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Avoid using potentially-under-aligned page buffers. 

There's a project policy against using plain "char buf[BLCKSZ]" local
or static variables as page buffers; preferred style is to palloc or
malloc each buffer to ensure it is MAXALIGN'd.  However, that policy's
been ignored in an increasing number of places.  We've apparently got
away with it so far, probably because (a) relatively few people use
platforms on which misalignment causes core dumps and/or (b) the
variables chance to be sufficiently aligned anyway.  But this is not
something to rely on.  Moreover, even if we don't get a core dump,
we might be paying a lot of cycles for misaligned accesses.

To fix, invent new union types PGAlignedBlock and PGAlignedXLogBlock
that the compiler must allocate with sufficient alignment, and use
those in place of plain char arrays.

I used these types even for variables where there's no risk of a
misaligned access, since ensuring proper alignment should make
kernel data transfers faster.  I also changed some places where
we had been palloc'ing short-lived buffers, for coding style
uniformity and to save palloc/pfree overhead.

Since this seems to be a live portability hazard (despite the lack
of field reports), back-patch to all supported versions.

Patch by me; thanks to Michael Paquier for review.

Discussion: https://postgr.es/m/1535618100.1286.3.camel@credativ.de
This commit is contained in:
Tom Lane 2018-09-01 15:27:13 -04:00
parent e3eca937c7
commit 03ffe5553c
17 changed files with 90 additions and 101 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
contrib/pg_prewarm/pg_prewarm.c
View File

@ -37,7 +37,7 @@ typedef enum
PREWARM_BUFFER
} PrewarmType;
static char blockbuffer[BLCKSZ];
static PGAlignedBlock blockbuffer;
/*
* pg_prewarm(regclass, mode text, fork text,
@ -179,7 +179,7 @@ pg_prewarm(PG_FUNCTION_ARGS)
for (block = first_block; block <= last_block; ++block)
{
CHECK_FOR_INTERRUPTS();
smgrread(rel->rd_smgr, forkNumber, block, blockbuffer);
smgrread(rel->rd_smgr, forkNumber, block, blockbuffer.data);
++blocks_done;
}
}

6
src/backend/access/gin/ginentrypage.c
View File

@ -615,7 +615,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
Page lpage = PageGetTempPageCopy(BufferGetPage(origbuf));
Page rpage = PageGetTempPageCopy(BufferGetPage(origbuf));
Size pageSize = PageGetPageSize(lpage);
char tupstore[2 * BLCKSZ];
PGAlignedBlock tupstore[2]; /* could need 2 pages' worth of tuples */
entryPreparePage(btree, lpage, off, insertData, updateblkno);
@ -624,7 +624,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
* one after another in a temporary workspace.
*/
maxoff = PageGetMaxOffsetNumber(lpage);
ptr = tupstore;
ptr = tupstore[0].data;
for (i = FirstOffsetNumber; i <= maxoff; i++)
{
if (i == off)
@ -657,7 +657,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
GinInitPage(rpage, GinPageGetOpaque(lpage)->flags, pageSize);
GinInitPage(lpage, GinPageGetOpaque(rpage)->flags, pageSize);
ptr = tupstore;
ptr = tupstore[0].data;
maxoff++;
lsize = 0;

11
src/backend/access/gin/ginfast.c
View File

@ -55,18 +55,15 @@ writeListPage(Relation index, Buffer buffer,
size = 0;
OffsetNumber l,
off;
char *workspace;
PGAlignedBlock workspace;
char *ptr;
/* workspace could be a local array; we use palloc for alignment */
workspace = palloc(BLCKSZ);
START_CRIT_SECTION();
GinInitBuffer(buffer, GIN_LIST);
off = FirstOffsetNumber;
ptr = workspace;
ptr = workspace.data;
for (i = 0; i < ntuples; i++)
{
@ -118,7 +115,7 @@ writeListPage(Relation index, Buffer buffer,
XLogRegisterData((char *) &data, sizeof(ginxlogInsertListPage));
XLogRegisterBuffer(0, buffer, REGBUF_WILL_INIT);
XLogRegisterBufData(0, workspace, size);
XLogRegisterBufData(0, workspace.data, size);
recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_INSERT_LISTPAGE);
PageSetLSN(page, recptr);
@ -131,8 +128,6 @@ writeListPage(Relation index, Buffer buffer,
END_CRIT_SECTION();
pfree(workspace);
return freesize;
}

6
src/backend/access/hash/hashpage.c
View File

@ -710,7 +710,7 @@ static bool
_hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
{
BlockNumber lastblock;
char zerobuf[BLCKSZ];
PGAlignedBlock zerobuf;
lastblock = firstblock + nblocks - 1;
@ -721,10 +721,10 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
if (lastblock < firstblock || lastblock == InvalidBlockNumber)
return false;
MemSet(zerobuf, 0, sizeof(zerobuf));
MemSet(zerobuf.data, 0, sizeof(zerobuf));
RelationOpenSmgr(rel);
smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf, false);
smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf.data, false);
return true;
}

16
src/backend/access/heap/heapam.c
View File

@ -2414,7 +2414,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
HeapTuple *heaptuples;
int i;
int ndone;
char *scratch = NULL;
PGAlignedBlock scratch;
Page page;
bool needwal;
Size saveFreeSpace;
@ -2431,14 +2431,6 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
heaptuples[i] = heap_prepare_insert(relation, tuples[i],
xid, cid, options);
/*
* Allocate some memory to use for constructing the WAL record. Using
* palloc() within a critical section is not safe, so we allocate this
* beforehand.
*/
if (needwal)
scratch = palloc(BLCKSZ);
/*
* We're about to do the actual inserts -- but check for conflict first,
* to minimize the possibility of having to roll back work we've just
@ -2531,7 +2523,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
uint8 info = XLOG_HEAP2_MULTI_INSERT;
char *tupledata;
int totaldatalen;
char *scratchptr = scratch;
char *scratchptr = scratch.data;
bool init;
int bufflags = 0;
@ -2590,7 +2582,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
scratchptr += datalen;
}
totaldatalen = scratchptr - tupledata;
Assert((scratchptr - scratch) < BLCKSZ);
Assert((scratchptr - scratch.data) < BLCKSZ);
if (need_tuple_data)
xlrec->flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
@ -2617,7 +2609,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
bufflags |= REGBUF_KEEP_DATA;
XLogBeginInsert();
XLogRegisterData((char *) xlrec, tupledata - scratch);
XLogRegisterData((char *) xlrec, tupledata - scratch.data);
XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
XLogRegisterBufData(0, tupledata, totaldatalen);

11
src/backend/access/heap/visibilitymap.c
View File

@ -611,10 +611,9 @@ static void
vm_extend(Relation rel, BlockNumber vm_nblocks)
{
BlockNumber vm_nblocks_now;
Page pg;
PGAlignedBlock pg;
pg = (Page) palloc(BLCKSZ);
PageInit(pg, BLCKSZ, 0);
PageInit((Page) pg.data, BLCKSZ, 0);
/*
* We use the relation extension lock to lock out other backends trying to
@ -645,10 +644,10 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
/* Now extend the file */
while (vm_nblocks_now < vm_nblocks)
{
PageSetChecksumInplace(pg, vm_nblocks_now);
PageSetChecksumInplace((Page) pg.data, vm_nblocks_now);
smgrextend(rel->rd_smgr, VISIBILITYMAP_FORKNUM, vm_nblocks_now,
(char *) pg, false);
pg.data, false);
vm_nblocks_now++;
}
@ -665,6 +664,4 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
rel->rd_smgr->smgr_vm_nblocks = vm_nblocks_now;
UnlockRelationForExtension(rel, ExclusiveLock);
pfree(pg);
}

19
src/backend/access/transam/xlog.c
View File

@ -2976,8 +2976,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
{
char path[MAXPGPATH];
char tmppath[MAXPGPATH];
char zbuffer_raw[XLOG_BLCKSZ + MAXIMUM_ALIGNOF];
char *zbuffer;
PGAlignedXLogBlock zbuffer;
XLogSegNo installed_segno;
XLogSegNo max_segno;
int fd;
@ -3031,16 +3030,12 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
* fsync below) that all the indirect blocks are down on disk. Therefore,
* fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
* log file.
*
* Note: ensure the buffer is reasonably well-aligned; this may save a few
* cycles transferring data to the kernel.
*/
zbuffer = (char *) MAXALIGN(zbuffer_raw);
memset(zbuffer, 0, XLOG_BLCKSZ);
memset(zbuffer.data, 0, XLOG_BLCKSZ);
for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
{
errno = 0;
if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
if ((int) write(fd, zbuffer.data, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
{
int save_errno = errno;
@ -3145,7 +3140,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
{
char path[MAXPGPATH];
char tmppath[MAXPGPATH];
char buffer[XLOG_BLCKSZ];
PGAlignedXLogBlock buffer;
int srcfd;
int fd;
int nbytes;
@ -3189,14 +3184,14 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
* zeros.
*/
if (nread < sizeof(buffer))
memset(buffer, 0, sizeof(buffer));
memset(buffer.data, 0, sizeof(buffer));
if (nread > 0)
{
if (nread > sizeof(buffer))
nread = sizeof(buffer);
errno = 0;
if (read(srcfd, buffer, nread) != nread)
if (read(srcfd, buffer.data, nread) != nread)
{
if (errno != 0)
ereport(ERROR,
@ -3210,7 +3205,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
}
}
errno = 0;
if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
if ((int) write(fd, buffer.data, sizeof(buffer)) != (int) sizeof(buffer))
{
int save_errno = errno;

14
src/backend/access/transam/xloginsert.c
View File

@ -774,12 +774,12 @@ XLogCompressBackupBlock(char *page, uint16 hole_offset, uint16 hole_length,
int32 len;
int32 extra_bytes = 0;
char *source;
char tmp[BLCKSZ];
PGAlignedBlock tmp;
if (hole_length != 0)
{
/* must skip the hole */
source = tmp;
source = tmp.data;
memcpy(source, page, hole_offset);
memcpy(source + hole_offset,
page + (hole_offset + hole_length),
@ -882,7 +882,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
if (lsn <= RedoRecPtr)
{
int flags;
char copied_buffer[BLCKSZ];
PGAlignedBlock copied_buffer;
char *origdata = (char *) BufferGetBlock(buffer);
RelFileNode rnode;
ForkNumber forkno;
@ -900,11 +900,11 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
uint16 lower = ((PageHeader) page)->pd_lower;
uint16 upper = ((PageHeader) page)->pd_upper;
memcpy(copied_buffer, origdata, lower);
memcpy(copied_buffer + upper, origdata + upper, BLCKSZ - upper);
memcpy(copied_buffer.data, origdata, lower);
memcpy(copied_buffer.data + upper, origdata + upper, BLCKSZ - upper);
}
else
memcpy(copied_buffer, origdata, BLCKSZ);
memcpy(copied_buffer.data, origdata, BLCKSZ);
XLogBeginInsert();
@ -913,7 +913,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
flags |= REGBUF_STANDARD;
BufferGetTag(buffer, &rnode, &forkno, &blkno);
XLogRegisterBlock(0, &rnode, forkno, blkno, copied_buffer, flags);
XLogRegisterBlock(0, &rnode, forkno, blkno, copied_buffer.data, flags);
recptr = XLogInsert(RM_XLOG_ID, XLOG_FPI_FOR_HINT);
}

6
src/backend/access/transam/xlogreader.c
View File

@ -1375,7 +1375,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
{
DecodedBkpBlock *bkpb;
char *ptr;
char tmp[BLCKSZ];
PGAlignedBlock tmp;
if (!record->blocks[block_id].in_use)
return false;
@ -1388,7 +1388,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
if (bkpb->bimg_info & BKPIMAGE_IS_COMPRESSED)
{
/* If a backup block image is compressed, decompress it */
if (pglz_decompress(ptr, bkpb->bimg_len, tmp,
if (pglz_decompress(ptr, bkpb->bimg_len, tmp.data,
BLCKSZ - bkpb->hole_length) < 0)
{
report_invalid_record(record, "invalid compressed image at %X/%X, block %d",
@ -1397,7 +1397,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
block_id);
return false;
}
ptr = tmp;
ptr = tmp.data;
}
/* generate page, taking into account hole if necessary */

17
src/backend/commands/tablecmds.c
View File

@ -9971,21 +9971,14 @@ static void
copy_relation_data(SMgrRelation src, SMgrRelation dst,
ForkNumber forkNum, char relpersistence)
{
char *buf;
PGAlignedBlock buf;
Page page;
bool use_wal;
bool copying_initfork;
BlockNumber nblocks;
BlockNumber blkno;
/*
* palloc the buffer so that it's MAXALIGN'd. If it were just a local
* char[] array, the compiler might align it on any byte boundary, which
* can seriously hurt transfer speed to and from the kernel; not to
* mention possibly making log_newpage's accesses to the page header fail.
*/
buf = (char *) palloc(BLCKSZ);
page = (Page) buf;
page = (Page) buf.data;
/*
* The init fork for an unlogged relation in many respects has to be
@ -10009,7 +10002,7 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
/* If we got a cancel signal during the copy of the data, quit */
CHECK_FOR_INTERRUPTS();
smgrread(src, forkNum, blkno, buf);
smgrread(src, forkNum, blkno, buf.data);
if (!PageIsVerified(page, blkno))
ereport(ERROR,
@ -10035,11 +10028,9 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
* rel, because there's no need for smgr to schedule an fsync for this
* write; we'll do it ourselves below.
*/
smgrextend(dst, forkNum, blkno, buf, true);
smgrextend(dst, forkNum, blkno, buf.data, true);
}
pfree(buf);
/*
* If the rel is WAL-logged, must fsync before commit. We use heap_sync
* to ensure that the toast table gets fsync'd too. (For a temp or

6
src/backend/replication/walsender.c
View File

@ -495,16 +495,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
bytesleft = histfilelen;
while (bytesleft > 0)
{
char rbuf[BLCKSZ];
PGAlignedBlock rbuf;
int nread;
nread = read(fd, rbuf, sizeof(rbuf));
nread = read(fd, rbuf.data, sizeof(rbuf));
if (nread <= 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read file \"%s\": %m",
path)));
pq_sendbytes(&buf, rbuf, nread);
pq_sendbytes(&buf, rbuf.data, nread);
bytesleft -= nread;
}
CloseTransientFile(fd);

10
src/backend/storage/file/buffile.c
View File

@ -86,7 +86,7 @@ struct BufFile
off_t curOffset; /* offset part of current pos */
int pos; /* next read/write position in buffer */
int nbytes; /* total # of valid bytes in buffer */
char buffer[BLCKSZ];
PGAlignedBlock buffer;
};
static BufFile *makeBufFile(File firstfile);
@ -254,7 +254,7 @@ BufFileLoadBuffer(BufFile *file)
/*
* Read whatever we can get, up to a full bufferload.
*/
file->nbytes = FileRead(thisfile, file->buffer, sizeof(file->buffer));
file->nbytes = FileRead(thisfile, file->buffer.data, sizeof(file->buffer));
if (file->nbytes < 0)
file->nbytes = 0;
file->offsets[file->curFile] += file->nbytes;
@ -317,7 +317,7 @@ BufFileDumpBuffer(BufFile *file)
return; /* seek failed, give up */
file->offsets[file->curFile] = file->curOffset;
}
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);
bytestowrite = FileWrite(thisfile, file->buffer.data + wpos, bytestowrite);
if (bytestowrite <= 0)
return; /* failed to write */
file->offsets[file->curFile] += bytestowrite;
@ -385,7 +385,7 @@ BufFileRead(BufFile *file, void *ptr, size_t size)
nthistime = size;
Assert(nthistime > 0);
memcpy(ptr, file->buffer + file->pos, nthistime);
memcpy(ptr, file->buffer.data + file->pos, nthistime);
file->pos += nthistime;
ptr = (void *) ((char *) ptr + nthistime);
@ -432,7 +432,7 @@ BufFileWrite(BufFile *file, void *ptr, size_t size)
nthistime = size;
Assert(nthistime > 0);
memcpy(file->buffer + file->pos, ptr, nthistime);
memcpy(file->buffer.data + file->pos, ptr, nthistime);
file->dirty = true;
file->pos += nthistime;

11
src/backend/storage/freespace/freespace.c
View File

@ -587,10 +587,9 @@ static void
fsm_extend(Relation rel, BlockNumber fsm_nblocks)
{
BlockNumber fsm_nblocks_now;
Page pg;
PGAlignedBlock pg;
pg = (Page) palloc(BLCKSZ);
PageInit(pg, BLCKSZ, 0);
PageInit((Page) pg.data, BLCKSZ, 0);
/*
* We use the relation extension lock to lock out other backends trying to
@ -620,10 +619,10 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
while (fsm_nblocks_now < fsm_nblocks)
{
PageSetChecksumInplace(pg, fsm_nblocks_now);
PageSetChecksumInplace((Page) pg.data, fsm_nblocks_now);
smgrextend(rel->rd_smgr, FSM_FORKNUM, fsm_nblocks_now,
(char *) pg, false);
pg.data, false);
fsm_nblocks_now++;
}
@ -631,8 +630,6 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
rel->rd_smgr->smgr_fsm_nblocks = fsm_nblocks_now;
UnlockRelationForExtension(rel, ExclusiveLock);
pfree(pg);
}
/*

8
src/bin/pg_basebackup/receivelog.c
View File

@ -108,7 +108,7 @@ open_walfile(XLogRecPtr startpoint, uint32 timeline, char *basedir,
int f;
char fn[MAXPGPATH];
struct stat statbuf;
char *zerobuf;
PGAlignedXLogBlock zerobuf;
int bytes;
XLogSegNo segno;
@ -154,11 +154,11 @@ open_walfile(XLogRecPtr startpoint, uint32 timeline, char *basedir,
}
/* New, empty, file. So pad it to 16Mb with zeroes */
zerobuf = pg_malloc0(XLOG_BLCKSZ);
memset(zerobuf.data, 0, XLOG_BLCKSZ);
for (bytes = 0; bytes < XLogSegSize; bytes += XLOG_BLCKSZ)
{
errno = 0;
if (write(f, zerobuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
if (write(f, zerobuf.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
{
/* if write didn't set errno, assume problem is no disk space */
if (errno == 0)
@ -166,13 +166,11 @@ open_walfile(XLogRecPtr startpoint, uint32 timeline, char *basedir,
fprintf(stderr,
_("%s: could not pad transaction log file \"%s\": %s\n"),
progname, fn, strerror(errno));
free(zerobuf);
close(f);
unlink(fn);
return false;
}
}
free(zerobuf);
if (lseek(f, SEEK_SET, 0) != 0)
{

14
src/bin/pg_resetxlog/pg_resetxlog.c
View File

@ -1133,7 +1133,7 @@ KillExistingArchiveStatus(void)
static void
WriteEmptyXLOG(void)
{
char *buffer;
PGAlignedXLogBlock buffer;
XLogPageHeader page;
XLogLongPageHeader longpage;
XLogRecord *record;
@ -1143,12 +1143,10 @@ WriteEmptyXLOG(void)
int nbytes;
char *recptr;
/* Use malloc() to ensure buffer is MAXALIGNED */
buffer = (char *) pg_malloc(XLOG_BLCKSZ);
page = (XLogPageHeader) buffer;
memset(buffer, 0, XLOG_BLCKSZ);
memset(buffer.data, 0, XLOG_BLCKSZ);
/* Set up the XLOG page header */
page = (XLogPageHeader) buffer.data;
page->xlp_magic = XLOG_PAGE_MAGIC;
page->xlp_info = XLP_LONG_HEADER;
page->xlp_tli = ControlFile.checkPointCopy.ThisTimeLineID;
@ -1194,7 +1192,7 @@ WriteEmptyXLOG(void)
}
errno = 0;
if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
if (write(fd, buffer.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
{
/* if write didn't set errno, assume problem is no disk space */
if (errno == 0)
@ -1205,11 +1203,11 @@ WriteEmptyXLOG(void)
}
/* Fill the rest of the file with zeroes */
memset(buffer, 0, XLOG_BLCKSZ);
memset(buffer.data, 0, XLOG_BLCKSZ);
for (nbytes = XLOG_BLCKSZ; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
{
errno = 0;
if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
if (write(fd, buffer.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
{
if (errno == 0)
errno = ENOSPC;

6
src/bin/pg_rewind/copy_fetch.c
View File

@ -160,7 +160,7 @@ recurse_dir(const char *datadir, const char *parentpath,
static void
rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
{
char buf[BLCKSZ];
PGAlignedBlock buf;
char srcpath[MAXPGPATH];
int srcfd;
@ -186,7 +186,7 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
else
len = end - begin;
readlen = read(srcfd, buf, len);
readlen = read(srcfd, buf.data, len);
if (readlen < 0)
pg_fatal("could not read file \"%s\": %s\n",
@ -194,7 +194,7 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
else if (readlen == 0)
pg_fatal("unexpected EOF while reading file \"%s\"\n", srcpath);
write_target_range(buf, begin, readlen);
write_target_range(buf.data, begin, readlen);
begin += readlen;
}

26
src/include/c.h
View File

@ -960,6 +960,32 @@ typedef NameData *Name;
* ----------------------------------------------------------------
*/
/*
* 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
* just a string of bytes. Otherwise the variable might be under-aligned,
* causing problems on alignment-picky hardware. (In some places, we use
* this to declare buffers even though we only pass them to read() and
* write(), because copying to/from aligned buffers is usually faster than
* using unaligned buffers.) We include both "double" and "int64" in the
* union to ensure that the compiler knows the value must be MAXALIGN'ed
* (cf. configure's computation of MAXIMUM_ALIGNOF).
*/
typedef union PGAlignedBlock
{
char data[BLCKSZ];
double force_align_d;
int64 force_align_i64;
} PGAlignedBlock;
/* Same, but for an XLOG_BLCKSZ-sized buffer */
typedef union PGAlignedXLogBlock
{
char data[XLOG_BLCKSZ];
double force_align_d;
int64 force_align_i64;
} PGAlignedXLogBlock;
/* msb for char */
#define HIGHBIT (0x80)
#define IS_HIGHBIT_SET(ch) ((unsigned char)(ch) & HIGHBIT)