Re: [PATCH] rust: fix building firmware abstraction on 32bit arm

[Benno Lossin]

On Fri Apr 11, 2025 at 4:15 PM CEST, Miguel Ojeda wrote:
> On Fri, Apr 11, 2025 at 2:46 PM Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
>>
>> Ah I overlooked this, you should be using `kernel::ffi` (or
>> `crate::ffi`) instead of `core`. (for `c_char` it doesn't matter, but we
>> shouldn't be using `core::ffi`, since we have our own mappings).
>
> In 6.6, C `char` changed to unsigned, but `core::ffi::c_char` is
> signed (in x86_64 at least).
>
> We should just never use `core::ffi` (except in `rust/ffi.rs`, of
> course) -- I think we should just add the C types to the prelude
> (which we discussed in the past) so that it is easy to avoid the
> mistake (something like the patch attached as the end result, but
> tested and across a kernel cycle or two) and mention it in the Coding
> Guidelines. Thoughts?

Yeah sounds like a good idea.

> I tried to use Clippy's `disallowed-types` too:
>
>     disallowed-types = [
>         { path = "core::ffi::c_void", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_char", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_schar", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_uchar", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_short", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_ushort", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_int", reason = "the `kernel::ffi` types
> should be used instead" },
>         { path = "core::ffi::c_uint", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_long", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_ulong", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_longlong", reason = "the `kernel::ffi`
> types should be used instead" },
>         { path = "core::ffi::c_ulonglong", reason = "the `kernel::ffi`
> types should be used instead" },
>     ]
>
> But it goes across aliases.

We could make the types in `ffi` be transparent newtypes. But not sure
if that could interfere with kCFI or other stuff.

---
Cheers,
Benno