linux-kernel - Re: [PATCH v4 3/7] mips: rename macros and files from '64' to 'n64'

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Message-ID: <20181210234620.rcmapky2aj7eb2wh@pburton-laptop>
Date:   Mon, 10 Dec 2018 23:46:21 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
CC:     Firoz Khan <firoz.khan@...aro.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "y2038@...ts.linaro.org" <y2038@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "deepa.kernel@...il.com" <deepa.kernel@...il.com>,
        "marcin.juszkiewicz@...aro.org" <marcin.juszkiewicz@...aro.org>
Subject: Re: [PATCH v4 3/7] mips: rename macros and files from '64' to 'n64'

Hi Maciej,

On Mon, Dec 10, 2018 at 11:32:46PM +0000, Maciej W. Rozycki wrote:
> On Mon, 10 Dec 2018, Paul Burton wrote:
> 
> > And I realise that undoing that but keeping n64 in our own filenames &
> > macros is another type of inconsistency, but something imperfect is
> > unavoidable at this point given that the engineers way back when decided
> > to use "ABI64" for n64.
> 
>  My feeling has been n32 was invented at SGI as an afterthought, hence the 
> choice of having ABI32 or ABI64 defined for the 32-bit (now o32) and the 
> 64-bit (now n64) ABI respectively was reasonable.

I'd agree if _MIPS_SIM were defined as _ABI32 for o32, but:

  $ mips-linux-gcc -mabi=32 -dM -E - </dev/null | grep ABIO32
  #define _ABIO32 1
  #define _MIPS_SIM _ABIO32

...so _MIPS_SIM is:

  _ABIO32 for o32
  _ABIN32 for n32
  _ABI64 for n64

That doesn't seem very consistent to me, and means that there inevitably
has to be some ugliness once there are multiple 64-bit ABIs.

To me it feels like the result of someone thinking "one 64-bit MIPS ABI
ought to be enough for anybody". I'm undecided whether that person was
shortsighted or a genius whose vision was simply incomprehensible to
those of us that followed.

Thanks,
    Paul