linux-kernel - Re: Fixing MIPS delay slot emulation weakness?

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Message-ID: <20181216181137.GF23599@brightrain.aerifal.cx>
Date:   Sun, 16 Dec 2018 13:11:37 -0500
From:   Rich Felker <dalias@...c.org>
To:     Paul Burton <paul.burton@...s.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paul Burton <paul.burton@...tec.com>,
        David Daney <david.daney@...ium.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>
Subject: Re: Fixing MIPS delay slot emulation weakness?

On Sat, Dec 15, 2018 at 09:26:45PM +0000, Paul Burton wrote:
> > The really nice but less compatible fix would be to let processes or
> > even the whole system opt out by promising not to put anything in FPU
> > branch delay slots, of course.
> 
> The ultimate fix comes with a switch to the nanoMIPS ISA which has no
> delay slots :)

I don't understand the MIPS position that introducing new ISAs
(including silently-new like r6) and not supporting or deprecating
support for the old one is a solution to anything. If one doesn't care
about the ability to run existing binaries for your platform, one
might as well switch to RISC-V or ARM or whatever. The whole advantage
of an ISA as a "platform" is the ability to run existing software and
use existing tooling (not just compilers; think also JITs, FFI
frameworks, etc), not any particular design advantage the ISA has.

Rich