Hi!
The Rust firmware abstractions FTBFS on arm64 and current stable
(6.13.4) when compiled with rustc 1.85.0:
```
RUSTC L rust/kernel.o
error[E0308]: mismatched types
--> rust/kernel/firmware.rs:20:14
|
20 | Self(bindings::request_firmware)
| ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found
fn item
| |
| arguments to this function are incorrect
|
= note: expected fn pointer `unsafe extern "C" fn(_, *const i8, _) -> _`
found fn item `unsafe extern "C" fn(_, *const u8, _)
-> _ {request_firmware}`
note: tuple struct defined here
--> rust/kernel/firmware.rs:14:8
|
14 | struct FwFunc(
| ^^^^^^
error[E0308]: mismatched types
--> rust/kernel/firmware.rs:24:14
|
24 | Self(bindings::firmware_request_nowarn)
| ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected fn
pointer, found fn item
| |
| arguments to this function are incorrect
|
= note: expected fn pointer `unsafe extern "C" fn(_, *const i8, _) -> _`
found fn item `unsafe extern "C" fn(_, *const u8, _)
-> _ {firmware_request_nowarn}`
note: tuple struct defined here
--> rust/kernel/firmware.rs:14:8
|
14 | struct FwFunc(
| ^^^^^^
error[E0308]: mismatched types
--> rust/kernel/firmware.rs:64:45
|
64 | let ret = unsafe { func.0(pfw as _, name.as_char_ptr(),
dev.as_raw()) };
| ------ ^^^^^^^^^^^^^^^^^^
expected `*const i8`, found `*const u8`
| |
| arguments to this function are incorrect
|
= note: expected raw pointer `*const i8`
found raw pointer `*const u8`
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0308`.
```
This is because rustc 1.85 (now stable) switched core::ffi::c_char from
i8 to u8 on arm64 and other platforms [1], and because current stable
still uses rustc's core's instead of the custom ffi integer types like
6.14 will. Looking for other i8's in *.rs files tells me only the QR
code panic screen should be affected in addition to the firmware
abstractions, and that was already reported in [2].
A simple fix would be to switch i8 to u8 in `struct FwFunc`, but that
breaks rustc <= 1.84 so I guess a more robust solution is needed.
Cheers!
[1] https://github.com/rust-lang/rust/pull/132975
[2]
https://lore.kernel.org/all/20250120124531.2581448-1-linkmauve@xxxxxxxxxxxx/
