reallocarray: don’t crash if item size is 0

This problem affects only platforms where xalloc_oversized
divides a number by the size arg.  Fix this by defining
xalloc_oversized (n, s) to work even if s == 0.
* lib/malloca.h, lib/xalloc-oversized.h: Document new behavior.
* lib/xalloc-oversized.h (__xalloc_oversized): Do not crash if S==0.
* tests/test-reallocarray.c (main): Test for the bug.

1 files changed, 7 insertions, 2 deletions

diff --git a/tests/test-reallocarray.c b/tests/test-reallocarray.c
index 973f22ba66..6de355e6bd 100644
--- a/tests/test-reallocarray.c
+++ b/tests/test-reallocarray.c
@@ -26,12 +26,12 @@ SIGNATURE_CHECK (reallocarray, void *, (void *, size_t, size_t));
 int
 main ()
 {
-  void *volatile p = NULL;
-
   /* Check that reallocarray fails when requested to allocate a block
      of memory larger than PTRDIFF_MAX or SIZE_MAX bytes.  */
   for (size_t n = 2; n != 0; n <<= 1)
     {
+      void *volatile p = NULL;
+
       p = reallocarray (p, PTRDIFF_MAX / n + 1, n);
       if (p)
         return 1;
@@ -43,6 +43,11 @@ main ()
         return 3;
       if (errno != ENOMEM)
         return 4;
+
+      /* Reallocarray should not crash with zero sizes.  */
+      p = reallocarray (p, 0, n);
+      p = reallocarray (p, n, 0);
+      free (p);
     }
 
   return 0;