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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Mon, 17 Jan 2022 05:45:26 +0100
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Subject: Re: [PATCH 15/19] Kbuild: add Rust support
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux <rust-for-linux@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Finn Behrens <me@kloenk.de>,
        Adam Bratschi-Kaye <ark.email@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Sven Van Asbroeck <thesven73@gmail.com>,
        Gary Guo <gary@garyguo.net>,
        Boris-Chengbiao Zhou <bobo1239@web.de>,
        Boqun Feng <boqun.feng@gmail.com>,
        Douglas Su <d0u9.su@outlook.com>,
        Dariusz Sosnowski <dsosnowski@dsosnowski.pl>,
        Antonio Terceiro <antonio.terceiro@linaro.org>,
        Daniel Xu <dxu@dxuuu.xyz>
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Hi Masahiro,

On Sat, Dec 11, 2021 at 4:54 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Do you really want to support CLIPPY=1
> in addition to KBUILD_CLIPPY=1 ?
>
> (Refer to C=  V=  M=  O=, which checks $(origin ) )

I implemented both because I saw the pattern used for `V=`, `W=` etc.,
and I thought I should follow it too. If I understand correctly, the
split between `KBUILD_*` and the shorthands is there to avoid
conflicts if the caller had set very short environment variables for
some reason -- is this correct?

If you prefer only one, I think writing `KBUILD_CLIPPY=1` would be too
long for command line usage; so I would prefer `CLIPPY=1` in that
case.

> Is there any reason why
> you did not write like
>
>   core-$(CONFIG_RUST)  += rust/
>
> ?

I have moved it inside the `rust/Makefile` -- please take a look at
the next round I am sending in a bit.

> extra-y does nothing for 'make modules'.
> Is this your expected behavior?
>
> (commit d0e628cd817f3)

Thanks for the reference! Changed to `always-y`. Indeed, this is
needed in `make modules` because we need to trigger the compilation of
`core.o` etc. for the `.rmeta` files.

> Why is .SECONDEXPANSION: needed ?

It was needed at some point for the prototype more than a year ago;
however, it isn't the case anymore, so I have removed it. I have also
made those variables simply expanded ones.

Cheers,
Miguel