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

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 13bba02271dc.

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
index ca24620fd0b184f14da5d87702286aa89a94801a..d35deb433aad40d769b58c0229389b8b468acb0c 100644 (file)
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -1163,15 +1163,17 @@ 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;