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Add a macro to denote this explicitly. This is similar to C++'s consteval keyword. Convert device_id.rs as an example. Signed-off-by: Gary Guo --- rust/build_error.rs | 7 +++++++ rust/kernel/const_eval.rs | 9 +++++++++ rust/kernel/device_id.rs | 4 ++++ rust/kernel/lib.rs | 1 + rust/macros/const_eval.rs | 24 ++++++++++++++++++++++++ rust/macros/lib.rs | 21 +++++++++++++++++++++ 6 files changed, 66 insertions(+) diff --git a/rust/build_error.rs b/rust/build_error.rs index fa24eeef9929..b7ef80596f1f 100644 --- a/rust/build_error.rs +++ b/rust/build_error.rs @@ -29,3 +29,10 @@ pub const fn build_error(msg: &'static str) -> ! { panic!("{}", msg); } + +/// Assert that the code is in const evaluation. +/// +/// Triggers a build error if called at runtime. +#[inline(never)] +#[export_name = "rust_const_eval_called_at_runtime"] +pub const fn assert_in_const_eval() {} diff --git a/rust/kernel/const_eval.rs b/rust/kernel/const_eval.rs new file mode 100644 index 000000000000..f1b79d82549d --- /dev/null +++ b/rust/kernel/const_eval.rs @@ -0,0 +1,9 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Utilities for const evaluation. + +#[doc(inline)] +pub use build_error::assert_in_const_eval; + +#[doc(inline)] +pub use macros::const_eval_only; diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs index c81fca5b4986..dad9cadaeb1b 100644 --- a/rust/kernel/device_id.rs +++ b/rust/kernel/device_id.rs @@ -10,6 +10,8 @@ mem::MaybeUninit, // }; +use crate::const_eval::const_eval_only; + /// Marker trait to indicate a Rust device ID type represents a corresponding C device ID type. /// /// This is meant to be implemented by buses/subsystems so that they can use [`IdTable`] to @@ -108,6 +110,7 @@ impl IdArray Self { let mut raw_ids = [const { MaybeUninit::::uninit() }; N]; @@ -144,6 +147,7 @@ impl IdArray { /// /// The contents are derived from the given identifiers and context information. /// If the device implements [`RawDeviceIdIndex`], consider using [`IdArray::new`] instead. + #[const_eval_only] pub const fn new_without_index(ids: [T; N]) -> Self { // SAFETY: `T` is layout-wise compatible with `T::RawType`, so is the array of them. let raw_ids: [MaybeUninit; N] = unsafe { core::mem::transmute_copy(&ids) }; diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 4d5c96ddc49c..d9ed25e96ff3 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -57,6 +57,7 @@ pub mod clk; #[cfg(CONFIG_CONFIGFS_FS)] pub mod configfs; +pub mod const_eval; pub mod cpu; #[cfg(CONFIG_CPU_FREQ)] pub mod cpufreq; diff --git a/rust/macros/const_eval.rs b/rust/macros/const_eval.rs new file mode 100644 index 000000000000..0664888d3b38 --- /dev/null +++ b/rust/macros/const_eval.rs @@ -0,0 +1,24 @@ +// SPDX-License-Identifier: GPL-2.0 + +use proc_macro2::TokenStream; +use quote::ToTokens; +use syn::{ + parse_quote, + ItemFn, // +}; + +pub(crate) fn const_eval_only(mut input: ItemFn) -> TokenStream { + // Prevent code generation as the function is for const evaluation only. + input.attrs.push(parse_quote!( + #[inline(always)] + )); + + input.block.stmts.insert( + 0, + parse_quote!( + ::kernel::const_eval::assert_in_const_eval(); + ), + ); + + input.into_token_stream() +} diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs index 24f96feaeb34..e47a8c35ccff 100644 --- a/rust/macros/lib.rs +++ b/rust/macros/lib.rs @@ -15,6 +15,7 @@ #![cfg_attr(not(CONFIG_RUSTC_HAS_SPAN_FILE), feature(proc_macro_span))] mod concat_idents; +mod const_eval; mod export; mod fmt; mod for_lt; @@ -338,6 +339,26 @@ pub fn concat_idents(input: TokenStream) -> TokenStream { concat_idents::concat_idents(parse_macro_input!(input)).into() } +/// Mark a function as usable from const evaluation only. +/// +/// Build will fail if the function is used for runtime code. +/// +/// # Examples +/// +/// ``` +/// #[const_eval_only] +/// const fn call_for_const_eval_only() { +/// // This code will be executed only during const eval! +/// } +/// +/// const _: () = call_for_const_eval_only(); +/// ``` +#[proc_macro_attribute] +pub fn const_eval_only(attr: TokenStream, input: TokenStream) -> TokenStream { + parse_macro_input!(attr as syn::parse::Nothing); + const_eval::const_eval_only(parse_macro_input!(input)).into() +} + /// Paste identifiers together. /// /// Within the `paste!` macro, identifiers inside `[<` and `>]` are concatenated together to form a -- 2.54.0