From 6ab58354df4000372f6b098c3a55fa5a1681569f Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 10 Jun 2011 17:03:21 -0400 Subject: [PATCH] Work around gcc 4.6.0 bug that breaks WAL replay. ReadRecord's habit of using both direct references to tmpRecPtr and references to *RecPtr (which is pointing at tmpRecPtr) triggers an optimization bug in gcc 4.6.0, which apparently has forgotten about aliasing rules. Avoid the compiler bug, and make the code more readable to boot, by getting rid of the direct references. Improve the comments while at it. Back-patch to all supported versions, in case they get built with 4.6.0. Tom Lane, with some cosmetic suggestions from Alex Hunsaker --- src/backend/access/transam/xlog.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 2be97788ca..18af6a597b 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -3041,12 +3041,12 @@ ReadRecord(XLogRecPtr *RecPtr, int emode) goto got_record; } /* align old recptr to next page */ - if (tmpRecPtr.xrecoff % XLOG_BLCKSZ != 0) - tmpRecPtr.xrecoff += (XLOG_BLCKSZ - tmpRecPtr.xrecoff % XLOG_BLCKSZ); - if (tmpRecPtr.xrecoff >= XLogFileSize) + if (RecPtr->xrecoff % XLOG_BLCKSZ != 0) + RecPtr->xrecoff += (XLOG_BLCKSZ - RecPtr->xrecoff % XLOG_BLCKSZ); + if (RecPtr->xrecoff >= XLogFileSize) { - (tmpRecPtr.xlogid)++; - tmpRecPtr.xrecoff = 0; + (RecPtr->xlogid)++; + RecPtr->xrecoff = 0; } /* We will account for page header size below */ } @@ -3132,11 +3132,13 @@ ReadRecord(XLogRecPtr *RecPtr, int emode) if (targetRecOff == 0) { /* - * Can only get here in the continuing-from-prev-page case, because - * XRecOffIsValid eliminated the zero-page-offset case otherwise. Need - * to skip over the new page's header. + * At page start, so skip over page header. The Assert checks that + * we're not scribbling on caller's record pointer; it's OK because we + * can only get here in the continuing-from-prev-record case, since + * XRecOffIsValid rejected the zero-page-offset case otherwise. */ - tmpRecPtr.xrecoff += pageHeaderSize; + Assert(RecPtr == &tmpRecPtr); + RecPtr->xrecoff += pageHeaderSize; targetRecOff = pageHeaderSize; } else if (targetRecOff < pageHeaderSize) -- 2.40.0