Use a uintptr_t field at the start of the allocation to store the siz…

…e rather

than a hardcoded 8 bytes. For CHERI, using 8 bytes means that the payload
becomes unaligned.

src/mem1.c

@@ -139,8 +139,9 @@ static void *sqlite3MemMalloc(int nByte){
   sqlite3_int64 *p;
   assert( nByte>0 );
   testcase( ROUND8(nByte)!=nByte );
-  p = SQLITE_MALLOC( nByte+8 );
+  p = SQLITE_MALLOC( nByte+sizeof(uintptr_t) );
   if( p ){
+    p += (sizeof(uintptr_t)/sizeof(int64_t))-1;
     p[0] = nByte;
     p++;
   }else{
@@ -165,7 +166,7 @@ static void sqlite3MemFree(void *pPrior){
 #else
   sqlite3_int64 *p = (sqlite3_int64*)pPrior;
   assert( pPrior!=0 );
-  p--;
+  p -= (sizeof(uintptr_t)/sizeof(int64_t));
   SQLITE_FREE(p);
 #endif
 }
@@ -211,9 +212,10 @@ static void *sqlite3MemRealloc(void *pPrior, int nByte){
   sqlite3_int64 *p = (sqlite3_int64*)pPrior;
   assert( pPrior!=0 && nByte>0 );
   assert( nByte==ROUND8(nByte) ); /* EV: R-46199-30249 */
-  p--;
-  p = SQLITE_REALLOC(p, nByte+8 );
+  p -= (sizeof(uintptr_t)/sizeof(int64_t));
+  p = SQLITE_REALLOC(p, nByte+sizeof(uintptr_t) );
   if( p ){
+    p += (sizeof(uintptr_t)/sizeof(int64_t))-1;
     p[0] = nByte;
     p++;
   }else{