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

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Message-ID: <20141007192107.GN23797@brightrain.aerifal.cx>
Date:	Tue, 7 Oct 2014 15:21:07 -0400
From:	Rich Felker <dalias@...c.org>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Matthew Fortune <Matthew.Fortune@...tec.com>,
	David Daney <david.s.daney@...il.com>,
	David Daney <ddaney@...iumnetworks.com>,
	David Daney <ddaney.cavm@...il.com>,
	"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mips@...ux-mips.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 Tue, Oct 07, 2014 at 12:16:59PM -0700, Leonid Yegoshin wrote:
> On 10/07/2014 12:09 PM, Rich Felker wrote:
> >I agree completely here. We should not break things (or, as it
> >seems, leave them broken) for common usage cases that affect
> >everyone just to coddle proprietary vendor-specific instructions.
> >The latter just should not be used in delay slots unless the chip
> >vendor also promises to provide fpu branch in hardware. Rich
> And what do you propose - remove a current in-stack emulation and
> you still think it doesn't break a status-quo?

The in-stack trampoline support could be left but used only for
emulating instructions the kernel doesn't know. This would make all
normal binaries immediately usable with non-executable stack, and
would avoid the only potential source of regressions. Ultimately I
think the "xol" stuff should be removed, but that could be a long term
goal.

Rich
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