[libbacktrace] Avoid realloc with size == 0 in backtrace_vector_release

As of C17, realloc with size 0 is marked as an obsolescent feature.

Fix this in backtrace_vector_release by using free instead.

Bootstrapped and reg-tested on x86_64.

2018-11-27  Tom de Vries  <tdevries@suse.de>

	* alloc.c (backtrace_vector_release): Handle vec->size == 0 using free
	instead of realloc.
	* Makefile.am (check_PROGRAMS): Add unittest.
	* Makefile.in: Regenerate.
	* unittest.c: New file.

From-SVN: r266504

1 files changed, 12 insertions, 1 deletions

diff --git a/libbacktrace/alloc.c b/libbacktrace/alloc.c
index 7070afb..522b59d 100644
--- a/libbacktrace/alloc.c
+++ b/libbacktrace/alloc.c
@@ -145,12 +145,23 @@ backtrace_vector_release (struct backtrace_state *state ATTRIBUTE_UNUSED,
 			  backtrace_error_callback error_callback,
 			  void *data)
 {
+  vec->alc = 0;
+
+  if (vec->size == 0)
+    {
+      /* As of C17, realloc with size 0 is marked as an obsolescent feature, use
+	 free instead.  */
+      free (vec->base);
+      vec->base = NULL;
+      return 1;
+    }
+
   vec->base = realloc (vec->base, vec->size);
   if (vec->base == NULL)
     {
       error_callback (data, "realloc", errno);
       return 0;
     }
-  vec->alc = 0;
+
   return 1;
 }