Avoid formally-undefined use of memcpy() in hstoreUniquePairs().

hstoreUniquePairs() often called memcpy with equal source and destination
pointers.  Although this is almost surely harmless in practice, it's
undefined according to the letter of the C standard.  Some versions of
valgrind will complain about it, and some versions of libc as well
(cf. commit ad520ec4a).  Tweak the code to avoid doing that.

Noted by Tomas Vondra.  Back-patch to all supported versions because
of the hazard of libc assertions.

Discussion: https://postgr.es/m/bf84d940-90d4-de91-19dd-612e011007f4@fuzzy.cz

diff --git a/contrib/hstore/hstore_io.c b/contrib/hstore/hstore_io.c
index e03005c9232b1244738c21e17f05224472820919..8b44b290e4d82ad3737abdd3e458dca475f1cac0 100644 (file)
--- a/contrib/hstore/hstore_io.c
+++ b/contrib/hstore/hstore_io.c
@@ -340,7 +340,8 @@ hstoreUniquePairs(Pairs *a, int32 l, int32 *buflen)
        {
            *buflen += res->keylen + ((res->isnull) ? 0 : res->vallen);
            res++;
-           memcpy(res, ptr, sizeof(Pairs));
+           if (res != ptr)
+               memcpy(res, ptr, sizeof(Pairs));
        }
 
        ptr++;