Subject: Re: linux-next: build failure after merge of the modules tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 5 Dec 2025 09:58:35 +1100

Hi all,

On Wed, 5 Nov 2025 15:51:09 +1100 Stephen Rothwell <[email-masked]> wrote:
>
> On Tue, 4 Nov 2025 15:45:00 +1100 Stephen Rothwell <[email-masked]> wrote:
> >
> > After merging the modules tree, today's linux-next build (x86_64
> > allmodconfig) failed like this:
> > 
> > error[E0308]: mismatched types  
> >   --> rust/kernel/module_param.rs:75:47    
> >    |
> > 75 |         let new_value = T::try_from_param_arg(arg)?;
> >    |                         --------------------- ^^^ expected `&BStr`, found `&CStr`
> >    |                         |
> >    |                         arguments to this function are incorrect
> >    |
> >    = note: expected reference `&BStr`
> >               found reference `&ffi::CStr`
> > note: associated function defined here  
> >   --> rust/kernel/module_param.rs:32:8    
> >    |
> > 32 |     fn try_from_param_arg(arg: &BStr) -> Result<Self>;
> >    |        ^^^^^^^^^^^^^^^^^^
> > 
> > error: aborting due to 1 previous error
> > 
> > For more information about this error, try `rustc --explain E0308`.
> > 
> > Caused by commit
> > 
> >   0b08fc292842 ("rust: introduce module_param module")
> > 
> > This is some interaction with something later in linux-next - presumably
> > commit
> > 
> >   3b83f5d5e78a ("rust: replace `CStr` with `core::ffi::CStr`")
> > 
> > from the rust tree.
> > 
> > Hopefully someone can provide a resolution for me tomorrow.
> > 
> > I have used the modules tree from next-20251103 for today.  
> 
> I have used the modules tree as is and applied the below merge
> resolution patch (supplied by Andreas) to the merge of the rust tree.
> 
> From: Stephen Rothwell <[email-masked]>
> Date: Wed, 5 Nov 2025 14:52:29 +1100
> Subject: [PATCH] fix up for "rust: replace `CStr` with `core::ffi::CStr`"
> 
> interacting with commit
> 
>   0b08fc292842 ("rust: introduce module_param module")
> 
> from the modules tree.
> 
> Signed-off-by: Stephen Rothwell <[email-masked]>
> ---
>  rust/kernel/module_param.rs | 1 +
>  rust/macros/module.rs       | 4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/module_param.rs b/rust/kernel/module_param.rs
> index e7d5c930a467..6a8a7a875643 100644
> --- a/rust/kernel/module_param.rs
> +++ b/rust/kernel/module_param.rs
> @@ -70,6 +70,7 @@ pub trait ModuleParam: Sized + Copy {
>      // SAFETY: By function safety requirement, val is non-null, null-terminated
>      // and valid for reads for the duration of this function.
>      let arg = unsafe { CStr::from_char_ptr(val) };
> +    let arg: &BStr = arg.as_ref();
>  
>      crate::error::from_result(|| {
>          let new_value = T::try_from_param_arg(arg)?;
> diff --git a/rust/macros/module.rs b/rust/macros/module.rs
> index 1a22de73d512..f6a94712384f 100644
> --- a/rust/macros/module.rs
> +++ b/rust/macros/module.rs
> @@ -133,10 +133,10 @@ fn emit_params(&mut self, info: &ModuleInfo) {
>                          ::kernel::module_param::KernelParam::new(
>                              ::kernel::bindings::kernel_param {{
>                                  name: if ::core::cfg!(MODULE) {{
> -                                    ::kernel::c_str!(\"{param_name}\").as_bytes_with_nul()
> +                                    ::kernel::c_str!(\"{param_name}\").to_bytes_with_nul()
>                                  }} else {{
>                                      ::kernel::c_str!(\"{module_name}.{param_name}\")
> -                                        .as_bytes_with_nul()
> +                                        .to_bytes_with_nul()
>                                  }}.as_ptr(),
>                                  // SAFETY: `__this_module` is constructed by the kernel at load
>                                  // time and will not be freed until the module is unloaded.
> -- 
> 2.51.1

This now needs to be applied to the merge of the modules tree (as the
rust tree has been merged by Linus).

-- 
Cheers,
Stephen Rothwell