linux-kernel - Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case

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Message-ID: <CA+55aFxfAn9MWRgS3O5k2tqN5ys1XrhSFVO5_9ZAoZKDVgNfGA@mail.gmail.com>
Date:	Mon, 20 Feb 2012 10:03:24 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, a.p.zijlstra@...llo.nl,
	torvalds@...ux-foundation.org, stable@...nel.org,
	tglx@...utronix.de, mingo@...e.hu
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine
 nested NMI case

On Mon, Feb 20, 2012 at 3:47 AM, tip-bot for Steven Rostedt
<rostedt@...dmis.org> wrote:
>        /*
> +        * If %cs was not the kernel segment, then the NMI triggered in user
> +        * space, which means it is definitely not nested.
> +        */
> +       cmp $__KERNEL_CS, 16(%rsp)
> +       jne first_nmi

I don't like how you wrote 'cmp' without a size, especially with none
of the arguments then giving a size either. Usually there's a register
name or something that gives you the size, but not here.

I guess there is some default size that gas will use, but at least
some versions of gas have traditionally errored out instead of
guessing on sizes. Maybe x86-64 doesn't use those gas versions any
more, but still..

                                        Linus
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