_probe_trace_events_from_map(struct 
perf_probe_event *pev,
        }
 
        /* Note that the symbols in the kmodule are not relocated */
-       if (!pev->uprobes && !pp->retprobe && !pev->target) {
+       if (!pev->uprobes && !pev->target &&
+                       (!pp->retprobe || is_kretprobe_offset_supported())) {
                reloc_sym = kernel_get_ref_reloc_sym();
                if (!reloc_sym) {
                        pr_warning("Relocated base symbol is not found!\n");
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 5d4e94061402..449d4f311355 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -135,6 +135,8 @@ bool perf_probe_with_var(struct perf_probe_event *pev);
 /* Check the perf_probe_event needs debuginfo */
 bool perf_probe_event_need_dwarf(struct perf_probe_event *pev);
 
+bool is_kretprobe_offset_supported(void);
+
 /* Release event contents */
 void clear_perf_probe_event(struct perf_probe_event *pev);
 void clear_probe_trace_event(struct probe_trace_event *tev);
-- 
2.11.0