Re: N3322 functionality tests

Lasse Collin wrote on 2026-08-03:
> (Actually, memmove(NULL, ptr, 0) executes ptr <
> NULL, which is still undefined. It's an obsolete module though.)

Fixing it like this:


2026-08-15  Bruno Haible  <[email protected]>

	memmove: Avoid undefined behaviour upon memmove (NULL, ptr, 0).
	Reported by Lasse Collin in
	<https://lists.gnu.org/archive/html/bug-gnulib/2026-08/msg00096.html>.
	* lib/memmove.c (memmove): Test for length==0 case early.

diff --git a/lib/memmove.c b/lib/memmove.c
index 0d80de69c2..e7b17f6335 100644
--- a/lib/memmove.c
+++ b/lib/memmove.c
@@ -12,17 +12,26 @@
 void *
 memmove (void *dest0, void const *source0, size_t length)
 {
-  char *dest = dest0;
-  char const *source = source0;
-  if (source < dest)
-    /* Moving from low mem to hi mem; start at end.  */
-    for (source += length, dest += length; length; --length)
-      *--dest = *--source;
-  else if (source != dest)
+  if (length > 0)
     {
-      /* Moving from hi mem to low mem; start at beginning.  */
-      for (; length; --length)
-        *dest++ = *source++;
+      char *dest = dest0;
+      char const *source = source0;
+      if (source < dest)
+        {
+          /* Moving from low mem to hi mem; start at end.  */
+          source += length;
+          dest += length;
+          do
+            *--dest = *--source;
+          while (--length > 0);
+        }
+      else if (source != dest)
+        {
+          /* Moving from hi mem to low mem; start at beginning.  */
+          do
+            *dest++ = *source++;
+          while (--length > 0);
+        }
     }
   return dest0;
 }