Avoid comparing pointer values after the object that they point to has been

deleted.

FossilOrigin-Name: 2ec7e50cbc0e7a4308d51be3c9416229b187a6a8abdd982c154edc256cd6da1f

manifest

@@ -1,5 +1,5 @@
-C Fix\sminor\scode\sissues\sin\salter.c.
+C Avoid\scomparing\spointer\svalues\safter\sthe\sobject\sthat\sthey\spoint\sto\shas\sbeen\ndeleted.
-D 2018-09-05T08:28:30.162
+D 2018-09-05T14:36:05.795
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 6b650013511fd9d8b094203ac268af9220d292cc7d4e1bc9fbca15aacd8c7995
@@ -434,7 +434,7 @@ F spec.template 86a4a43b99ebb3e75e6b9a735d5fd293a24e90ca
 F sqlite.pc.in 42b7bf0d02e08b9e77734a47798d1a55a9e0716b
 F sqlite3.1 fc7ad8990fc8409983309bb80de8c811a7506786
 F sqlite3.pc.in 48fed132e7cb71ab676105d2a4dc77127d8c1f3a
-F src/alter.c 03195c21c23ee260bc37a94ed971647fc61522a318499dec712c035065327248
+F src/alter.c 900f64f083ca8dde83bb40fde12df29a26dad85d8ad086456bf1b373a2034abf
 F src/analyze.c 3dc6b98cf007b005af89df165c966baaa48e8124f38c87b4d2b276fe7f0b9eb9
 F src/attach.c 4bd5b92633671d3e8ce431153ebb1893b50335818423b5373f3f27969f79769a
 F src/auth.c 32a5bbe3b755169ab6c66311c5225a3cd4f75a46c041f7fb117e0cbb68055114
@@ -444,7 +444,7 @@ F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
 F src/btree.c 3f5e1a03db871e627bf5da21092bf7434ecfc5c5980bbd7d45eba13341340173
 F src/btree.h febb2e817be499570b7a2e32a9bbb4b607a9234f6b84bb9ae84916d4806e96f2
 F src/btreeInt.h 620ab4c7235f43572cf3ac2ac8723cbdf68073be4d29da24897c7b77dda5fd96
-F src/build.c 79c5f75243665d9287e7a58b1a1de898d6f2baa094feeaa0741e40e174fea04d
+F src/build.c 3565efa51996dc501c3008aa73cad5ffeb983d91a73d7499d8e2bf1a886ff381
 F src/callback.c 36caff1e7eb7deb58572d59c41cee8f064a11d00297616995c5050ea0cfc1288
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
 F src/ctime.c b157b01081f92442f8b0218ddb93ddce8ebddad36dbddeecfdd771561dd4f387
@@ -505,7 +505,7 @@ F src/shell.c.in 6e0aad854be738a5d0368940459399be211e9ac43aebe92bb9ed46cfe38d0e1
 F src/sqlite.h.in cdf2a539cd0570322a94bcb97c01c56feb1be0657ec7cfb8273c89d19fff87a9
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 9887b27e69c01e79c2cbe74ef73bf01af5b5703d6a7f0a4371e386d7249cb1c7
-F src/sqliteInt.h 5444fef2e1d7e295e89d570b4abfc9a4170f1599313e0fcef3e5af7695c955c6
+F src/sqliteInt.h 8a75462ee70e76754e88daaa32bf7926ee412a3fea95551dcb1687194ff4da3d
 F src/sqliteLimit.h 1513bfb7b20378aa0041e7022d04acb73525de35b80b252f1b83fedb4de6a76b
 F src/status.c 46e7aec11f79dad50965a5ca5fa9de009f7d6bde08be2156f1538a0a296d4d0e
 F src/table.c b46ad567748f24a326d9de40e5b9659f96ffff34
@@ -1762,7 +1762,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P ef9e088290efa9d0fc36bcdef710cadfef37c8a33f4685dad4ce113807e1cc75
+P 18ba35b86f3b9813179b5f8d74e59e4860bfb800f45aabab8d6c0a6d7c97fe74
-R 3c73ae7419c717f5dc619ede5bd8da02
+R e34731a05ad5e409a1eb5bf8e8e1e91f
 U dan
-Z 6d8c724be6bb52b55bc9a3322b139f49
+Z 9b024d81745c3ab29b2f21a946603a51

manifest.uuid

@@ -1 +1 @@
-18ba35b86f3b9813179b5f8d74e59e4860bfb800f45aabab8d6c0a6d7c97fe74
+2ec7e50cbc0e7a4308d51be3c9416229b187a6a8abdd982c154edc256cd6da1f

src/alter.c

@@ -624,15 +624,45 @@ struct RenameCtx {
   const char *zOld;               /* Old column name */
 };
 
-void renameTokenClear(Parse *pParse, void *pPtr){
+#ifdef SQLITE_DEBUG
-  RenameToken *p;
+/*
-  assert( pPtr || pParse->db->mallocFailed );
+** This function is only for debugging. It performs two tasks:
-  for(p=pParse->pRename; p; p=p->pNext){
+**
-    if( p->p==pPtr ){
+**   1. Checks that pointer pPtr does not already appear in the 
-      p->p = 0;
+**      rename-token list.
+**
+**   2. Dereferences each pointer in the rename-token list.
+**
+** The second is most effective when debugging under valgrind or
+** address-sanitizer or similar. If any of these pointers no longer 
+** point to valid objects, an exception is raised by the memory-checking 
+** tool.
+**
+** The point of this is to prevent comparisons of invalid pointer values.
+** Even though this always seems to work, it is undefined according to the
+** C standard. Example of undefined comparison:
+**
+**     sqlite3_free(x);
+**     if( x==y ) ...
+**
+** Technically, as x no longer points into a valid object or to the byte
+** following a valid object, it may not be used in comparison operations.
+*/
+void renameTokenCheckAll(Parse *pParse, void *pPtr){
+  if( pParse->nErr==0 && pParse->db->mallocFailed==0 ){
+    RenameToken *p;
+    u8 i = 0;
+    for(p=pParse->pRename; p; p=p->pNext){
+      if( p->p ){
+        assert( p->p!=pPtr );
+        i += *(u8*)(p->p);
+      }
     }
   }
 }
+#else
+# define renameTokenCheckAll(x,y)
+#endif
 
 /*
 ** Add a new RenameToken object mapping parse tree element pPtr into
@@ -643,8 +673,7 @@ void renameTokenClear(Parse *pParse, void *pPtr){
 void *sqlite3RenameTokenMap(Parse *pParse, void *pPtr, Token *pToken){
   RenameToken *pNew;
   assert( pPtr || pParse->db->mallocFailed );
-
+  renameTokenCheckAll(pParse, pPtr);
-  renameTokenClear(pParse, pPtr);
   pNew = sqlite3DbMallocZero(pParse->db, sizeof(RenameToken));
   if( pNew ){
     pNew->p = pPtr;
@@ -663,7 +692,7 @@ void *sqlite3RenameTokenMap(Parse *pParse, void *pPtr, Token *pToken){
 */
 void sqlite3RenameTokenRemap(Parse *pParse, void *pTo, void *pFrom){
   RenameToken *p;
-  if( pTo ) renameTokenClear(pParse, pTo);
+  renameTokenCheckAll(pParse, pTo);
   for(p=pParse->pRename; p; p=p->pNext){
     if( p->p==pFrom ){
       p->p = pTo;
@@ -672,6 +701,26 @@ void sqlite3RenameTokenRemap(Parse *pParse, void *pTo, void *pFrom){
   }
 }
 
+/*
+** Walker callback used by sqlite3RenameExprUnmap().
+*/
+static int renameUnmapExprCb(Walker *pWalker, Expr *pExpr){
+  Parse *pParse = pWalker->pParse;
+  sqlite3RenameTokenRemap(pParse, 0, (void*)pExpr);
+  return WRC_Continue;
+}
+
+/*
+** Remove all nodes that are part of expression pExpr from the rename list.
+*/
+void sqlite3RenameExprUnmap(Parse *pParse, Expr *pExpr){
+  Walker sWalker;
+  memset(&sWalker, 0, sizeof(Walker));
+  sWalker.pParse = pParse;
+  sWalker.xExprCallback = renameUnmapExprCb;
+  sqlite3WalkExpr(&sWalker, pExpr);
+}
+
 /*
 ** Free the list of RenameToken objects given in the second argument
 */

src/build.c

@@ -1282,6 +1282,9 @@ void sqlite3AddDefaultValue(
       sqlite3DbFree(db, x.u.zToken);
     }
   }
+  if( IN_RENAME_OBJECT ){
+    sqlite3RenameExprUnmap(pParse, pExpr);
+  }
   sqlite3ExprDelete(db, pExpr);
 }
 

src/sqliteInt.h

@@ -4241,6 +4241,7 @@ void sqlite3AlterFinishAddColumn(Parse *, Token *);
 void sqlite3AlterBeginAddColumn(Parse *, SrcList *);
 void *sqlite3RenameTokenMap(Parse*, void*, Token*);
 void sqlite3RenameTokenRemap(Parse*, void *pTo, void *pFrom);
+void sqlite3RenameExprUnmap(Parse*, Expr*);
 CollSeq *sqlite3GetCollSeq(Parse*, u8, CollSeq *, const char*);
 char sqlite3AffinityType(const char*, Column*);
 void sqlite3Analyze(Parse*, Token*, Token*);