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

[Benno Lossin]

On Mon Apr 14, 2025 at 4:05 PM CEST, Alice Ryhl wrote:
> On Sat, Apr 12, 2025 at 10:01:22AM +0000, Benno Lossin wrote:
>> 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.
>
> Transparent newtypes for all integers would be super inconvenient.

Yeah I noticed that too when trying... We often assign integer literals
to the ffi types.

---
Cheers,
Benno