[PATCH 1/2] nova-core: Add a library for bitfields in Rust structs

Alexandre Courbot
Thu, 04 Sep 2025 03:16:40 -0000

On Thu Sep 4, 2025 at 12:15 AM JST, Joel Fernandes wrote:
<snip>
>>> +use kernel::prelude::*;
>>> +
>>> +/// Macro for defining bitfield-packed structures in Rust.
>>> +/// The size of the underlying storage type is specified with
#[repr(TYPE)].
>>> +///
>>> +/// # Example (just for illustration)
>>> +/// ```rust
>>> +/// bitstruct! {
>>> +///     #[repr(u64)]
>>> +///     pub struct PageTableEntry {
>>> +///         0:0       present     as bool,
>>> +///         1:1       writable    as bool,
>>> +///         11:9      available   as u8,
>>> +///         51:12     pfn         as u64,
>>> +///         62:52     available2  as u16,
>>> +///         63:63     nx          as bool,
>>
>> A note on syntax: for nova-core, we may want to use the `H:L` notation,
>> as this is what OpenRM uses, but in the larger kernel we might want to
>> use inclusive ranges (`L..=H`) as it will look more natural in Rust
>> code (and is the notation the `bits` module already uses).
>
> Perhaps future add-on enhancement to have both syntax? I'd like to
initially
> keep H:L and stabilize the code first, what do you think?

Let's have the discussion with the other stakeholders (Daniel?). I think
in Nova we want to keep the `H:L` syntax, as it matches what the OpenRM
headers do (so Nova would have its own `register` macro that calls into
the common one, tweaking things as it needs). But in the kernel crate we
should use something intuitive for everyone.