Re: [PATCH v2] rust: bug: fix warn_on macro build error on UML

On Fri, Aug 7, 2026 at 1:24 PM FUJITA Tomonori <[email protected]> wrote:
>
> From: FUJITA Tomonori <[email protected]>
>
> Callers that go through `kernel::prelude` have `CStrExt` in scope, but
> code inside the `kernel` crate imports explicitly and may not. Using
> `warn_on!` from such a module fails to build on UML, which is the only
> configuration where `warn_flags!` needs a C string pointer rather than an
> inline asm bug entry:
>
> error[E0599]: no method named `as_char_ptr` found for reference `&ffi::CStr` in the current scope
>    --> linux/rust/kernel/bug.rs:83:49
>     |
>  83 |                 $crate::c_str!(::core::file!()).as_char_ptr(),
>     |                                                 ^^^^^^^^^^^
>     |
>    ::: linux/rust/kernel/time.rs:427:9
>     |
> 427 |         warn_on!(self.nanos < 0);
>     |         ------------------------ in this macro invocation
>     |
>     = help: items from traits can only be used if the trait is in scope
>     = note: this error originates in the macro `$crate::warn_flags` which comes from the expansion of the macro `warn_on` (in Nightly builds, run with -Z mac)
> help: trait `CStrExt` which provides `as_char_ptr` is implemented but not in scope; perhaps you want to import it
>    --> linux/rust/kernel/time.rs:27:1
>     |
>  27 + use crate::str::CStrExt;
>
> Call the method through its fully qualified path, which resolves
> without any import at the expansion site.
>
> Cc: [email protected]
> Fixes: dff64b072708 ("rust: Add warn_on macro")
> Signed-off-by: FUJITA Tomonori <[email protected]>

Applied to `rust-next` -- thanks!

Cheers,
Miguel