[PATCH -tip v2 6/8] perf-probe: Show appropriate symbol for _stextbased kprobes

[Masami Hiramatsu]

Show appropriate symbol for _stext based kprobes instead
of _stext+offset when perf-probe -l runs without debuginfo.

Without this change:
  # ./perf probe -l
    probe:t_show         (on _stext+889880 with m v)
    probe:t_show_1       (on _stext+928568 with m v t)
    probe:t_show_2       (on _stext+969512 with m v fmt)
    probe:t_show_3       (on _stext+1001416 with m v file)

With this change:
  # ./perf probe -l
    probe:t_show         (on t_show with m v)
    probe:t_show_1       (on t_show with m v t)
    probe:t_show_2       (on t_show with m v fmt)
    probe:t_show_3       (on t_show with m v file)

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
---
 tools/perf/util/probe-event.c |   27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index b35f047..8db172a 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -125,6 +125,11 @@ static struct symbol *__find_kernel_function_by_name(const char *name,
 						     NULL);
 }
 
+static struct symbol *__find_kernel_function(u64 addr, struct map **mapp)
+{
+	return machine__find_kernel_function(host_machine, addr, mapp, NULL);
+}
+
 static struct map *kernel_get_module_map(const char *module)
 {
 	struct rb_node *nd;
@@ -220,12 +225,30 @@ out:
 static int convert_to_perf_probe_point(struct probe_trace_point *tp,
 					struct perf_probe_point *pp)
 {
-	pp->function = strdup(tp->symbol);
+	struct symbol *sym;
+	struct map *map;
+	u64 addr;
+
+	/* _stext based probe point is solved to absolute address */
+	if (tp->symbol && strcmp(tp->symbol, "_stext") == 0) {
+		sym = __find_kernel_function_by_name(tp->symbol, &map);
+		if (!sym)
+			goto failed;
+		addr = map->unmap_ip(map, sym->start + tp->offset);
+		sym = __find_kernel_function(addr, &map);
+		if (!sym)
+			goto failed;
+		pp->function = strdup(sym->name);
+		pp->offset = addr - map->unmap_ip(map, sym->start);
+	} else {
+failed:
+		pp->function = strdup(tp->symbol);
+		pp->offset = tp->offset;
+	}
 
 	if (pp->function == NULL)
 		return -ENOMEM;
 
-	pp->offset = tp->offset;
 	pp->retprobe = tp->retprobe;
 
 	return 0;


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