1 files changed, 26 insertions, 0 deletions
diff --git a/src/include/c.h b/src/include/c.h
index 1e50103095b..901d7911980 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -989,6 +989,32 @@ extern void ExceptionalCondition(const char *conditionName,
  * ----------------------------------------------------------------
  */
 
+/*
+ * Use this, not "char buf[BLCKSZ]", to declare a field or local variable
+ * holding a page buffer, if that page might be accessed as a page and not
+ * just a string of bytes.  Otherwise the variable might be under-aligned,
+ * causing problems on alignment-picky hardware.  (In some places, we use
+ * this to declare buffers even though we only pass them to read() and
+ * write(), because copying to/from aligned buffers is usually faster than
+ * using unaligned buffers.)  We include both "double" and "int64" in the
+ * union to ensure that the compiler knows the value must be MAXALIGN'ed
+ * (cf. configure's computation of MAXIMUM_ALIGNOF).
+ */
+typedef union PGAlignedBlock
+{
+	char		data[BLCKSZ];
+	double		force_align_d;
+	int64		force_align_i64;
+} PGAlignedBlock;
+
+/* Same, but for an XLOG_BLCKSZ-sized buffer */
+typedef union PGAlignedXLogBlock
+{
+	char		data[XLOG_BLCKSZ];
+	double		force_align_d;
+	int64		force_align_i64;
+} PGAlignedXLogBlock;
+
 /* msb for char */
 #define HIGHBIT					(0x80)
 #define IS_HIGHBIT_SET(ch)		((unsigned char)(ch) & HIGHBIT)