MDEV-17799 Add ASAN-poisoned redzones for MEM_ROOT and mem_heap_t

This patch is for MEM_ROOT only.
In debug mode add 8 byte of poisoned memory before every allocated chunk.
On the right of every chunk there will be either 1-7 trailing poisoned bytes, or
next chunk's redzone, or poisoned non allocated memory or redzone of a
malloc()ed buffer.

include/my_valgrind.h

@@ -13,6 +13,9 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
 
+#ifndef _my_valgrind_h
+#define _my_valgrind_h
+
 /* clang -> gcc */
 #ifndef __has_feature
 # define __has_feature(x) 0
@@ -49,9 +52,13 @@
 #endif /* HAVE_VALGRIND */
 
 #ifndef DBUG_OFF
+static const size_t REDZONE_SIZE= 8;
 #define TRASH_FILL(A,B,C) do { const size_t trash_tmp= (B); MEM_UNDEFINED(A, trash_tmp); memset(A, C, trash_tmp); } while (0)
 #else
+static const size_t REDZONE_SIZE= 0;
 #define TRASH_FILL(A,B,C) do { MEM_UNDEFINED((A), (B)); } while (0)
 #endif
 #define TRASH_ALLOC(A,B) do { TRASH_FILL(A,B,0xA5); MEM_UNDEFINED(A,B); } while(0)
 #define TRASH_FREE(A,B) do { TRASH_FILL(A,B,0x8F); MEM_NOACCESS(A,B); } while(0)
+
+#endif /* _my_valgrind_h */

mysys/my_alloc.c

@@ -197,7 +197,7 @@ void *alloc_root(MEM_ROOT *mem_root, size_t length)
                     DBUG_SET("-d,simulate_out_of_memory");
                     DBUG_RETURN((void*) 0); /* purecov: inspected */
                   });
-  length= ALIGN_SIZE(length);
+  length= ALIGN_SIZE(length) + REDZONE_SIZE;
   if ((*(prev= &mem_root->free)) != NULL)
   {
     if ((*prev)->left < length &&
@@ -242,6 +242,7 @@ void *alloc_root(MEM_ROOT *mem_root, size_t length)
     mem_root->used= next;
     mem_root->first_block_usage= 0;
   }
+  point+= REDZONE_SIZE;
   TRASH_ALLOC(point, original_length);
   DBUG_PRINT("exit",("ptr: 0x%lx", (ulong) point));
   DBUG_RETURN((void*) point);