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@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409160804.eSg9zh1e-lkp@intel.com/
Signed-off-by: Gary Guo <gary@garyguo.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

On Mon, Sep 16, 2024 at 1:09 PM Gary Guo <gary@garyguo.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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202409160804.eSg9zh1e-lkp@intel.com/
> Signed-off-by: Gary Guo <gary@garyguo.net>

Applied to `rust-fixes` -- thanks!

Cheers,
Miguel

On 16.09.24 2:33 AM, Gary Guo 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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202409160804.eSg9zh1e-lkp@intel.com/
> Signed-off-by: Gary Guo <gary@garyguo.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

This is also needed for 32-bit ARM support.

Reviewed-by: Christian Schrefl <chrisi.schrefl@gmail.com>