linux-kernel - Re: [PATCH net-next v5 06/20] zinc: ChaCha20 MIPS32r2 implementation

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Message-ID: <CAHmME9rm9dqa6wtBDLngdXfv+3DCCsgM51z9nbGg3Bb_Q_zdwg@mail.gmail.com>
Date:   Thu, 20 Sep 2018 15:19:06 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     paul.burton@...s.com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        René van Dorst <opensource@...rst.com>,
        Samuel Neves <sneves@....uc.pt>,
        Andrew Lutomirski <luto@...nel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        Ralf Baechle <ralf@...ux-mips.org>, jhogan@...nel.org,
        linux-mips@...ux-mips.org
Subject: Re: [PATCH net-next v5 06/20] zinc: ChaCha20 MIPS32r2 implementation

Hi Paul,

Thanks a bunch for the review.

On Tue, Sep 18, 2018 at 10:25 PM Paul Burton <paul.burton@...s.com> wrote:
> Should this be .set reorder?

Nice catch. Fixed here:
https://git.zx2c4.com/WireGuard/commit/?id=23d97fc333cf85dd07445a9d21a28cbef47c553c
But then...

> Even better - could we not just place the addiu before the bne & drop
> the .set noreorder, allowing the assembler to fill the delay slot with
> the addiu? Likewise in many other places throughout the patch.
>
> That would be more future proof - particularly if we ever want to adjust
> this for use with the nanoMIPS ISA which has no delay slots. It may also
> allow the assembler the choice to use compact branches (ie. branches
> without visible delay slots) when targeting MIPS32r6. I know neither of
> these will currently build this code, but I think avoiding all the
> noreorder blocks would be a nice cleanup just for the sake of
> readability anyway.

Great idea. Rene has committed that here:
https://git.zx2c4.com/WireGuard/commit/?id=5c153a59ac3aa58a3ff17c69fee63d599e5f2758

These will be in the v6 patchset whenever that's posted, and it's
already been merged into the dev tree:
https://git.kernel.org/pub/scm/linux/kernel/git/zx2c4/linux.git/log/?h=jd/wireguard

Regards,
Jason