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

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Message-ID: <4772F972.7070802@zytor.com>
Date:	Wed, 26 Dec 2007 17:01:38 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pavel Machek <pavel@....cz>
CC:	Julia Lawall <julia@...u.dk>, tglx@...utronix.de,
	viro@....linux.org.uk, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/3] arch/x86: Use offsetof

Pavel Machek wrote:
>>
>> 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));
> 
> I do not think this makes it more readable... (int) -> (char *) would
> make it portable and readable, AFAICT.
> 								Pavel

The right way to do it is:

	memset(&info.vm86plus, 0, sizeof info.vm86plus);

	-hpa
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