linux-kernel - Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

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Date:	Fri, 2 Mar 2007 20:48:54 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Nicholas Miell <nmiell@...cast.net>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

On Fri, Mar 02, 2007 at 05:36:01PM -0800, Nicholas Miell wrote:
> > as an asynchronous context helps alot: the classic gcc convention for 
> > FPU use & function calls should apply: gcc does not call an external 
> > function with an in-use FPU stack/register, it always neatly unuses it, 
> > as no FPU register is callee-saved, all are caller-saved.
> 
> The i386 psABI is ancient (i.e. it predates SSE, so no mention of the
> XMM or MXCSR registers) and a bit vague (no mention at all of the FP
> status word), but I'm fairly certain that Ingo is right.

The FPU status word *must* be saved, as the rounding behaviour and error mode 
bits are assumed to be preserved.  Iow, yes, there is state which is required.

		-ben
-- 
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