linux-kernel - Re: [RFC] x86: xsave/xrstor support, ucontext

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Message-ID: <4833118D.5050001@zytor.com>
Date:	Tue, 20 May 2008 10:59:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>, mingo@...e.hu,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, roland@...hat.com, drepper@...hat.com,
	Hongjiu.lu@...el.com, linux-kernel@...r.kernel.org,
	arjan@...ux.intel.com, rmk+lkml@....linux.org.uk, dan@...ian.org,
	asit.k.mallick@...el.com
Subject: Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

Suresh Siddha wrote:
> 
> This issue of not-zeroing, is present in only 64bit kernels and for 64bit apps,
> right?
> 
> 64bit app signal handling uses only rt_frame, so we can add an uc_flag for
> them and for 32bit apps, kernel was always zero'ing the reserved bits
> at the end of _fpstate.
> 
> In short, for non-rt frames, they can check the reserved bits at the end
> of fpstate frame and for rt-frames (perhaps even for 32bit rt frame handling)
> apps can check for uc_flag aswell, for extended state presence. Is this
> good enough?
> 

Are we sure about the "always" bit here (I suspect yes, but we may want 
to double-check at least back to 2.2 or 2.4.)

Anyway, seems reasonable enough to me.

	-hpa
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