it seems c_char is set to u8, not i8

[sprhawk]

my target is aarch64 (Raspberry Pi 4) host is Debian Buster x86_64.

I'm using poky dunfell branch, use HEAD revision of meta-rust-bin.

My Rust project using bindgen to generate ffi wrapping. it can be build successfully in normal x86_64 environment.

But using yocto + meta-rust-bin + meta-clang(for bindgen), the build failed.

for following reason:

| ffi::receive(*self.client.borrow(), pointer.cast::<i8>(), length, &mut read_length)
|     |                                                                           ^^^^^^^^^^^^^^^^^^^^ expected `u8`, found `i8`

the generated binding for receive is:

receive ( client :client_t , data : * mut :: std :: os :: raw :: c_char , length : u32 , bytes : * mut u32 )

it seems all required c_char is "expected u8"

i saw these issues rust-lang/rust-bindgen#559, rust-lang/rust-bindgen#603, it may be related clang? or rust std?

Should I replace parameters to ffi binding from i8/u8 to just c_char instead?