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

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Date:	Fri, 02 Mar 2007 17:36:01 -0800
From:	Nicholas Miell <nmiell@...cast.net>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	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, 2007-03-02 at 16:52 -0800, Davide Libenzi wrote:
> On Fri, 2 Mar 2007, Nicholas Miell wrote:
> 
> > The point Ingo was making is that the x86 ABI already requires the FPU
> > context to be saved before *all* function calls.
> 
> I've not seen that among Ingo's points, but yeah some status is caller 
> saved. But, aren't things like status word and control bits callee saved? 
> If that's the case, it might require proper handling.
> 

Ingo mentioned it in one of the parts you cut out of your reply:

> and here is where thinking about threadlets as a function call and not 
> 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.


-- 
Nicholas Miell <nmiell@...cast.net>

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