From: Robert Haas Date: Wed, 19 Jan 2022 13:07:16 +0000 (-0500) Subject: Fix alignment problem with bbsink_copystream buffer. X-Git-Tag: REL_15_BETA1~874 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0f47e833bf6d96c1a2c5173c8e0f6c6cc30f9592;p=thirdparty%2Fpostgresql.git Fix alignment problem with bbsink_copystream buffer. 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 --- diff --git a/src/backend/replication/basebackup_copy.c b/src/backend/replication/basebackup_copy.c index f42b368c033..8dfdff06449 100644 --- a/src/backend/replication/basebackup_copy.c +++ b/src/backend/replication/basebackup_copy.c @@ -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. */