[PATCH perf/core v2 4/4] perf-probe: Find probe events without target module

[Masami Hiramatsu]

Find probe events without -m "module" option. If perf-probe
failed to find given function in kernel image, it tries to
find same symbol and module in kallsyms, and retry search
in the found module. E.g.

  # perf probe -D i915_capabilities
  p:probe/i915_capabilities i915:i915_capabilities+0

Note: without -m option, perf probe can not find inlined
function since there is no symbol information in kallsyms.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Suggested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
  Changes in v2:
   - Fix to remove unneeded zero-return.
   - Remove unneeded debug message.
---
 tools/perf/util/probe-event.c |   69 ++++++++++++++++++++++++++++++-----------
 1 file changed, 51 insertions(+), 18 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 6a6f44d..715f330 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -858,11 +858,7 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
 
 	debuginfo__delete(dinfo);
 
-	if (ntevs == 0)	{	/* No error but failed to find probe point. */
-		pr_warning("Probe point '%s' not found.\n",
-			   synthesize_perf_probe_point(&pev->point));
-		return -ENOENT;
-	} else if (ntevs < 0) {
+	if (ntevs < 0) {
 		/* Error path : ntevs < 0 */
 		pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs);
 		if (ntevs == -EBADF)
@@ -2829,9 +2825,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
 	 */
 	num_matched_functions = find_probe_functions(map, pp->function, syms);
 	if (num_matched_functions == 0) {
-		pr_err("Failed to find symbol %s in %s\n", pp->function,
-			pev->target ? : "kernel");
-		ret = -ENOENT;
+		ret = 0;
 		goto out;
 	} else if (num_matched_functions > probe_conf.max_probes) {
 		pr_err("Too many functions matched in %s\n",
@@ -3233,6 +3227,42 @@ static int find_probe_trace_events_from_cache(struct perf_probe_event *pev,
 	return ret;
 }
 
+static int __convert_to_probe_trace_events(struct perf_probe_event *pev,
+					   struct probe_trace_event **tevs)
+{
+	int ret;
+
+	/* At first, we need to lookup cache entry */
+	ret = find_probe_trace_events_from_cache(pev, tevs);
+	if (ret > 0 || pev->sdt)	/* SDT can be found only in the cache */
+		return ret == 0 ? -ENOENT : ret; /* Found in probe cache */
+
+	/* Convert perf_probe_event with debuginfo */
+	ret = try_to_find_probe_trace_events(pev, tevs);
+	if (ret != 0)
+		return ret;	/* Found in debuginfo or got an error */
+
+	return find_probe_trace_events_from_map(pev, tevs);
+}
+
+static char *find_module_from_kallsyms(const char *symbol_name)
+{
+	struct machine *machine = machine__new_kallsyms();
+	struct symbol *sym;
+	struct map *map;
+	char *module;
+
+	sym = machine__find_kernel_function_by_name(machine, symbol_name, &map);
+	if (!sym || map->dso->short_name[0] != '[')
+		return NULL;
+	pr_debug("Found %s in %s\n", sym->name, map->dso->short_name);
+	module = strdup(map->dso->short_name + 1);
+	if (module)
+		module[strlen(module) - 1] = '\0';
+
+	return module;
+}
+
 static int convert_to_probe_trace_events(struct perf_probe_event *pev,
 					 struct probe_trace_event **tevs)
 {
@@ -3255,17 +3285,20 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
 	if (ret > 0)
 		return ret;
 
-	/* At first, we need to lookup cache entry */
-	ret = find_probe_trace_events_from_cache(pev, tevs);
-	if (ret > 0 || pev->sdt)	/* SDT can be found only in the cache */
-		return ret == 0 ? -ENOENT : ret; /* Found in probe cache */
-
-	/* Convert perf_probe_event with debuginfo */
-	ret = try_to_find_probe_trace_events(pev, tevs);
-	if (ret != 0)
-		return ret;	/* Found in debuginfo or got an error */
+	ret = __convert_to_probe_trace_events(pev, tevs);
+	/* Not found. will retry to check kmodule if possible */
+	if (ret == 0 && !pev->uprobes && !pev->target) {
+		pev->target = find_module_from_kallsyms(pev->point.function);
+		if (pev->target)
+			ret = __convert_to_probe_trace_events(pev, tevs);
+	}
 
-	return find_probe_trace_events_from_map(pev, tevs);
+	if (ret == 0) {
+		pr_warning("Probe point '%s' not found.\n",
+			   synthesize_perf_probe_point(&pev->point));
+		ret = -ENOENT;
+	}
+	return ret;
 }
 
 int convert_perf_probe_events(struct perf_probe_event *pevs, int npevs)