GCC 13 realloc warning fix for bctbx_concat/belle_sip_concat

[fweimer-rh]

Context

We package belle-sip in Fedora. We have an older version which does not use the split bctoolbox yet.

General information

Fedora 38

Expected behaviour

Package builds with GCC 13.

To Reproduce

Build the software with GCC 13.

belle_sip_utils.c: In function 'belle_sip_concat':
belle_sip_utils.c:555:31: error: pointer 'result_71' may be used after 'realloc' [-Werror=use-after-free]
  555 |               wp = newp + (wp - result);
      |                           ~~~~^~~~~~~~~
belle_sip_utils.c:549:31: note: call to 'realloc' here
  549 |               newp = (char *) realloc (result, allocated);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Additional context

This seems to fix it:

diff --git a/src/belle_sip_utils.c b/src/belle_sip_utils.c
index 9688a2b..51ec3e9 100644
--- a/src/belle_sip_utils.c
+++ b/src/belle_sip_utils.c
@@ -545,6 +545,7 @@ char * belle_sip_concat (const char *str, ...) {
           /* Resize the allocated memory if necessary.  */
           if (wp + len + 1 > result + allocated)
             {
+             ptrdiff_t wp_offset = wp - result;
               allocated = (allocated + len) * 2;
               newp = (char *) realloc (result, allocated);
               if (newp == NULL)
@@ -552,7 +553,7 @@ char * belle_sip_concat (const char *str, ...) {
                   free (result);
                   return NULL;
                 }
-              wp = newp + (wp - result);
+              wp = newp + wp_offset;
               result = newp;
             }
           memcpy (wp, s, len);

A similar patch is apparently needed for bctoolbox.

SDK logs URL

No response