Commit ec87ec35 authored by Benno Lossin's avatar Benno Lossin
Browse files

rust: pin-init: implement `ZeroableOption` for function pointers with up to 20 arguments 

`Option<[unsafe] [extern "abi"] fn(...args...) -> ret>` is documented
[1] to also have the `None` variant equal all zeroes.

Link: https://doc.rust-lang.org/stable/std/option/index.html#representation [1]
Link: https://github.com/Rust-for-Linux/pin-init/pull/56/commits/b6c1ab4fb3699765f81ae512ecac5a2f032d8d51
Link: https://lore.kernel.org/all/20250523145125.523275-7-lossin@kernel.org


Signed-off-by: default avatarBenno Lossin <lossin@kernel.org>
parent 9f473538

rust/pin-init/src/lib.rs

+16 −0
Original line number Diff line number Diff line
@@ -1662,6 +1662,22 @@ unsafe impl<$first: Zeroable, $($t: Zeroable),*> Zeroable for ($first, $($t),*) 


impl_tuple_zeroable!(A, B, C, D, E, F, G, H, I, J);



macro_rules! impl_fn_zeroable_option {

    ([$($abi:literal),* $(,)?] $args:tt) => {

        $(impl_fn_zeroable_option!({extern $abi} $args);)*

        $(impl_fn_zeroable_option!({unsafe extern $abi} $args);)*

    };

    ({$($prefix:tt)*} {$(,)?}) => {};

    ({$($prefix:tt)*} {$ret:ident, $($rest:ident),* $(,)?}) => {

        // SAFETY: function pointers are part of the option layout optimization:

        // <https://doc.rust-lang.org/stable/std/option/index.html#representation>.

        unsafe impl<$ret, $($rest),*> ZeroableOption for $($prefix)* fn($($rest),*) -> $ret {}

        impl_fn_zeroable_option!({$($prefix)*} {$($rest),*,});

    };

}



impl_fn_zeroable_option!(["Rust", "C"] { A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U });



/// This trait allows creating an instance of `Self` which contains exactly one

/// [structurally pinned value](https://doc.rust-lang.org/std/pin/index.html#projections-and-structural-pinning).

///