linux-kernel - Re: [PATCH v7 21/25] Kbuild: add Rust support

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Message-ID: <CANiq72=QJsScPweqWO8w6t4wDKKd3ZWFkA6Dcto6qpJ8QcfgOg@mail.gmail.com>
Date:   Tue, 24 May 2022 17:12:00 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux <rust-for-linux@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Finn Behrens <me@...enk.de>,
        Adam Bratschi-Kaye <ark.email@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sven Van Asbroeck <thesven73@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Boris-Chengbiao Zhou <bobo1239@....de>,
        Boqun Feng <boqun.feng@...il.com>,
        Douglas Su <d0u9.su@...look.com>,
        Dariusz Sosnowski <dsosnowski@...snowski.pl>,
        Antonio Terceiro <antonio.terceiro@...aro.org>,
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        Dave Hansen <dave.hansen@...ux.intel.com>,
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        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-um@...ts.infradead.org
Subject: Re: [PATCH v7 21/25] Kbuild: add Rust support

On Mon, May 23, 2022 at 8:45 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> I'm super not into having the rust optimization level differ from the
> C optimization level.  This is just someone having too much fun
> wrapping every compiler flag in a kbuild option.  Either folks wan't

I mean, `Makefile`s are not my favorite pastime... :)

> smaller size or more optimizations. Allowing for RUST_OPT_LEVEL_S and
> CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE or RUST_OPT_LEVEL_3 and
> CONFIG_CC_OPTIMIZE_FOR_SIZE is just wacky nonsense that's going to
> make randconfig bug reports more confusing to tease out.

I think what is important is to decide whether extra levels, for C and
Rust, should be kept compile-able/maintained or not (I also replied in
the `-O1` for C thread [1]).

Note that the Rust side can be compiled as `-O0` or `-O1` at the
moment, which is something we do not have for the C side; thus having
only the C == Rust option means we will not have a configuration with
those anymore.

For me it is less complex to not have them, and I have not heard more
opinions on this, either for or against (apart from that thread
suggesting `-O1` for the C side), so if nobody else chimes in, I will
remove them.

[1] https://lore.kernel.org/lkml/CANiq72kySVvOQ7eqwe0Jzz3V0JTtrcqODHR9Ty4-sfDMdzP6XQ@mail.gmail.com/

Cheers,
Miguel