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Commit0cc864b

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Handle unaligned SerializeSnapshot() buffer.
Likewise in RestoreSnapshot(). Do so by copying between the user bufferand a stack buffer of known alignment. Back-patch to 9.6, where thislast applies cleanly. In master, the select_parallel test dies withSIGBUS on "Oracle Solaris 10 1/13 s10s_u11wos_24a SPARC", building32-bit with gcc 4.9.2. In 9.6 and 9.5, the buffers in question happento be sufficiently-aligned, and this change is mere insurance againstfuture 9.6 changes or extension code compromising that.
1 parent3a1a422 commit0cc864b

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1 file changed

+40
-36
lines changed

1 file changed

+40
-36
lines changed

‎src/backend/utils/time/snapmgr.c

Lines changed: 40 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -2012,34 +2012,37 @@ EstimateSnapshotSpace(Snapshot snap)
20122012
void
20132013
SerializeSnapshot(Snapshotsnapshot,char*start_address)
20142014
{
2015-
SerializedSnapshotData*serialized_snapshot;
2015+
SerializedSnapshotDataserialized_snapshot;
20162016

20172017
Assert(snapshot->subxcnt >=0);
20182018

2019-
serialized_snapshot= (SerializedSnapshotData*)start_address;
2020-
20212019
/* Copy all required fields */
2022-
serialized_snapshot->xmin=snapshot->xmin;
2023-
serialized_snapshot->xmax=snapshot->xmax;
2024-
serialized_snapshot->xcnt=snapshot->xcnt;
2025-
serialized_snapshot->subxcnt=snapshot->subxcnt;
2026-
serialized_snapshot->suboverflowed=snapshot->suboverflowed;
2027-
serialized_snapshot->takenDuringRecovery=snapshot->takenDuringRecovery;
2028-
serialized_snapshot->curcid=snapshot->curcid;
2029-
serialized_snapshot->whenTaken=snapshot->whenTaken;
2030-
serialized_snapshot->lsn=snapshot->lsn;
2020+
serialized_snapshot.xmin=snapshot->xmin;
2021+
serialized_snapshot.xmax=snapshot->xmax;
2022+
serialized_snapshot.xcnt=snapshot->xcnt;
2023+
serialized_snapshot.subxcnt=snapshot->subxcnt;
2024+
serialized_snapshot.suboverflowed=snapshot->suboverflowed;
2025+
serialized_snapshot.takenDuringRecovery=snapshot->takenDuringRecovery;
2026+
serialized_snapshot.curcid=snapshot->curcid;
2027+
serialized_snapshot.whenTaken=snapshot->whenTaken;
2028+
serialized_snapshot.lsn=snapshot->lsn;
20312029

20322030
/*
20332031
* Ignore the SubXID array if it has overflowed, unless the snapshot was
20342032
* taken during recovey - in that case, top-level XIDs are in subxip as
20352033
* well, and we mustn't lose them.
20362034
*/
2037-
if (serialized_snapshot->suboverflowed&& !snapshot->takenDuringRecovery)
2038-
serialized_snapshot->subxcnt=0;
2035+
if (serialized_snapshot.suboverflowed&& !snapshot->takenDuringRecovery)
2036+
serialized_snapshot.subxcnt=0;
2037+
2038+
/* Copy struct to possibly-unaligned buffer */
2039+
memcpy(start_address,
2040+
&serialized_snapshot,sizeof(SerializedSnapshotData));
20392041

20402042
/* Copy XID array */
20412043
if (snapshot->xcnt>0)
2042-
memcpy((TransactionId*) (serialized_snapshot+1),
2044+
memcpy((TransactionId*) (start_address+
2045+
sizeof(SerializedSnapshotData)),
20432046
snapshot->xip,snapshot->xcnt*sizeof(TransactionId));
20442047

20452048
/*
@@ -2048,12 +2051,12 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
20482051
* snapshot taken during recovery; all the top-level XIDs are in subxip as
20492052
* well in that case, so we mustn't lose them.
20502053
*/
2051-
if (serialized_snapshot->subxcnt>0)
2054+
if (serialized_snapshot.subxcnt>0)
20522055
{
20532056
Sizesubxipoff=sizeof(SerializedSnapshotData)+
20542057
snapshot->xcnt*sizeof(TransactionId);
20552058

2056-
memcpy((TransactionId*) ((char*)serialized_snapshot+subxipoff),
2059+
memcpy((TransactionId*) (start_address+subxipoff),
20572060
snapshot->subxip,snapshot->subxcnt*sizeof(TransactionId));
20582061
}
20592062
}
@@ -2068,50 +2071,51 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
20682071
Snapshot
20692072
RestoreSnapshot(char*start_address)
20702073
{
2071-
SerializedSnapshotData*serialized_snapshot;
2074+
SerializedSnapshotDataserialized_snapshot;
20722075
Sizesize;
20732076
Snapshotsnapshot;
20742077
TransactionId*serialized_xids;
20752078

2076-
serialized_snapshot= (SerializedSnapshotData*)start_address;
2079+
memcpy(&serialized_snapshot,start_address,
2080+
sizeof(SerializedSnapshotData));
20772081
serialized_xids= (TransactionId*)
20782082
(start_address+sizeof(SerializedSnapshotData));
20792083

20802084
/* We allocate any XID arrays needed in the same palloc block. */
20812085
size=sizeof(SnapshotData)
2082-
+serialized_snapshot->xcnt*sizeof(TransactionId)
2083-
+serialized_snapshot->subxcnt*sizeof(TransactionId);
2086+
+serialized_snapshot.xcnt*sizeof(TransactionId)
2087+
+serialized_snapshot.subxcnt*sizeof(TransactionId);
20842088

20852089
/* Copy all required fields */
20862090
snapshot= (Snapshot)MemoryContextAlloc(TopTransactionContext,size);
20872091
snapshot->satisfies=HeapTupleSatisfiesMVCC;
2088-
snapshot->xmin=serialized_snapshot->xmin;
2089-
snapshot->xmax=serialized_snapshot->xmax;
2092+
snapshot->xmin=serialized_snapshot.xmin;
2093+
snapshot->xmax=serialized_snapshot.xmax;
20902094
snapshot->xip=NULL;
2091-
snapshot->xcnt=serialized_snapshot->xcnt;
2095+
snapshot->xcnt=serialized_snapshot.xcnt;
20922096
snapshot->subxip=NULL;
2093-
snapshot->subxcnt=serialized_snapshot->subxcnt;
2094-
snapshot->suboverflowed=serialized_snapshot->suboverflowed;
2095-
snapshot->takenDuringRecovery=serialized_snapshot->takenDuringRecovery;
2096-
snapshot->curcid=serialized_snapshot->curcid;
2097-
snapshot->whenTaken=serialized_snapshot->whenTaken;
2098-
snapshot->lsn=serialized_snapshot->lsn;
2097+
snapshot->subxcnt=serialized_snapshot.subxcnt;
2098+
snapshot->suboverflowed=serialized_snapshot.suboverflowed;
2099+
snapshot->takenDuringRecovery=serialized_snapshot.takenDuringRecovery;
2100+
snapshot->curcid=serialized_snapshot.curcid;
2101+
snapshot->whenTaken=serialized_snapshot.whenTaken;
2102+
snapshot->lsn=serialized_snapshot.lsn;
20992103

21002104
/* Copy XIDs, if present. */
2101-
if (serialized_snapshot->xcnt>0)
2105+
if (serialized_snapshot.xcnt>0)
21022106
{
21032107
snapshot->xip= (TransactionId*) (snapshot+1);
21042108
memcpy(snapshot->xip,serialized_xids,
2105-
serialized_snapshot->xcnt*sizeof(TransactionId));
2109+
serialized_snapshot.xcnt*sizeof(TransactionId));
21062110
}
21072111

21082112
/* Copy SubXIDs, if present. */
2109-
if (serialized_snapshot->subxcnt>0)
2113+
if (serialized_snapshot.subxcnt>0)
21102114
{
21112115
snapshot->subxip= ((TransactionId*) (snapshot+1))+
2112-
serialized_snapshot->xcnt;
2113-
memcpy(snapshot->subxip,serialized_xids+serialized_snapshot->xcnt,
2114-
serialized_snapshot->subxcnt*sizeof(TransactionId));
2116+
serialized_snapshot.xcnt;
2117+
memcpy(snapshot->subxip,serialized_xids+serialized_snapshot.xcnt,
2118+
serialized_snapshot.subxcnt*sizeof(TransactionId));
21152119
}
21162120

21172121
/* Set the copied flag so that the caller will set refcounts correctly. */

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