linux-kernel - Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

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Message-ID: <20141007002147.GE23797@brightrain.aerifal.cx>
Date:	Mon, 6 Oct 2014 20:21:47 -0400
From:	Rich Felker <dalias@...c.org>
To:	Andrew Pinski <pinskia@...il.com>
Cc:	David Daney <ddaney@...iumnetworks.com>,
	Andy Lutomirski <luto@...capital.net>,
	David Daney <ddaney.cavm@...il.com>,
	GNU C Library <libc-alpha@...rceware.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mips@...ux-mips.org,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

On Mon, Oct 06, 2014 at 05:11:38PM -0700, Andrew Pinski wrote:
> On Mon, Oct 6, 2014 at 5:05 PM, Rich Felker <dalias@...c.org> wrote:
> > On Mon, Oct 06, 2014 at 04:48:52PM -0700, David Daney wrote:
> >> On 10/06/2014 04:38 PM, Andy Lutomirski wrote:
> >> >On 10/06/2014 02:58 PM, Rich Felker wrote:
> >> >>On Mon, Oct 06, 2014 at 02:45:29PM -0700, David Daney wrote:
> >> [...]
> >> >>This is a huge ill-designed mess.
> >> >
> >> >Amen.
> >> >
> >> >Can the kernel not just emulate the instructions directly?
> >>
> >> In theory it could, but since there can be implementation defined
> >> instructions, there is no way to achieve full instruction set
> >> coverage for all possible machines.
> >
> > Is the issue really implementation-defined instructions with delay
> > slots? If so it sounds like a made-up issue. They're not going to
> > occur in real binaries. Certainly a compiler is not going to generate
> > implementation-defined instructions, and if you're writing the asm by
> > hand, you just don't put floating point instructions in the delay
> > slot.
> 
> It is not the instruction with delay slot but rather the instruction
> in the delay slot itself.

An instruction in the delay slot for the instruction being emulated?
How would that arise? Are there floating point instructions with delay
slots?

Rich
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