linux-kernel - Re: [RFC] x86: Disable traditional FPU instructions too

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Message-ID: <30d5350d-2f0d-4103-a28d-cb9b796fd8ce@email.android.com>
Date:	Tue, 28 Jan 2014 02:25:09 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Michal Hocko <mhocko@...e.cz>, Borislav Petkov <bp@...en8.de>
CC:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Kosina <jkosina@...e.cz>, Michael Matz <matz@...e.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [RFC] x86: Disable traditional FPU instructions too

If that is intentional it needs a big huge freaking comment recording why it is not a bug.  I would expect that to generate a FP multiply.

On January 28, 2014 1:37:01 AM PST, Michal Hocko <mhocko@...e.cz> wrote:
>[CCing Ralf for MIPS.]
>
>On Mon 27-01-14 17:45:44, Borislav Petkov wrote:
>> On Mon, Jan 27, 2014 at 08:41:09AM -0800, H. Peter Anvin wrote:
>> > I don't think it'd hurt... although I think the above pretty much
>> > requires that the code contain actual floating-point types to ever
>be
>> > generated.
>> 
>> Yes, that is supposed to catch usage of the 'E' floating constant,
>for
>> example, in definitions. It is a build-time assertion, if you want.
>:)
>
>And git grep says that mips abuses this notation:
>arch/mips/include/asm/kvm_host.h:#define MS_TO_NS(x) (x * 1E6L)
>
>I do not have cross-compiler set up to check whether this is a real
>issue because include/media/rc-core.h defines the same macro correctly
>so the real code might end up using the right variant.

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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