From dcbbdb1b3ee17bee849f96734f0c40d2b74f2ab5 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 30 Mar 2001 05:25:51 +0000 Subject: [PATCH] Add appropriately ifdef'd hack to make ARM compiler allocate ItemPointerData as six bytes not eight. This fixes a regression test failure but more importantly avoids wasting four bytes of pad space in every tuple header. Also add some commentary about what's going on. --- src/include/storage/itemptr.h | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/src/include/storage/itemptr.h b/src/include/storage/itemptr.h index 5b2c715e01..b26fab11e7 100644 --- a/src/include/storage/itemptr.h +++ b/src/include/storage/itemptr.h @@ -7,7 +7,7 @@ * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $Id: itemptr.h,v 1.17 2001/03/22 04:01:06 momjian Exp $ + * $Id: itemptr.h,v 1.18 2001/03/30 05:25:51 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -20,15 +20,29 @@ /* * ItemPointer: * - * this is a pointer to an item on another disk page in the same file. + * This is a pointer to an item within a disk page of a known file + * (for example, a cross-link from an index to its parent table). * blkid tells us which block, posid tells us which entry in the linp * (ItemIdData) array we want. + * + * Note: because there is an item pointer in each tuple header and index + * tuple header on disk, it's very important not to waste space with + * structure padding bytes. The struct is designed to be six bytes long + * (it contains three int16 fields) but a few compilers will pad it to + * eight bytes unless coerced. We apply appropriate persuasion where + * possible, and to cope with unpersuadable compilers, we try to use + * "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing + * on-disk sizes. */ typedef struct ItemPointerData { BlockIdData ip_blkid; OffsetNumber ip_posid; -} ItemPointerData; +} +#ifdef __arm__ +__attribute__((packed)) /* Appropriate whack upside the head for ARM */ +#endif + ItemPointerData; #define SizeOfIptrData \ (offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber)) -- 2.40.0