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

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Message-ID: <20240916003347.1744345-1-gary@garyguo.net>
Date: Mon, 16 Sep 2024 01:33:46 +0100
From: Gary Guo <gary@...yguo.net>
To: 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>,
	Gary Guo <gary@...yguo.net>,
	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>
Cc: 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: [PATCH] rust: fix `ARCH_SLAB_MINALIGN` multiple definition error

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>
---
 rust/bindgen_parameters | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/rust/bindgen_parameters b/rust/bindgen_parameters
index a721d466bee4b..b7c7483123b7a 100644
--- a/rust/bindgen_parameters
+++ b/rust/bindgen_parameters
@@ -24,3 +24,8 @@
 # These functions use the `__preserve_most` calling convention, which neither bindgen
 # nor Rust currently understand, and which Clang currently declares to be unstable.
 --blocklist-function __list_.*_report
+
+# These constants are sometimes not recognized by bindgen depending on config.
+# We use const helpers to aid bindgen, to avoid conflicts when constants are
+# recognized, block generation of the non-helper constants.
+--blocklist-item ARCH_SLAB_MINALIGN

base-commit: d077242d68a31075ef5f5da041bf8f6fc19aa231
-- 
2.44.1