perf symbols: Try to load vmlinux from buildid database

Currently we don't check on kernel's vmlinux the same way as we do for
normal binaries, but we either look for kallsyms file in build id
database or check on known vmlinux locations (plus some other optional
paths).

This patch adds the check for standard build id binary location, so we
are ready once we start to store it there from debuginfod in following
changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201126170026.2619053-13-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/build-id.c

@@ -261,10 +261,9 @@ static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso,
 	    "debug" : "elf"));
 }
 
-char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
-			     bool is_debug)
+char *__dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
+			       bool is_debug, bool is_kallsyms)
 {
-	bool is_kallsyms = dso__is_kallsyms((struct dso *)dso);
 	bool is_vdso = dso__is_vdso((struct dso *)dso);
 	char sbuild_id[SBUILD_ID_SIZE];
 	char *linkname;
@@ -293,6 +292,14 @@ char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
 	return bf;
 }
 
+char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
+			     bool is_debug)
+{
+	bool is_kallsyms = dso__is_kallsyms((struct dso *)dso);
+
+	return __dso__build_id_filename(dso, bf, size, is_debug, is_kallsyms);
+}
+
 #define dsos__for_each_with_build_id(pos, head)	\
 	list_for_each_entry(pos, head, node)	\
 		if (!pos->has_build_id)		\

tools/perf/util/build-id.h

@@ -29,6 +29,8 @@ char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
 
 char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
 			     bool is_debug);
+char *__dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
+			       bool is_debug, bool is_kallsyms);
 
 int build_id__mark_dso_hit(struct perf_tool *tool, union perf_event *event,
 			   struct perf_sample *sample, struct evsel *evsel,

tools/perf/util/symbol.c

@@ -2189,6 +2189,8 @@ static int dso__load_kernel_sym(struct dso *dso, struct map *map)
 	int err;
 	const char *kallsyms_filename = NULL;
 	char *kallsyms_allocated_filename = NULL;
+	char *filename = NULL;
+
 	/*
 	 * Step 1: if the user specified a kallsyms or vmlinux filename, use
 	 * it and only it, reporting errors to the user if it cannot be used.
@@ -2213,6 +2215,20 @@ static int dso__load_kernel_sym(struct dso *dso, struct map *map)
 		return dso__load_vmlinux(dso, map, symbol_conf.vmlinux_name, false);
 	}
 
+	/*
+	 * Before checking on common vmlinux locations, check if it's
+	 * stored as standard build id binary (not kallsyms) under
+	 * .debug cache.
+	 */
+	if (!symbol_conf.ignore_vmlinux_buildid)
+		filename = __dso__build_id_filename(dso, NULL, 0, false, false);
+	if (filename != NULL) {
+		err = dso__load_vmlinux(dso, map, filename, true);
+		if (err > 0)
+			return err;
+		free(filename);
+	}
+
 	if (!symbol_conf.ignore_vmlinux && vmlinux_path != NULL) {
 		err = dso__load_vmlinux_path(dso, map);
 		if (err > 0)