linux-kernel - Re: [PATCH 0/3] System call table generation support

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Message-ID: <20180921060941.GB13865@infradead.org>
Date:   Thu, 20 Sep 2018 23:09:41 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Paul Burton <paul.burton@...s.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Firoz Khan <firoz.khan@...aro.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <zajec5@...il.com>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>
Subject: Re: [PATCH 0/3] System call table generation support

On Thu, Sep 20, 2018 at 08:48:37PM +0000, Paul Burton wrote:
> > Speaking of nanoMIPS, what is your plan for the syscall ABI there?
> > I can see two ways of approaching it:
> > 
> > a) keep all the MIPSisms in the data structures, and just use a subset of
> >     o32 that drops all the obsolete entry points
> > b) start over and stay as close as possible to the generic ABI, using the
> >     asm-generic versions of both the syscall table and the uapi header
> >     files instead of the traditional version.
> 
> We've taken option b in our current downstream kernel & that's what I
> hope we'll get upstream too. There's no expectation that we'll ever need
> to mix pre-nanoMIPS & nanoMIPS ISAs or their associated ABIs across the
> kernel/user boundary so it's felt like a great opportunity to clean up &
> standardise.
> 
> Getting nanoMIPS/p32 support submitted upstream is on my to-do list, but
> there's a bunch of prep work to get in first & of course that to-do list
> is forever growing. Hopefully in the next couple of cycles.

p32 is just the ABI name for nanoMIPS or yet another MIPS ABI?

Either way, І think if there is yet another ABI even on an existing port
we should always aim for the asm-generic syscall table indeed.

Especially for mips where o32 has a rather awkward ABI only explained by
odd decisions more than 20 years ago.