linux-kernel - Re: [GIT PULL] x86 fixes

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Message-ID: <55D453B0.2090108@zytor.com>
Date:	Wed, 19 Aug 2015 03:00:16 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Andy Lutomirski <luto@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86 fixes

On 08/18/15 23:50, Ingo Molnar wrote:
>
> Ah, so I was able to make math-emu work with the 'no387 nofxsr' boot options.
>
> It turns out that the crash happens due 'no387' not turning off all modern FPU
> features in cpufeatures, which confuses the FPU code. (This is a far less severe
> bug than math emu not working at all.)
>
> I get some instances of:
>
>     /etc/rc3.d/S99local: line 26:  1626 Illegal instruction
>
> due to user-space presuming modern FPU capabilities:
>

And I bet if CPUID actually reported the right thing it probably would 
work okay.  As I said, I tested this under Qemu which reported an 
accurate (lack of) CPUID for a 486SX.

	-hpa


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