[PATCH 3/3] tools/perf: Fix error reporting

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

If user explicitly specifies a vmlinux or kallsyms file on the command
line and the specified file doesn't yield any symbols, print a warning
message.

	$ perf report -kallsyms
	No kernel symbols in the vmlinux 'allsyms'?
	Failed to load symbols for DSO [kernel.kallsyms], continuing
	without symbols

This could help user better recognize the typo -kallsyms v. --kallsyms.
It would also help if the user points to a stripped/invalid vmlinux or
an invalid kallsyms.

With a stripped vmlinux:

	$ perf report -k /tmp/vmlinux
	No kernel symbols in the vmlinux '/tmp/vmlinux'?
	Failed to load symbols for DSO [kernel.kallsyms], continuing
	without symbols

and with perf top

	$ perf top -k /tmp/vmlinux
	No kernel symbols in the vmlinux '/tmp/vmlinux'?
	/tmp/vmlinux with build id f43f4e78d3afac6492dcae52cd756394247997d6
	not found, continuing without symbols

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
 tools/perf/util/symbol.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 9b66e27..ad5baa4 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1658,8 +1658,13 @@ static int dso__load_kernel_sym(struct dso *dso, struct map *map,
 	}
 
 	if (!symbol_conf.ignore_vmlinux && symbol_conf.vmlinux_name != NULL) {
-		return dso__load_vmlinux(dso, map, symbol_conf.vmlinux_name,
+		nsyms = dso__load_vmlinux(dso, map, symbol_conf.vmlinux_name,
 					 false, filter);
+		if (nsyms <= 0) {
+			pr_warning("No kernel symbols in the vmlinux '%s'?\n",
+					symbol_conf.vmlinux_name);
+		}
+		return nsyms;
 	}
 
 	if (!symbol_conf.ignore_vmlinux && vmlinux_path != NULL) {
@@ -1682,6 +1687,10 @@ do_kallsyms:
 	nsyms = dso__load_kallsyms(dso, kallsyms_filename, map, filter);
 	if (nsyms > 0)
 		pr_debug("Using %s for symbols\n", kallsyms_filename);
+	else if (symbol_conf.kallsyms_name) {
+		pr_warning("No kernel symbols in the kallsyms '%s'?\n",
+				kallsyms_filename);
+	}
 	free(kallsyms_allocated_filename);
 
 	if (nsyms > 0 && !dso__is_kcore(dso)) {
-- 
1.8.3.1