From 26cc27541d92572dbd2a7898bef903aea66ca18f Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 5 Oct 2018 16:01:30 -0400 Subject: [PATCH] Allow btree comparison functions to return INT_MIN. Historically we forbade datatype-specific comparison functions from returning INT_MIN, so that it would be safe to invert the sort order just by negating the comparison result. However, this was never really safe for comparison functions that directly return the result of memcmp(), strcmp(), etc, as POSIX doesn't place any such restriction on those library functions. Buildfarm results show that at least on recent Linux on s390x, memcmp() actually does return INT_MIN sometimes, causing sort failures. The agreed-on answer is to remove this restriction and fix relevant call sites to not make such an assumption; code such as "res = -res" should be replaced by "INVERT_COMPARE_RESULT(res)". The same is needed in a few places that just directly negated the result of memcmp or strcmp. To help find places having this problem, I've also added a compile option to nbtcompare.c that causes some of the commonly used comparators to return INT_MIN/INT_MAX instead of their usual -1/+1. It'd likely be a good idea to have at least one buildfarm member running with "-DSTRESS_SORT_INT_MIN". That's far from a complete test of course, but it should help to prevent fresh introductions of such bugs. This is a longstanding portability hazard, so back-patch to all supported branches. Discussion: https://postgr.es/m/20180928185215.ffoq2xrq5d3pafna@alap3.anarazel.de --- contrib/ltree/ltree_op.c | 11 +++- contrib/pgcrypto/imath.c | 15 ++--- src/backend/access/nbtree/nbtcompare.c | 77 ++++++++++++++++---------- src/backend/access/nbtree/nbtsearch.c | 2 +- src/backend/access/nbtree/nbtsort.c | 2 +- src/backend/access/nbtree/nbtutils.c | 4 +- src/backend/executor/nodeMergeAppend.c | 5 +- src/backend/utils/sort/tuplesort.c | 2 +- src/include/access/nbtree.h | 3 +- src/include/c.h | 8 +++ src/include/utils/sortsupport.h | 5 +- 11 files changed, 82 insertions(+), 52 deletions(-) diff --git a/contrib/ltree/ltree_op.c b/contrib/ltree/ltree_op.c index cb59d21ced4..d1067f81465 100644 --- a/contrib/ltree/ltree_op.c +++ b/contrib/ltree/ltree_op.c @@ -45,17 +45,24 @@ ltree_compare(const ltree *a, const ltree *b) ltree_level *bl = LTREE_FIRST(b); int an = a->numlevel; int bn = b->numlevel; - int res = 0; while (an > 0 && bn > 0) { + int res; + if ((res = memcmp(al->name, bl->name, Min(al->len, bl->len))) == 0) { if (al->len != bl->len) return (al->len - bl->len) * 10 * (an + 1); } else + { + if (res < 0) + res = -1; + else + res = 1; return res * 10 * (an + 1); + } an--; bn--; @@ -146,7 +153,7 @@ inner_isparent(const ltree *c, const ltree *p) { if (cl->len != pl->len) return false; - if (memcmp(cl->name, pl->name, cl->len)) + if (memcmp(cl->name, pl->name, cl->len) != 0) return false; pn--; diff --git a/contrib/pgcrypto/imath.c b/contrib/pgcrypto/imath.c index 61a01e2b710..6449dd34b0b 100644 --- a/contrib/pgcrypto/imath.c +++ b/contrib/pgcrypto/imath.c @@ -1254,11 +1254,9 @@ mp_int_compare(mp_int a, mp_int b) * If they're both zero or positive, the normal comparison applies; if * both negative, the sense is reversed. */ - if (sa == MP_ZPOS) - return cmp; - else - return -cmp; - + if (sa != MP_ZPOS) + INVERT_COMPARE_RESULT(cmp); + return cmp; } else { @@ -1314,10 +1312,9 @@ mp_int_compare_value(mp_int z, int value) { cmp = s_vcmp(z, value); - if (vsign == MP_ZPOS) - return cmp; - else - return -cmp; + if (vsign != MP_ZPOS) + INVERT_COMPARE_RESULT(cmp); + return cmp; } else { diff --git a/src/backend/access/nbtree/nbtcompare.c b/src/backend/access/nbtree/nbtcompare.c index b1f9ae36850..88e07e1bf87 100644 --- a/src/backend/access/nbtree/nbtcompare.c +++ b/src/backend/access/nbtree/nbtcompare.c @@ -22,11 +22,10 @@ * * The result is always an int32 regardless of the input datatype. * - * Although any negative int32 (except INT_MIN) is acceptable for reporting - * "<", and any positive int32 is acceptable for reporting ">", routines + * Although any negative int32 is acceptable for reporting "<", + * and any positive int32 is acceptable for reporting ">", routines * that work on 32-bit or wider datatypes can't just return "a - b". - * That could overflow and give the wrong answer. Also, one must not - * return INT_MIN to report "<", since some callers will negate the result. + * That could overflow and give the wrong answer. * * NOTE: it is critical that the comparison function impose a total order * on all non-NULL values of the data type, and that the datatype's @@ -44,13 +43,31 @@ * during an index access won't be recovered till end of query. This * primarily affects comparison routines for toastable datatypes; * they have to be careful to free any detoasted copy of an input datum. + * + * NOTE: we used to forbid comparison functions from returning INT_MIN, + * but that proves to be too error-prone because some platforms' versions + * of memcmp() etc can return INT_MIN. As a means of stress-testing + * callers, this file can be compiled with STRESS_SORT_INT_MIN defined + * to cause many of these functions to return INT_MIN or INT_MAX instead of + * their customary -1/+1. For production, though, that's not a good idea + * since users or third-party code might expect the traditional results. *------------------------------------------------------------------------- */ #include "postgres.h" +#include + #include "utils/builtins.h" #include "utils/sortsupport.h" +#ifdef STRESS_SORT_INT_MIN +#define A_LESS_THAN_B INT_MIN +#define A_GREATER_THAN_B INT_MAX +#else +#define A_LESS_THAN_B (-1) +#define A_GREATER_THAN_B 1 +#endif + Datum btboolcmp(PG_FUNCTION_ARGS) @@ -95,11 +112,11 @@ btint4cmp(PG_FUNCTION_ARGS) int32 b = PG_GETARG_INT32(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } static int @@ -109,11 +126,11 @@ btint4fastcmp(Datum x, Datum y, SortSupport ssup) int32 b = DatumGetInt32(y); if (a > b) - return 1; + return A_GREATER_THAN_B; else if (a == b) return 0; else - return -1; + return A_LESS_THAN_B; } Datum @@ -132,11 +149,11 @@ btint8cmp(PG_FUNCTION_ARGS) int64 b = PG_GETARG_INT64(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } static int @@ -146,11 +163,11 @@ btint8fastcmp(Datum x, Datum y, SortSupport ssup) int64 b = DatumGetInt64(y); if (a > b) - return 1; + return A_GREATER_THAN_B; else if (a == b) return 0; else - return -1; + return A_LESS_THAN_B; } Datum @@ -169,11 +186,11 @@ btint48cmp(PG_FUNCTION_ARGS) int64 b = PG_GETARG_INT64(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -183,11 +200,11 @@ btint84cmp(PG_FUNCTION_ARGS) int32 b = PG_GETARG_INT32(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -197,11 +214,11 @@ btint24cmp(PG_FUNCTION_ARGS) int32 b = PG_GETARG_INT32(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -211,11 +228,11 @@ btint42cmp(PG_FUNCTION_ARGS) int16 b = PG_GETARG_INT16(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -225,11 +242,11 @@ btint28cmp(PG_FUNCTION_ARGS) int64 b = PG_GETARG_INT64(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -239,11 +256,11 @@ btint82cmp(PG_FUNCTION_ARGS) int16 b = PG_GETARG_INT16(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } Datum @@ -253,11 +270,11 @@ btoidcmp(PG_FUNCTION_ARGS) Oid b = PG_GETARG_OID(1); if (a > b) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else if (a == b) PG_RETURN_INT32(0); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } static int @@ -267,11 +284,11 @@ btoidfastcmp(Datum x, Datum y, SortSupport ssup) Oid b = DatumGetObjectId(y); if (a > b) - return 1; + return A_GREATER_THAN_B; else if (a == b) return 0; else - return -1; + return A_LESS_THAN_B; } Datum @@ -299,9 +316,9 @@ btoidvectorcmp(PG_FUNCTION_ARGS) if (a->values[i] != b->values[i]) { if (a->values[i] > b->values[i]) - PG_RETURN_INT32(1); + PG_RETURN_INT32(A_GREATER_THAN_B); else - PG_RETURN_INT32(-1); + PG_RETURN_INT32(A_LESS_THAN_B); } } PG_RETURN_INT32(0); diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index 203b9691baa..dfdc8945594 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -453,7 +453,7 @@ _bt_compare(Relation rel, scankey->sk_argument)); if (!(scankey->sk_flags & SK_BT_DESC)) - result = -result; + INVERT_COMPARE_RESULT(result); } /* if the keys are unequal, return the difference */ diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c index 1281a120c56..5a74f9b1b84 100644 --- a/src/backend/access/nbtree/nbtsort.c +++ b/src/backend/access/nbtree/nbtsort.c @@ -746,7 +746,7 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2) attrDatum2)); if (entry->sk_flags & SK_BT_DESC) - compare = -compare; + INVERT_COMPARE_RESULT(compare); } if (compare > 0) { diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c index 5ed732e2fe9..05a4d3c374e 100644 --- a/src/backend/access/nbtree/nbtutils.c +++ b/src/backend/access/nbtree/nbtutils.c @@ -509,7 +509,7 @@ _bt_compare_array_elements(const void *a, const void *b, void *arg) cxt->collation, da, db)); if (cxt->reverse) - compare = -compare; + INVERT_COMPARE_RESULT(compare); return compare; } @@ -1638,7 +1638,7 @@ _bt_check_rowcompare(ScanKey skey, IndexTuple tuple, TupleDesc tupdesc, subkey->sk_argument)); if (subkey->sk_flags & SK_BT_DESC) - cmpresult = -cmpresult; + INVERT_COMPARE_RESULT(cmpresult); /* Done comparing if unequal, else advance to next column */ if (cmpresult != 0) diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c index 47ed068c7b7..a32d66ca766 100644 --- a/src/backend/executor/nodeMergeAppend.c +++ b/src/backend/executor/nodeMergeAppend.c @@ -241,7 +241,10 @@ heap_compare_slots(Datum a, Datum b, void *arg) datum2, isNull2, sortKey); if (compare != 0) - return -compare; + { + INVERT_COMPARE_RESULT(compare); + return compare; + } } return 0; } diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c index 9b61a893ca1..2cf713eb63e 100644 --- a/src/backend/utils/sort/tuplesort.c +++ b/src/backend/utils/sort/tuplesort.c @@ -2849,7 +2849,7 @@ inlineApplySortFunction(FmgrInfo *sortFunction, int sk_flags, Oid collation, datum1, datum2)); if (sk_flags & SK_BT_DESC) - compare = -compare; + INVERT_COMPARE_RESULT(compare); } return compare; diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h index 09708c01c81..61f4574948d 100644 --- a/src/include/access/nbtree.h +++ b/src/include/access/nbtree.h @@ -449,8 +449,7 @@ typedef struct xl_btree_newroot * When a new operator class is declared, we require that the user * supply us with an amproc procedure (BTORDER_PROC) for determining * whether, for two keys a and b, a < b, a = b, or a > b. This routine - * must return < 0, 0, > 0, respectively, in these three cases. (It must - * not return INT_MIN, since we may negate the result before using it.) + * must return < 0, 0, > 0, respectively, in these three cases. * * To facilitate accelerated sorting, an operator class may choose to * offer a second procedure (BTSORTSUPPORT_PROC). For full details, see diff --git a/src/include/c.h b/src/include/c.h index 6836b0a0f56..aad18a7c651 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -867,6 +867,14 @@ typedef NameData *Name; * ---------------------------------------------------------------- */ +/* + * Invert the sign of a qsort-style comparison result, ie, exchange negative + * and positive integer values, being careful not to get the wrong answer + * for INT_MIN. The argument should be an integral variable. + */ +#define INVERT_COMPARE_RESULT(var) \ + ((var) = ((var) < 0) ? 1 : -(var)) + /* * Use this, not "char buf[BLCKSZ]", to declare a field or local variable * holding a page buffer, if that page might be accessed as a page and not diff --git a/src/include/utils/sortsupport.h b/src/include/utils/sortsupport.h index 8b6b0de2e8b..2e4dba334d2 100644 --- a/src/include/utils/sortsupport.h +++ b/src/include/utils/sortsupport.h @@ -90,8 +90,7 @@ typedef struct SortSupportData * Comparator function has the same API as the traditional btree * comparison function, ie, return <0, 0, or >0 according as x is less * than, equal to, or greater than y. Note that x and y are guaranteed - * not null, and there is no way to return null either. Do not return - * INT_MIN, as callers are allowed to negate the result before using it. + * not null, and there is no way to return null either. */ int (*comparator) (Datum x, Datum y, SortSupport ssup); @@ -142,7 +141,7 @@ ApplySortComparator(Datum datum1, bool isNull1, { compare = (*ssup->comparator) (datum1, datum2, ssup); if (ssup->ssup_reverse) - compare = -compare; + INVERT_COMPARE_RESULT(compare); } return compare;