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

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Message-ID: <20071230135458.GB21106@elte.hu>
Date:	Sun, 30 Dec 2007 14:54:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>, Pavel Machek <pavel@....cz>,
	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


* H. Peter Anvin <hpa@...or.com> wrote:

>>> The right way to do it is:
>>>
>>> 	memset(&info.vm86plus, 0, sizeof info.vm86plus);
>>
>> If it's just one field _and_ we don't have padding we want to zero out -
>> certainly...
>
> It is - [comments removed for clarity]:
>
> struct kernel_vm86_struct {
>         struct kernel_vm86_regs regs;
> #define VM86_TSS_ESP0 flags
>         unsigned long flags;
>         unsigned long screen_bitmap;
>         unsigned long cpu_type;
>         struct revectored_struct int_revectored;
>         struct revectored_struct int21_revectored;
>         struct vm86plus_info_struct vm86plus;
>         struct pt_regs *regs32;
> };

hm, i'm wondering why it was done in such a complex way. Clearing a 
struct field is always done via sizeof. Maybe we lost some alignment 
assumption somewhere along the line?

	Ingo
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