Avoid memcpy() with a NULL source pointer and count == 0

alvherre · alvherre · commit 49aaabdf8d0b · 2020-12-01T11:46:56.000-03:00
When memcpy() is called on a pointer, the compiler is entitled to assume that the pointer is not null, which can lead to optimizing nearby code in potentially undesirable ways. We still want such optimizations (gcc's -fdelete-null-pointer-checks) in cases where they're valid. Related: commit 13bba02. Backpatch to pg11, where this particular instance appeared. Reported-by: Ranier Vilela <ranier.vf@gmail.com> Reported-by: Zhihong Yu <zyu@yugabyte.com> Discussion: https://postgr.es/m/CAEudQApUndmQkr5fLrCKXQ7+ib44i7S+Kk93pyVThS85PnG3bQ@mail.gmail.com Discussion: https://postgr.es/m/CALNJ-vSdhwSM5f4tnNn1cdLHvXMVe_S+V3nR5GwNrmCPNB2VtQ@mail.gmail.com
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
@@ -950,15 +950,17 @@ DefineIndex(Oid relationId,
 
 	if (partitioned)
 	{
+		PartitionDesc partdesc;
+
 		/*
 		 * Unless caller specified to skip this step (via ONLY), process each
 		 * partition to make sure they all contain a corresponding index.
 		 *
 		 * If we're called internally (no stmt->relation), recurse always.
 		 */
-		if (!stmt->relation || stmt->relation->inh)
+		partdesc = RelationGetPartitionDesc(rel);
+		if ((!stmt->relation || stmt->relation->inh) && partdesc->nparts > 0)
 		{
-			PartitionDesc partdesc = RelationGetPartitionDesc(rel);
 			int			nparts = partdesc->nparts;
 			Oid		   *part_oids = palloc(sizeof(Oid) * nparts);
 			bool		invalidate_parent = false;

Original file line number	Diff line number	Diff line change
`@@ -950,15 +950,17 @@ DefineIndex(Oid relationId,`
`950`	`950`
`951`	`951`	`if (partitioned)`
`952`	`952`	`{`
	`953`	`+ PartitionDesc partdesc;`
	`954`	`+`
`953`	`955`	`/*`
`954`	`956`	`* Unless caller specified to skip this step (via ONLY), process each`
`955`	`957`	`* partition to make sure they all contain a corresponding index.`
`956`	`958`	`*`
`957`	`959`	`* If we're called internally (no stmt->relation), recurse always.`
`958`	`960`	`*/`
`959`		`- if (!stmt->relation \|\| stmt->relation->inh)`
	`961`	`+ partdesc = RelationGetPartitionDesc(rel);`
	`962`	`+ if ((!stmt->relation \|\| stmt->relation->inh) && partdesc->nparts > 0)`
`960`	`963`	`{`
`961`		`- PartitionDesc partdesc = RelationGetPartitionDesc(rel);`
`962`	`964`	`int nparts = partdesc->nparts;`
`963`	`965`	`Oid part_oids = palloc(sizeof(Oid) nparts);`
`964`	`966`	`bool invalidate_parent = false;`