[PATCH] perf: report: don't call map__kmap if map is NULL.

[Wang Nan <wangnan0@huawei.com>]

report__warn_kptr_restrict() calls map__kmap(kernel_map) before
checking kernel_map againest NULL. Which is dangerous, since
map__kmap() will return a invalid and not NULL address. It will trigger
a warning message in map__kmap() after patch "perf: kmaps: enforce
usage of kmaps to protect futher bugs."

This patch fixes it by adding the missing checking.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
 tools/perf/builtin-report.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index b5b2ad4..476cdf7 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -347,7 +347,7 @@ static int perf_evlist__tty_browse_hists(struct perf_evlist *evlist,
 static void report__warn_kptr_restrict(const struct report *rep)
 {
 	struct map *kernel_map = rep->session->machines.host.vmlinux_maps[MAP__FUNCTION];
-	struct kmap *kernel_kmap = map__kmap(kernel_map);
+	struct kmap *kernel_kmap = kernel_map ? map__kmap(kernel_map) : NULL;
 
 	if (kernel_map == NULL ||
 	    (kernel_map->dso->hit &&
-- 
1.8.3.4