From: Greg Stark <stark@mit.edu>
Date: Thu, 2 Jun 2016 18:23:25 +0000 (+0100)
Subject: Be conservative about alignment requirements of struct epoll_event.
X-Git-Tag: REL9_6_BETA2~124
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a3b30763cc8686f5b4cd121ef0bf510c1533ac22;p=thirdparty%2Fpostgresql.git

Be conservative about alignment requirements of struct epoll_event.

Use MAXALIGN size/alignment to guarantee that later uses of memory are
aligned correctly. E.g. epoll_event might need 8 byte alignment on some
platforms, but earlier allocations like WaitEventSet and WaitEvent might
not sized to guarantee that when purely using sizeof().

Found by myself while testing on an Sun Ultra 5 (Sparc IIi) with some
editorializing by Andres Freund.

In passing fix a couple typos in the area
---

diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index 3fbe0e50795..7d8ad63feb3 100644
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -475,7 +475,7 @@ ResetLatch(volatile Latch *latch)
 /*
  * Create a WaitEventSet with space for nevents different events to wait for.
  *
- * These events can then efficiently waited upon together, using
+ * These events can then be efficiently waited upon together, using
  * WaitEventSetWait().
  */
 WaitEventSet *
@@ -485,35 +485,41 @@ CreateWaitEventSet(MemoryContext context, int nevents)
 	char	   *data;
 	Size		sz = 0;
 
-	sz += sizeof(WaitEventSet);
-	sz += sizeof(WaitEvent) * nevents;
+	/* 
+	 * Use MAXALIGN size/alignment to guarantee that later uses of memory are
+	 * aligned correctly. E.g. epoll_event might need 8 byte alignment on some
+	 * platforms, but earlier allocations like WaitEventSet and WaitEvent
+	 * might not sized to guarantee that when purely using sizeof().
+	 */
+	sz += MAXALIGN(sizeof(WaitEventSet));
+	sz += MAXALIGN(sizeof(WaitEvent) * nevents);
 
 #if defined(WAIT_USE_EPOLL)
-	sz += sizeof(struct epoll_event) * nevents;
+	sz += MAXALIGN(sizeof(struct epoll_event) * nevents);
 #elif defined(WAIT_USE_POLL)
-	sz += sizeof(struct pollfd) * nevents;
+	sz += MAXALIGN(sizeof(struct pollfd) * nevents);
 #elif defined(WAIT_USE_WIN32)
 	/* need space for the pgwin32_signal_event */
-	sz += sizeof(HANDLE) * (nevents + 1);
+	sz += MAXALIGN(sizeof(HANDLE) * (nevents + 1));
 #endif
 
 	data = (char *) MemoryContextAllocZero(context, sz);
 
 	set = (WaitEventSet *) data;
-	data += sizeof(WaitEventSet);
+	data += MAXALIGN(sizeof(WaitEventSet));
 
 	set->events = (WaitEvent *) data;
-	data += sizeof(WaitEvent) * nevents;
+	data += MAXALIGN(sizeof(WaitEvent) * nevents);
 
 #if defined(WAIT_USE_EPOLL)
 	set->epoll_ret_events = (struct epoll_event *) data;
-	data += sizeof(struct epoll_event) * nevents;
+	data += MAXALIGN(sizeof(struct epoll_event) * nevents);
 #elif defined(WAIT_USE_POLL)
 	set->pollfds = (struct pollfd *) data;
-	data += sizeof(struct pollfd) * nevents;
+	data += MAXALIGN(sizeof(struct pollfd) * nevents);
 #elif defined(WAIT_USE_WIN32)
 	set->handles = (HANDLE) data;
-	data += sizeof(HANDLE) * nevents;
+	data += MAXALIGN(sizeof(HANDLE) * nevents);
 #endif
 
 	set->latch = NULL;
@@ -616,7 +622,7 @@ AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd, Latch *latch,
 		if (set->latch)
 			elog(ERROR, "cannot wait on more than one latch");
 		if ((events & WL_LATCH_SET) != WL_LATCH_SET)
-			elog(ERROR, "latch events only spuport being set");
+			elog(ERROR, "latch events only support being set");
 	}
 	else
 	{