Re: [PATCH] drm/panic: fix compilation issue on ARM

[Alice Ryhl <alice@ryhl.io>]

On 1/20/25 10:52 PM, Miguel Ojeda wrote:
> Hi Emmanuel,
> 
> On Mon, Jan 20, 2025 at 1:45 PM Emmanuel Gil Peyrot
> <linkmauve@linkmauve.fr> wrote:
>>
>> In C, the char type is specified with “The implementation shall define char to
>> have the same range, representation, and behavior as either signed char or
>> unsigned char.”
>>
>> On x86 it defaults to signed char, and on ARM it defaults to unsigned char.
>> This carries over to Rust’s FFI, which aliases its c_char type to i8 on x86,
>> and to u8 on ARM.
> 
> In the kernel `-funsigned-char` is used, see commit 3bc753c06dd0
> ("kbuild: treat char as always unsigned").
> 
> In any case, the change is fine, because we want to use the proper
> type, but this is already in the Rust PR for this cycle, which should
> land in mainline in some days, see commit 27c7518e7f1c ("rust: finish
> using custom FFI integer types") in rust-next.
> 
> However, I am nevertheless confused, because in mainline
> `crate::ffi::c_char` is `core::ffi::c_char` which is `i8` in both
> arm64 and x86_64 and thus there is no build issue there.
Isn't core::ffi::c_char an u8 on arm64?

Alice