Re: Build: arm rustgcc unknown argument '-mno-fdpic'

[Ben Wolsieffer <ben.wolsieffer@hefring.com>]

On Sat, Apr 19, 2025 at 12:30:01AM +0200, Miguel Ojeda wrote:
> Thanks a lot for the details!
> 
> To clarify, this is for GCC kernel builds: skipping the flag is done
> for libclang under GCC builds (because `bindgen` always uses libclang,
> and `bindgen` is used by Rust to understand C headers).
> 
> So GCC will get the flag for the C side of the kernel builds, but
> libclang will not get the flag because Clang doesn't recognize it.
> Thus, if Clang vs. GCC differ in how they compute the layout of some
> type, then we would have an issue "mixing" them.
> 
> As you can imagine, GCC kernel builds with Rust enabled are a hack due
> to that, and it would be ideal to get `bindgen` to somehow be able to
> understand C headers as GCC does:
> 
>     https://github.com/rust-lang/rust-bindgen/issues/1949

-mno-fdpic disables a GCC feature that we don't want for kernel builds.
clang does not support this feature, so it always behaves as though
-mno-fdpic is passed. Therefore, it should be fine to mix the two, at
least as far as FDPIC is concerned.

Ben