perf report: Allow user to specify path to kallsyms file

This is useful for analyzing a perf data file on a different system than
the one data was collected on and still include symbols from loaded
kernel modules in the output.

Commiter note: Updated the man page accordingly.

LKML-Reference: <1291775986-16475-1-git-send-email-daahern@cisco.com>
Signed-off-by: David Ahern <daahern@cisco.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-report.txt

@@ -104,6 +104,9 @@ OPTIONS
 --vmlinux=<file>::
         vmlinux pathname
 
+--kallsyms=<file>::
+        kallsyms pathname
+
 -m::
 --modules::
         Load module symbols. WARNING: This should only be used with -k and

tools/perf/builtin-report.c

@@ -443,6 +443,8 @@ static const struct option options[] = {
 		    "dump raw trace in ASCII"),
 	OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,
 		   "file", "vmlinux pathname"),
+	OPT_STRING(0, "kallsyms", &symbol_conf.kallsyms_name,
+		   "file", "kallsyms pathname"),
 	OPT_BOOLEAN('f', "force", &force, "don't complain, do it"),
 	OPT_BOOLEAN('m', "modules", &symbol_conf.use_modules,
 		    "load module symbols - WARNING: use only with -k and LIVE kernel"),

tools/perf/util/symbol.c

@@ -1830,8 +1830,8 @@ static int dso__load_kernel_sym(struct dso *self, struct map *map,
 	const char *kallsyms_filename = NULL;
 	char *kallsyms_allocated_filename = NULL;
 	/*
-	 * Step 1: if the user specified a vmlinux filename, use it and only
-	 * it, reporting errors to the user if it cannot be used.
+	 * 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.
 	 *
 	 * For instance, try to analyse an ARM perf.data file _without_ a
 	 * build-id, or if the user specifies the wrong path to the right
@@ -1844,6 +1844,11 @@ static int dso__load_kernel_sym(struct dso *self, struct map *map,
 	 * validation in dso__load_vmlinux and will bail out if they don't
 	 * match.
 	 */
+	if (symbol_conf.kallsyms_name != NULL) {
+		kallsyms_filename = symbol_conf.kallsyms_name;
+		goto do_kallsyms;
+	}
+
 	if (symbol_conf.vmlinux_name != NULL) {
 		err = dso__load_vmlinux(self, map,
 					symbol_conf.vmlinux_name, filter);

tools/perf/util/symbol.h

@@ -72,6 +72,7 @@ struct symbol_conf {
 			show_cpu_utilization,
 			initialized;
 	const char	*vmlinux_name,
+			*kallsyms_name,
 			*source_prefix,
 			*field_sep;
 	const char	*default_guest_vmlinux_name,