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Commit7f31121

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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 parent4461a9b commit7f31121

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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
@@ -2015,34 +2015,37 @@ EstimateSnapshotSpace(Snapshot snap)
20152015
void
20162016
SerializeSnapshot(Snapshotsnapshot,char*start_address)
20172017
{
2018-
SerializedSnapshotData*serialized_snapshot;
2018+
SerializedSnapshotDataserialized_snapshot;
20192019

20202020
Assert(snapshot->subxcnt >=0);
20212021

2022-
serialized_snapshot= (SerializedSnapshotData*)start_address;
2023-
20242022
/* Copy all required fields */
2025-
serialized_snapshot->xmin=snapshot->xmin;
2026-
serialized_snapshot->xmax=snapshot->xmax;
2027-
serialized_snapshot->xcnt=snapshot->xcnt;
2028-
serialized_snapshot->subxcnt=snapshot->subxcnt;
2029-
serialized_snapshot->suboverflowed=snapshot->suboverflowed;
2030-
serialized_snapshot->takenDuringRecovery=snapshot->takenDuringRecovery;
2031-
serialized_snapshot->curcid=snapshot->curcid;
2032-
serialized_snapshot->whenTaken=snapshot->whenTaken;
2033-
serialized_snapshot->lsn=snapshot->lsn;
2023+
serialized_snapshot.xmin=snapshot->xmin;
2024+
serialized_snapshot.xmax=snapshot->xmax;
2025+
serialized_snapshot.xcnt=snapshot->xcnt;
2026+
serialized_snapshot.subxcnt=snapshot->subxcnt;
2027+
serialized_snapshot.suboverflowed=snapshot->suboverflowed;
2028+
serialized_snapshot.takenDuringRecovery=snapshot->takenDuringRecovery;
2029+
serialized_snapshot.curcid=snapshot->curcid;
2030+
serialized_snapshot.whenTaken=snapshot->whenTaken;
2031+
serialized_snapshot.lsn=snapshot->lsn;
20342032

20352033
/*
20362034
* Ignore the SubXID array if it has overflowed, unless the snapshot was
20372035
* taken during recovey - in that case, top-level XIDs are in subxip as
20382036
* well, and we mustn't lose them.
20392037
*/
2040-
if (serialized_snapshot->suboverflowed&& !snapshot->takenDuringRecovery)
2041-
serialized_snapshot->subxcnt=0;
2038+
if (serialized_snapshot.suboverflowed&& !snapshot->takenDuringRecovery)
2039+
serialized_snapshot.subxcnt=0;
2040+
2041+
/* Copy struct to possibly-unaligned buffer */
2042+
memcpy(start_address,
2043+
&serialized_snapshot,sizeof(SerializedSnapshotData));
20422044

20432045
/* Copy XID array */
20442046
if (snapshot->xcnt>0)
2045-
memcpy((TransactionId*) (serialized_snapshot+1),
2047+
memcpy((TransactionId*) (start_address+
2048+
sizeof(SerializedSnapshotData)),
20462049
snapshot->xip,snapshot->xcnt*sizeof(TransactionId));
20472050

20482051
/*
@@ -2051,12 +2054,12 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
20512054
* snapshot taken during recovery; all the top-level XIDs are in subxip as
20522055
* well in that case, so we mustn't lose them.
20532056
*/
2054-
if (serialized_snapshot->subxcnt>0)
2057+
if (serialized_snapshot.subxcnt>0)
20552058
{
20562059
Sizesubxipoff=sizeof(SerializedSnapshotData)+
20572060
snapshot->xcnt*sizeof(TransactionId);
20582061

2059-
memcpy((TransactionId*) ((char*)serialized_snapshot+subxipoff),
2062+
memcpy((TransactionId*) (start_address+subxipoff),
20602063
snapshot->subxip,snapshot->subxcnt*sizeof(TransactionId));
20612064
}
20622065
}
@@ -2071,50 +2074,51 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
20712074
Snapshot
20722075
RestoreSnapshot(char*start_address)
20732076
{
2074-
SerializedSnapshotData*serialized_snapshot;
2077+
SerializedSnapshotDataserialized_snapshot;
20752078
Sizesize;
20762079
Snapshotsnapshot;
20772080
TransactionId*serialized_xids;
20782081

2079-
serialized_snapshot= (SerializedSnapshotData*)start_address;
2082+
memcpy(&serialized_snapshot,start_address,
2083+
sizeof(SerializedSnapshotData));
20802084
serialized_xids= (TransactionId*)
20812085
(start_address+sizeof(SerializedSnapshotData));
20822086

20832087
/* We allocate any XID arrays needed in the same palloc block. */
20842088
size=sizeof(SnapshotData)
2085-
+serialized_snapshot->xcnt*sizeof(TransactionId)
2086-
+serialized_snapshot->subxcnt*sizeof(TransactionId);
2089+
+serialized_snapshot.xcnt*sizeof(TransactionId)
2090+
+serialized_snapshot.subxcnt*sizeof(TransactionId);
20872091

20882092
/* Copy all required fields */
20892093
snapshot= (Snapshot)MemoryContextAlloc(TopTransactionContext,size);
20902094
snapshot->satisfies=HeapTupleSatisfiesMVCC;
2091-
snapshot->xmin=serialized_snapshot->xmin;
2092-
snapshot->xmax=serialized_snapshot->xmax;
2095+
snapshot->xmin=serialized_snapshot.xmin;
2096+
snapshot->xmax=serialized_snapshot.xmax;
20932097
snapshot->xip=NULL;
2094-
snapshot->xcnt=serialized_snapshot->xcnt;
2098+
snapshot->xcnt=serialized_snapshot.xcnt;
20952099
snapshot->subxip=NULL;
2096-
snapshot->subxcnt=serialized_snapshot->subxcnt;
2097-
snapshot->suboverflowed=serialized_snapshot->suboverflowed;
2098-
snapshot->takenDuringRecovery=serialized_snapshot->takenDuringRecovery;
2099-
snapshot->curcid=serialized_snapshot->curcid;
2100-
snapshot->whenTaken=serialized_snapshot->whenTaken;
2101-
snapshot->lsn=serialized_snapshot->lsn;
2100+
snapshot->subxcnt=serialized_snapshot.subxcnt;
2101+
snapshot->suboverflowed=serialized_snapshot.suboverflowed;
2102+
snapshot->takenDuringRecovery=serialized_snapshot.takenDuringRecovery;
2103+
snapshot->curcid=serialized_snapshot.curcid;
2104+
snapshot->whenTaken=serialized_snapshot.whenTaken;
2105+
snapshot->lsn=serialized_snapshot.lsn;
21022106

21032107
/* Copy XIDs, if present. */
2104-
if (serialized_snapshot->xcnt>0)
2108+
if (serialized_snapshot.xcnt>0)
21052109
{
21062110
snapshot->xip= (TransactionId*) (snapshot+1);
21072111
memcpy(snapshot->xip,serialized_xids,
2108-
serialized_snapshot->xcnt*sizeof(TransactionId));
2112+
serialized_snapshot.xcnt*sizeof(TransactionId));
21092113
}
21102114

21112115
/* Copy SubXIDs, if present. */
2112-
if (serialized_snapshot->subxcnt>0)
2116+
if (serialized_snapshot.subxcnt>0)
21132117
{
21142118
snapshot->subxip= ((TransactionId*) (snapshot+1))+
2115-
serialized_snapshot->xcnt;
2116-
memcpy(snapshot->subxip,serialized_xids+serialized_snapshot->xcnt,
2117-
serialized_snapshot->subxcnt*sizeof(TransactionId));
2119+
serialized_snapshot.xcnt;
2120+
memcpy(snapshot->subxip,serialized_xids+serialized_snapshot.xcnt,
2121+
serialized_snapshot.subxcnt*sizeof(TransactionId));
21182122
}
21192123

21202124
/* Set the copied flag so that the caller will set refcounts correctly. */

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