From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 25 Mar 2019 08:35:29 +0000 (+0100)
Subject: Add macro to cast away volatile without allowing changes to underlying type
X-Git-Tag: REL_12_BETA1~433
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=481018f2804065cb5ed1cde75b7c0596aeef959a;p=postgresql

Add macro to cast away volatile without allowing changes to underlying type

This adds unvolatize(), which works just like unconstify() but for volatile.

Discussion: https://www.postgresql.org/message-id/flat/7a5cbea7-b8df-e910-0f10-04014bcad701%402ndquadrant.com
---

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 2fbfadd9f0..2a8472b91a 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -3311,7 +3311,7 @@ pgstat_read_current_status(void)
 			localentry->backendStatus.st_procpid = beentry->st_procpid;
 			if (localentry->backendStatus.st_procpid > 0)
 			{
-				memcpy(&localentry->backendStatus, (char *) beentry, sizeof(PgBackendStatus));
+				memcpy(&localentry->backendStatus, unvolatize(PgBackendStatus *, beentry), sizeof(PgBackendStatus));
 
 				/*
 				 * strcpy is safe even if the string is modified concurrently,
diff --git a/src/backend/storage/ipc/pmsignal.c b/src/backend/storage/ipc/pmsignal.c
index d707993bf6..48f4311464 100644
--- a/src/backend/storage/ipc/pmsignal.c
+++ b/src/backend/storage/ipc/pmsignal.c
@@ -134,7 +134,7 @@ PMSignalShmemInit(void)
 
 	if (!found)
 	{
-		MemSet(PMSignalState, 0, PMSignalShmemSize());
+		MemSet(unvolatize(PMSignalData *, PMSignalState), 0, PMSignalShmemSize());
 		PMSignalState->num_child_flags = MaxLivePostmasterChildren();
 	}
 }
diff --git a/src/include/c.h b/src/include/c.h
index 658be50e0d..33c9518195 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -1122,7 +1122,7 @@ typedef union PGAlignedXLogBlock
 #endif
 
 /*
- * Macro that allows to cast constness away from an expression, but doesn't
+ * Macro that allows to cast constness and volatile away from an expression, but doesn't
  * allow changing the underlying type.  Enforcement of the latter
  * currently only works for gcc like compilers.
  *
@@ -1141,9 +1141,15 @@ typedef union PGAlignedXLogBlock
 	(StaticAssertExpr(__builtin_types_compatible_p(__typeof(expr), const underlying_type), \
 					  "wrong cast"), \
 	 (underlying_type) (expr))
+#define unvolatize(underlying_type, expr) \
+	(StaticAssertExpr(__builtin_types_compatible_p(__typeof(expr), volatile underlying_type), \
+					  "wrong cast"), \
+	 (underlying_type) (expr))
 #else
 #define unconstify(underlying_type, expr) \
 	((underlying_type) (expr))
+#define unvolatize(underlying_type, expr) \
+	((underlying_type) (expr))
 #endif
 
 /* ----------------------------------------------------------------