Re: [PATCH 31/33] rust: declare cfi_encoding for lru_status

[Gary Guo]

On Wed Apr 1, 2026 at 12:45 PM BST, Miguel Ojeda wrote:
> From: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> 
> By default bindgen will convert 'enum lru_status' into a typedef for an
> integer. For the most part, an integer of the same size as the enum
> results in the correct ABI, but in the specific case of CFI, that is not
> the case. The CFI encoding is supposed to be the same as a struct called
> 'lru_status' rather than the name of the underlying native integer type.
> 
> To fix this, tell bindgen to generate a newtype and set the CFI type
> explicitly. Note that we need to set the CFI attribute explicitly as
> bindgen is using repr(transparent), which is otherwise identical to the
> inner type for ABI purposes.
> 
> This allows us to remove the page range helper C function in Binder
> without risking a CFI failure when list_lru_walk calls the provided
> function pointer.
> 
> The --with-attribute-custom-enum argument requires bindgen v0.71 or
> greater.
> 
> [ In particular, the feature was added in 0.71.0 [1][2].
> 
>   In addition, `feature(cfi_encoding)` has been available since
>   Rust 1.71.0 [3].
> 
>   Link: https://github.com/rust-lang/rust-bindgen/issues/2520 [1]
>   Link: https://github.com/rust-lang/rust-bindgen/pull/2866 [2]
>   Link: https://github.com/rust-lang/rust/pull/105452 [3]
> 
>     - Miguel ]
> 
> My testing procedure was to add this to the android17-6.18 branch and
> verify that rust_shrink_free_page is successfully called without crash,
> and verify that it does in fact crash when the cfi_encoding is set to
> other values. Note that I couldn't test this on android16-6.12 as that
> branch uses a bindgen version that is too old.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Link: https://patch.msgid.link/20260223-cfi-lru-status-v2-1-89c6448a63a4@xxxxxxxxxx
> [ Rebased on top of the minimum Rust version bump series which provide
>   the required `bindgen` version. - Miguel ]
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

> ---
>  drivers/android/binder/Makefile            |  3 +--
>  drivers/android/binder/page_range.rs       |  6 +++---
>  drivers/android/binder/page_range_helper.c | 24 ----------------------
>  drivers/android/binder/page_range_helper.h | 15 --------------
>  rust/bindgen_parameters                    |  4 ++++
>  rust/bindings/bindings_helper.h            |  1 -
>  rust/bindings/lib.rs                       |  1 +
>  rust/uapi/lib.rs                           |  1 +
>  8 files changed, 10 insertions(+), 45 deletions(-)
>  delete mode 100644 drivers/android/binder/page_range_helper.c
>  delete mode 100644 drivers/android/binder/page_range_helper.h