linux-kernel - [PATCH 1/3] arch/x86: Use offsetof

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Message-ID: <Pine.LNX.4.58.0712261712450.1185@pc-041.diku.dk>
Date:	Wed, 26 Dec 2007 17:13:50 +0100 (MET)
From:	Julia Lawall <julia@...u.dk>
To:	tglx@...utronix.de, viro@....linux.org.uk,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH 1/3] arch/x86: Use offsetof

From: Julia Lawall <julia@...u.dk>

In the patch cc154ac64aa8d3396b187f64cef01ce67f433324, Al Viro observed
that the proper way to compute the distance between two structure fields is
to use offsetof() or a cast to a pointer to character.  The same change can
be applied to a few more files.

The change was made using the following semantic patch
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@r@
type T;
T s;
type T1, T2;
identifier fld1, fld2;
typedef uint8_t;
typedef u8;
@@

(
  (char *)&s.fld1 - (char *)&s.fld2
|
  (uint8_t *)&s.fld1 - (uint8_t *)&s.fld2
|
  (u8 *)&s.fld1 - (u8 *)&s.fld2
|
- (T1)&s.fld1 - (T2)&s.fld2
+ offsetof(T,fld1) - offsetof(T,fld2)
)
// </smpl>

Signed-off-by: Julia Lawall <julia@...u.dk>
---

diff -u -p a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
--- a/arch/x86/kernel/vm86_32.c	2007-10-22 11:25:00.000000000 +0200
+++ b/arch/x86/kernel/vm86_32.c	2007-12-26 16:27:15.000000000 +0100
@@ -215,7 +215,9 @@ asmlinkage int sys_vm86old(struct pt_reg
 	ret = -EFAULT;
 	if (tmp)
 		goto out;
-	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
+	memset(&info.vm86plus, 0,
+	       offsetof(struct kernel_vm86_struct, regs32) -
+	       offsetof(struct kernel_vm86_struct, vm86plus));
 	info.regs32 = &regs;
 	tsk->thread.vm86_info = v86;
 	do_sys_vm86(&info, tsk);
--
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