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

tglsfdc · tglsfdc · commit d3f4e8a8a78b · 2017-11-25T14:42:10.000-05:00
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 ad520ec). 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
@@ -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++;

Original file line number	Diff line number	Diff line change
`@@ -340,7 +340,8 @@ hstoreUniquePairs(Pairs a, int32 l, int32 buflen)`
`340`	`340`	`{`
`341`	`341`	`*buflen += res->keylen + ((res->isnull) ? 0 : res->vallen);`
`342`	`342`	`res++;`
`343`		`- memcpy(res, ptr, sizeof(Pairs));`
	`343`	`+ if (res != ptr)`
	`344`	`+ memcpy(res, ptr, sizeof(Pairs));`
`344`	`345`	`}`
`345`	`346`
`346`	`347`	`ptr++;`