Another attempt to get reuse of excess opcode array space working correctly

on all architectures and platforms.

FossilOrigin-Name: 2f8583748abab1e15029d3a8693ba9a66c978c2b

1 files changed, 11 insertions, 6 deletions

diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index de7f48212..dbbb2a6cc 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -1851,19 +1851,24 @@ void sqlite3VdbeMakeReady(
   /* zCsr will initially point to nFree bytes of unused space at the
   ** end of the opcode array, p->aOp.  The computation of nFree is
   ** conservative - it might be smaller than the true number of free
-  ** bytes, but never larger.  nFree might be negative.  But the allocation
-  ** loop will still function correctly.
+  ** bytes, but never larger.  nFree must be a multiple of 8 - it is
+  ** rounded down if is not.
   */
-  zCsr = ((u8*)p->aOp) + ROUND8(sizeof(Op)*p->nOp);      /* Available space */
-  nFree = pParse->szOpAlloc - ROUND8(sizeof(Op)*p->nOp); /* Size of zCsr */
-  if( nFree>0 ) memset(zCsr, 0, nFree);
+  n = ROUND8(sizeof(Op)*p->nOp);              /* Bytes of opcode space used */
+  zCsr = &((u8*)p->aOp)[n];                   /* Unused opcode space */
+  assert( EIGHT_BYTE_ALIGNMENT(zCsr) );
+  nFree = ROUNDDOWN8(pParse->szOpAlloc - n);  /* Bytes of unused space */
+  assert( nFree>=0 );
+  if( nFree>0 ){
+    memset(zCsr, 0, nFree);
+    assert( EIGHT_BYTE_ALIGNMENT(&zCsr[nFree]) );
+  }
 
   resolveP2Values(p, &nArg);
   p->usesStmtJournal = (u8)(pParse->isMultiWrite && pParse->mayAbort);
   if( pParse->explain && nMem<10 ){
     nMem = 10;
   }
-  assert( EIGHT_BYTE_ALIGNMENT(&zCsr[nFree]) );
   p->expired = 0;
 
   /* Memory for registers, parameters, cursor, etc, is allocated in two