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Fix alignment problem with bbsink_copystream buffer.

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bbsink_copystream wants to store a type byte just before the buffer,
but basebackup.c wants the buffer to be aligned so that it can call
PageIsNew() and PageGetLSN() on it. Therefore, instead of inserting
1 extra byte before the buffer, insert MAXIMUM_ALIGNOF extra bytes
and only use the last one.

On most machines this doesn't cause any problem (except perhaps for
performance) but some buildfarm machines with -fsanitize=alignment
dump core.

Discussion: http://postgr.es/m/CA+TgmoYx5=1A2K9JYV-9zdhyokU4KKTyNQ9q7CiXrX=YBBMWVw@mail.gmail.com
This commit is contained in:
Robert Haas 2022-01-19 08:07:16 -05:00
parent 44129c0432
commit 0f47e833bf
1 changed files with 11 additions and 7 deletions
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18
src/backend/replication/basebackup_copy.c
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@ -152,18 +152,22 @@ bbsink_copystream_begin_backup(bbsink *sink)
{
bbsink_copystream *mysink = (bbsink_copystream *) sink;
bbsink_state *state = sink->bbs_state;
char *buf;
/*
* Initialize buffer. We ultimately want to send the archive and manifest
* data by means of CopyData messages where the payload portion of each
* message begins with a type byte, so we set up a buffer that begins with
* a the type byte we're going to need, and then arrange things so that
* the data we're given will be written just after that type byte. That
* will allow us to ship the data with a single call to pq_putmessage and
* without needing any extra copying.
* message begins with a type byte. However, basebackup.c expects the
* buffer to be aligned, so we can't just allocate one extra byte for the
* type byte. Instead, allocate enough extra bytes that the portion of
* the buffer we reveal to our callers can be aligned, while leaving room
* to slip the type byte in just beforehand. That will allow us to ship
* the data with a single call to pq_putmessage and without needing any
* extra copying.
*/
mysink->msgbuffer = palloc(mysink->base.bbs_buffer_length + 1);
mysink->base.bbs_buffer = mysink->msgbuffer + 1;
buf = palloc(mysink->base.bbs_buffer_length + MAXIMUM_ALIGNOF);
mysink->msgbuffer = buf + (MAXIMUM_ALIGNOF - 1);
mysink->base.bbs_buffer = buf + MAXIMUM_ALIGNOF;
mysink->msgbuffer[0] = 'd'; /* archive or manifest data */
/* Tell client the backup start location. */