[PATCH] perf report: Add warning when libunwind not compiled in

[Jin Yao]

We received a user report that call-graph dwarf mode was enabled in perf
record but perf report didn't unwind the callstack correctly. The reason was,
libunwind was not compiled in.

We can use 'perf -vv' to check the compiled libraries but it would be valuable
to report a warning to user directly (especially valuable for perf newbie).

The warning is,

Warning:
Please install libunwind development packages during the perf build.

Both tui and stdio are supported.

Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
 tools/perf/builtin-report.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index aae0e57c60fb..7accaf8ef689 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -399,6 +399,13 @@ static int report__setup_sample_type(struct report *rep)
 				PERF_SAMPLE_BRANCH_ANY))
 		rep->nonany_branch_mode = true;
 
+#ifndef HAVE_LIBUNWIND_SUPPORT
+	if (dwarf_callchain_users) {
+		ui__warning("Please install libunwind development packages "
+			    "during the perf build.\n");
+	}
+#endif
+
 	return 0;
 }
 
-- 
2.17.1