diff -r e3123b88d012 memory.c
--- a/memory.c	Tue Aug 16 22:02:45 2022 +0200
+++ b/memory.c	Fri Aug 19 06:25:37 2022 +0900
@@ -29,7 +29,8 @@
 see https://www.gnu.org/licenses/.  */
 
 #include <stdio.h>
-#include <stdlib.h> /* for malloc, realloc, free */
+#include <stdlib.h> /* for malloc, free */
+#include <string.h> /* for memcpy, explicit_bzero */
 
 #include "gmp-impl.h"
 
@@ -98,11 +99,28 @@
   new_size += 2 * GMP_LIMB_BYTES;
 #endif
 
-  ret = realloc (oldptr, new_size);
-  if (ret == 0)
+  if (new_size == 0)
+    {
+      explicit_bzero (oldptr, old_size);
+      free (oldptr);
+      return NULL;
+    }
+  else if (old_size == new_size)
+    return oldptr;
+  else
     {
-      fprintf (stderr, "GNU MP: Cannot reallocate memory (old_size=%lu new_size=%lu)\n", (long) old_size, (long) new_size);
-      abort ();
+      /* We can't simply call realloc, as it may allocate memory from
+	 a different arena.  */
+      ret = malloc (new_size);
+      if (ret == NULL)
+	{
+	  fprintf (stderr, "GNU MP: Cannot reallocate memory (old_size=%lu new_size=%lu)\n", (long) old_size, (long) new_size);
+	  explicit_bzero(oldptr, old_size);
+	  abort();
+	}
+      memcpy (ret, oldptr, MIN(old_size, new_size));
+      explicit_bzero (oldptr, old_size);
+      free (oldptr);
     }
 
 #ifdef DEBUG
@@ -141,5 +159,6 @@
     blk_ptr = p - 1;
   }
 #endif
+  explicit_bzero (blk_ptr, blk_size);
   free (blk_ptr);
 }