linux-kernel - Re: [PATCH] rust: fix `ARCH_SLAB_MINALIGN` multiple definition error

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Message-ID: <CANiq72=qRGkXJoTin69KDgz0YHDaY8uB0vfX=GDZeR7TbhaTdA@mail.gmail.com>
Date: Thu, 26 Sep 2024 23:18:50 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Gary Guo <gary@...yguo.net>
Cc: lkp@...el.com, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, conor.dooley@...rochip.com, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	oe-kbuild-all@...ts.linux.dev, palmer@...osinc.com, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH] rust: fix `ARCH_SLAB_MINALIGN` multiple definition error

On Mon, Sep 16, 2024 at 1:09 PM Gary Guo <gary@...yguo.net> wrote:
>
> We use const helpers in form of
>
>     const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
>
> to aid generation of constants by bindgen because it is otherwise a
> macro definition of an expression and bindgen doesn't expand the
> constant. The helpers are then have `RUST_CONST_HELPER` prefix stripped
> and exposed to Rust code as if `ARCH_SLAB_MISALIGN` is generated
> natively by bindgen.
>
> This works well for most constants, but on RISC-V, `ARCH_SLAB_MINALIGN`
> is defined directly as literal constant if `!CONFIG_MMU`, and bindgen
> would generate `ARCH_SLAB_MINALIGN` directly, thus conflict with the
> one generated through the helper.
>
> To fix this, we simply need to block bindgen from generating directly
> without going through helper.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202409160804.eSg9zh1e-lkp@intel.com/
> Signed-off-by: Gary Guo <gary@...yguo.net>

Applied to `rust-fixes` -- thanks!

Cheers,
Miguel