linux-kernel - Re: [PATCH v4 16/20] Kbuild: add Rust support

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Message-ID: <YgfBUhYdLXA46kOX@shell.armlinux.org.uk>
Date:   Sat, 12 Feb 2022 14:16:50 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.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>,
        Daniel Xu <dxu@...uu.xyz>, Miguel Cano <macanroj@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kbuild@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 16/20] Kbuild: add Rust support

On Sat, Feb 12, 2022 at 02:03:42PM +0100, Miguel Ojeda wrote:
> +config RUST
> +	bool "Rust support"
> +	depends on RUST_IS_AVAILABLE
> +	depends on ARM64 || CPU_32v6 || CPU_32v6K || (PPC64 && CPU_LITTLE_ENDIAN) || X86_64 || RISCV

Please don't use CPU_32v6* here.

It probably makes more sense to add a symbol "HAVE_RUST" and have the
appropriate architecture Kconfig files select HAVE_RUST.

Does Rust support Thumb on ARMv6 and ARMv7 architectures?

> +	depends on !MODVERSIONS
> +	depends on !GCC_PLUGIN_RANDSTRUCT
> +	select CONSTRUCTORS
> +	default n

Please remove every utterance of "default n" from your patch; n is the
default default which default defaults to, so you don't need to specify
default n to make the option default to n. It will default to n purely
because n is the default when no default is specified.

> +	help
> +	  Enables Rust support in the kernel.
> +
> +	  This allows other Rust-related options, like drivers written in Rust,
> +	  to be selected.

As Rust doesn't support all the architectures that the kernel supports,
Rust must not be used for core infrastructure.

-- 
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