[COMMITTED] tests: Don't printf a known NULL symname.

[Mark Wielaard]

GCC9 on 32bit systems might warn about '%s' directive argument is null
for symname in backtrace.c. Just check whether symname is NULL.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 tests/ChangeLog   | 4 ++++
 tests/backtrace.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/tests/ChangeLog b/tests/ChangeLog
index 71aa178..a4f5dd3 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,7 @@
+2019-04-30  Mark Wielaard  <m...@klomp.org>
+
+       * backtrace.c (frame_callback): Explicitly check symname is NULL.
+
 2019-03-04  Mark Wielaard  <m...@klomp.org>
 
        * backtrace.c (tgkill): Remove define.
diff --git a/tests/backtrace.c b/tests/backtrace.c
index ecf5583..36c8b8c 100644
--- a/tests/backtrace.c
+++ b/tests/backtrace.c
@@ -185,7 +185,7 @@ frame_callback (Dwfl_Frame *state, void *frame_arg)
     symname = dwfl_module_addrname (mod, pc_adjusted);
 
   printf ("#%2d %#" PRIx64 "%4s\t%s\n", *framenop, (uint64_t) pc,
-         ! isactivation ? "- 1" : "", symname);
+         ! isactivation ? "- 1" : "", symname ?: "<null>");
   pid_t tid = dwfl_thread_tid (thread);
   callback_verify (tid, *framenop, pc, symname, dwfl);
   (*framenop)++;
-- 
1.8.3.1