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Commit73b96ba

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Fix alignment in BRIN minmax-multi deserialization
The deserialization failed to ensure correct alignment, as it assumed itcan simply point into the serialized value. The serialization howeverignores alignment and copies just the significant bytes in order to makethe result as small as possible. This caused failures on systems thatare sensitive to mialigned addresses, like sparc, or with addresssanitizer enabled.Fixed by copying the serialized data to ensure proper alignment. Whileat it, fix an issue with serialization on big endian machines, using thesame store_att_byval/fetch_att trick as extended statistics.Discussion:https://postgr.es/0c8c3304-d3dd-5e29-d5ac-b50589a23c8c%40enterprisedb.com
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1 file changed

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‎src/backend/access/brin/brin_minmax_multi.c

Lines changed: 74 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -665,7 +665,20 @@ range_serialize(Ranges *range)
665665
{
666666
if (typbyval)/* simple by-value data types */
667667
{
668-
memcpy(ptr,&range->values[i],typlen);
668+
Datumtmp;
669+
670+
/*
671+
* For values passed by value, we need to copy just the
672+
* significant bytes - we can't use memcpy directly, as that
673+
* assumes little endian behavior. store_att_byval does
674+
* almost what we need, but it requires properly aligned
675+
* buffer - the output buffer does not guarantee that. So we
676+
* simply use a local Datum variable (which guarantees proper
677+
* alignment), and then copy the value from it.
678+
*/
679+
store_att_byval(&tmp,range->values[i],typlen);
680+
681+
memcpy(ptr,&tmp,typlen);
669682
ptr+=typlen;
670683
}
671684
elseif (typlen>0)/* fixed-length by-ref types */
@@ -710,9 +723,11 @@ range_deserialize(int maxvalues, SerializedRanges *serialized)
710723
{
711724
inti,
712725
nvalues;
713-
char*ptr;
726+
char*ptr,
727+
*dataptr;
714728
booltypbyval;
715729
inttyplen;
730+
Sizedatalen;
716731

717732
Ranges*range;
718733

@@ -740,34 +755,81 @@ range_deserialize(int maxvalues, SerializedRanges *serialized)
740755
typlen=get_typlen(serialized->typid);
741756

742757
/*
743-
* And now deconstruct the values into Datum array. We don't need to copy
744-
* the values and will instead just point the values to the serialized
745-
* varlena value (assuming it will be kept around).
758+
* And now deconstruct the values into Datum array. We have to copy the
759+
* data because the serialized representation ignores alignment, and we
760+
* don't want to rely it will be kept around anyway.
761+
*/
762+
ptr=serialized->data;
763+
764+
/*
765+
* We don't want to allocate many pieces, so we just allocate everything
766+
* in one chunk. How much space will we need?
767+
*
768+
* XXX We don't need to copy simple by-value data types.
769+
*/
770+
datalen=0;
771+
dataptr=NULL;
772+
for (i=0; (i<nvalues)&& (!typbyval);i++)
773+
{
774+
if (typlen>0)/* fixed-length by-ref types */
775+
datalen+=MAXALIGN(typlen);
776+
elseif (typlen==-1)/* varlena */
777+
{
778+
datalen+=MAXALIGN(VARSIZE_ANY(DatumGetPointer(ptr)));
779+
ptr+=VARSIZE_ANY(DatumGetPointer(ptr));
780+
}
781+
elseif (typlen==-2)/* cstring */
782+
{
783+
datalen+=MAXALIGN(strlen(DatumGetPointer(ptr))+1);
784+
ptr+=strlen(DatumGetPointer(ptr))+1;
785+
}
786+
}
787+
788+
if (datalen>0)
789+
dataptr=palloc(datalen);
790+
791+
/*
792+
* Restore the source pointer (might have been modified when calculating
793+
* the space we need to allocate).
746794
*/
747795
ptr=serialized->data;
748796

749797
for (i=0;i<nvalues;i++)
750798
{
751799
if (typbyval)/* simple by-value data types */
752800
{
753-
memcpy(&range->values[i],ptr,typlen);
801+
Datumv=0;
802+
803+
memcpy(&v,ptr,typlen);
804+
805+
range->values[i]=fetch_att(&v, true,typlen);
754806
ptr+=typlen;
755807
}
756808
elseif (typlen>0)/* fixed-length by-ref types */
757809
{
758-
/* no copy, just set the value to the pointer */
759-
range->values[i]=PointerGetDatum(ptr);
810+
range->values[i]=PointerGetDatum(dataptr);
811+
812+
memcpy(dataptr,ptr,typlen);
813+
dataptr+=MAXALIGN(typlen);
814+
760815
ptr+=typlen;
761816
}
762817
elseif (typlen==-1)/* varlena */
763818
{
764-
range->values[i]=PointerGetDatum(ptr);
765-
ptr+=VARSIZE_ANY(DatumGetPointer(range->values[i]));
819+
range->values[i]=PointerGetDatum(dataptr);
820+
821+
memcpy(dataptr,ptr,VARSIZE_ANY(ptr));
822+
dataptr+=MAXALIGN(VARSIZE_ANY(ptr));
823+
ptr+=VARSIZE_ANY(ptr);
766824
}
767825
elseif (typlen==-2)/* cstring */
768826
{
769-
range->values[i]=PointerGetDatum(ptr);
770-
ptr+=strlen(DatumGetPointer(range->values[i]))+1;
827+
Sizeslen=strlen(ptr)+1;
828+
range->values[i]=PointerGetDatum(dataptr);
829+
830+
memcpy(dataptr,ptr,slen);
831+
dataptr+=MAXALIGN(slen);
832+
ptr+= (slen);
771833
}
772834

773835
/* make sure we haven't overflown the buffer end */
@@ -2823,7 +2885,6 @@ minmax_multi_get_strategy_procinfo(BrinDesc *bdesc, uint16 attno, Oid subtype,
28232885
ObjectIdGetDatum(attr->atttypid),
28242886
ObjectIdGetDatum(subtype),
28252887
Int16GetDatum(strategynum));
2826-
28272888
if (!HeapTupleIsValid(tuple))
28282889
elog(ERROR,"missing operator %d(%u,%u) in opfamily %u",
28292890
strategynum,attr->atttypid,subtype,opfamily);

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