In pageinspect/hashfuncs.c, avoid crashes on alignment-picky machines.

On machines with MAXALIGN = 8, the payload of a bytea is not maxaligned,
since it will start 4 bytes into a palloc'd value.  On alignment-picky
hardware, this will cause failures in accesses to 8-byte-wide values
within the page.  We already encountered this problem when we introduced
GIN index inspection functions, and fixed it in commit 84ad68d64.  Make
use of the same function for hash indexes.

A small difficulty is that up to now contrib/pageinspect has not shared
any functions at all across files.  To support that, introduce a common
header file "pageinspect.h" for the module.

Also, move get_page_from_raw() out of ginfuncs.c, where it didn't
especially belong, and put it in rawpage.c which seems a more natural home.

Per buildfarm.

Discussion: https://postgr.es/m/17311.1486134714@sss.pgh.pa.us

contrib/pageinspect/brinfuncs.c

@@ -9,6 +9,8 @@
  */
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/htup_details.h"
 #include "access/brin.h"
 #include "access/brin_internal.h"

contrib/pageinspect/btreefuncs.c

@@ -27,6 +27,8 @@
 
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/nbtree.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_am.h"

contrib/pageinspect/fsmfuncs.c

@@ -19,6 +19,8 @@
 
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "funcapi.h"
 #include "lib/stringinfo.h"
 #include "miscadmin.h"

contrib/pageinspect/ginfuncs.c

@@ -9,6 +9,8 @@
  */
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/gin.h"
 #include "access/gin_private.h"
 #include "access/htup_details.h"
@@ -29,26 +31,6 @@ PG_FUNCTION_INFO_V1(gin_page_opaque_info);
 PG_FUNCTION_INFO_V1(gin_leafpage_items);
 
 
-static Page
-get_page_from_raw(bytea *raw_page)
-{
-	int			raw_page_size;
-	Page		page;
-
-	raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
-	if (raw_page_size < BLCKSZ)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("input page too small (%d bytes)", raw_page_size)));
-
-	/* make a copy so that the page is properly aligned for struct access */
-	page = palloc(raw_page_size);
-	memcpy(page, VARDATA(raw_page), raw_page_size);
-
-	return page;
-}
-
-
 Datum
 gin_metapage_info(PG_FUNCTION_ARGS)
 {

contrib/pageinspect/hashfuncs.c

@@ -10,6 +10,8 @@
 
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/hash.h"
 #include "access/htup_details.h"
 #include "catalog/pg_type.h"
@@ -48,27 +50,15 @@ typedef struct HashPageStat
 
 /*
  * Verify that the given bytea contains a HASH page, or die in the attempt.
- * A pointer to the page is returned.
+ * A pointer to a palloc'd, properly aligned copy of the page is returned.
  */
 static Page
 verify_hash_page(bytea *raw_page, int flags)
 {
-	Page		page;
+	Page		page = get_page_from_raw(raw_page);
-	int			raw_page_size;
 	int			pagetype;
 	HashPageOpaque pageopaque;
 
-	raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
-
-	if (raw_page_size != BLCKSZ)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("invalid page size"),
-				 errdetail("Expected size %d, got %d",
-						   BLCKSZ, raw_page_size)));
-
-	page = VARDATA(raw_page);
-
 	if (PageIsNew(page))
 		ereport(ERROR,
 				(errcode(ERRCODE_INDEX_CORRUPTED),

contrib/pageinspect/heapfuncs.c

@@ -25,6 +25,8 @@
 
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/htup_details.h"
 #include "funcapi.h"
 #include "catalog/pg_type.h"

contrib/pageinspect/pageinspect.h

@@ -0,0 +1,21 @@
+/*-------------------------------------------------------------------------
+ *
+ * pageinspect.h
+ *	  Common functions for pageinspect.
+ *
+ * Copyright (c) 2017, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  contrib/pageinspect/pageinspect.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef _PAGEINSPECT_H_
+#define _PAGEINSPECT_H_
+
+#include "storage/bufpage.h"
+
+/* in rawpage.c */
+extern Page get_page_from_raw(bytea *raw_page);
+
+#endif   /* _PAGEINSPECT_H_ */

contrib/pageinspect/rawpage.c

@@ -15,6 +15,8 @@
 
 #include "postgres.h"
 
+#include "pageinspect.h"
+
 #include "access/htup_details.h"
 #include "catalog/catalog.h"
 #include "catalog/namespace.h"
@@ -158,6 +160,42 @@ get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
 	return raw_page;
 }
 
+
+/*
+ * get_page_from_raw
+ *
+ * Get a palloc'd, maxalign'ed page image from the result of get_raw_page()
+ *
+ * On machines with MAXALIGN = 8, the payload of a bytea is not maxaligned,
+ * since it will start 4 bytes into a palloc'd value.  On alignment-picky
+ * machines, this will cause failures in accesses to 8-byte-wide values
+ * within the page.  We don't need to worry if accessing only 4-byte or
+ * smaller fields, but when examining a struct that contains 8-byte fields,
+ * use this function for safety.
+ */
+Page
+get_page_from_raw(bytea *raw_page)
+{
+	Page		page;
+	int			raw_page_size;
+
+	raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
+
+	if (raw_page_size != BLCKSZ)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("invalid page size"),
+				 errdetail("Expected %d bytes, got %d.",
+						   BLCKSZ, raw_page_size)));
+
+	page = palloc(raw_page_size);
+
+	memcpy(page, VARDATA(raw_page), raw_page_size);
+
+	return page;
+}
+
+
 /*
  * page_header
  *