linux-kernel - Re: [PATCH v2] rust: Use `ffi::c_char` type in firmware abstraction `FwFunc`

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Message-ID: <Z_p-UoycGk3BceXm@pollux>
Date: Sat, 12 Apr 2025 16:53:06 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Christian Schrefl <chrisi.schrefl@...il.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
	Russ Weight <russ.weight@...ux.dev>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2] rust: Use `ffi::c_char` type in firmware abstraction
 `FwFunc`

On Sat, Apr 12, 2025 at 12:29:48PM +0200, Christian Schrefl wrote:
> The `FwFunc` struct contains an function with a char pointer argument,
> for which a `*const u8` pointer was used. This is not really the
> "propper" type for this, so use a `*const kernel::ffi::c_char` pointer
> instad.
> 
> This has no real functionality changes, since `kernel::ffi::c_char` is
> a type alias to `u8` anyways.
> 
> This used to cause problems on 6.13 when building for 32 bit arm (with
> my patches), since rust mapped c_char to i8 instead.

Now that I read this again:

Isn't it the other way around? For arm32 c_char was mapped to u8, but FwFunc
expected i8 (since that's what c_char was mapped to for all other architectures
that are supported in v6.13).

Can you please clarify this in the commit message?