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

Daniel Almeida
Thu, 04 Sep 2025 11:02:16 -0000

> On 4 Sep 2025, at 00:16, Alexandre Courbot <acourbot at nvidia.com>
wrote:
>
> 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.
>

I don?t specifically care which syntax is used. We will adapt to it.

? Daniel