On Fri, 27 Sep 2019 at 09:21, Jason A. Donenfeld [off-list ref] wrote:

Hey Andy,

Thanks for weighing in.

quoted

inlining.  I'd be surprised for chacha20.  If you really want inlining
to dictate the overall design, I think you need some real numbers for
why it's necessary.  There also needs to be a clear story for how
exactly making everything inline plays with the actual decision of
which implementation to use.

Take a look at my description for the MIPS case: when on MIPS, the
arch code is *always* used since it's just straight up scalar
assembly. In this case, the chacha20_arch function *never* returns
false [1], which means it's always included [2], so the generic
implementation gets optimized out, saving disk and memory, which I
assume MIPS people care about.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/zx2c4/linux.git/tree/lib/zinc/chacha20/chacha20-mips-glue.c?h=jd/wireguard#n13
[2] https://git.kernel.org/pub/scm/linux/kernel/git/zx2c4/linux.git/tree/lib/zinc/chacha20/chacha20.c?h=jd/wireguard#n118

I'm fine with considering this a form of "premature optimization",
though, and ditching the motivation there.

On Thu, Sep 26, 2019 at 11:37 PM Andy Lutomirski [off-list ref] wrote:

quoted

My suggestion from way back, which is at
least a good deal of the way toward being doable, is to do static
calls.  This means that the common code will call out to the arch code
via a regular CALL instruction and will *not* inline the arch code.
This means that the arch code could live in its own module, it can be
selected at boot time, etc.

Alright, let's do static calls, then, to deal with the case of going
from the entry point implementation in lib/zinc (or lib/crypto, if you
want, Ard) to the arch-specific implementation in arch/${ARCH}/crypto.
And then within each arch, we can keep it simple, since everything is
already in the same directory.

Sound good?

Yup.

I posted something to this effect - I am ironing out some wrinkles
doing randconfig builds (with Arnd's help) but the general picture
shouldn't change.

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