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

Alice Ryhl
2025-11-17T16:12:10Z

On Mon, Nov 17, 2025 at 4:37 PM Tamir Duberstein <tamird@gmail.com> wrote:
>
> On Mon, Nov 17, 2025 at 9:51 AM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > On Mon, Nov 17, 2025 at 07:04:17PM +1100, Stephen Rothwell wrote:
> > > Hi all,
> > >
> > > After merging the rust tree, today's linux-next build (x86_64
> > > allmodconfig) failed like this:
> > >
> > > error[E0277]: `Chipset` doesn't implement `core::fmt::Display`
> > > --> drivers/gpu/nova-core/gpu.rs:233:13
> > > |
> > > 233 | self.chipset,
> > > | ^^^^^^^^^^^^ `Chipset` cannot be formatted with the default formatter
> > > |
> > > = help: the trait `core::fmt::Display` is not implemented for `Chipset`
> > > = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
> > > = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
> > >
> > > error[E0277]: `Revision` doesn't implement `core::fmt::Display`
> > > --> drivers/gpu/nova-core/gpu.rs:235:13
> > > |
> > > 235 | self.revision
> > > | ^^^^^^^^^^^^^ `Revision` cannot be formatted with the default formatter
> > > |
> > > = help: the trait `core::fmt::Display` is not implemented for `Revision`
> > > = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
> > > = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
> > >
> > > error[E0277]: the trait bound `MsgFunction: kernel::fmt::Display` is not satisfied
> > > --> drivers/gpu/nova-core/gsp/cmdq.rs:532:9
> > > |
> > > 532 | / dev_dbg!(
> > > 533 | | &self.dev,
> > > 534 | | "GSP RPC: send: seq# {}, function={}, length=0x{:x}\n",
> > > | | -- required by a bound introduced by this call
> > > 535 | | self.seq,
> > > 536 | | M::FUNCTION,
> > > 537 | | dst.header.length(),
> > > 538 | | );
> > > | |_________^ the trait `kernel::fmt::Display` is not implemented for `MsgFunction`
> > > |
> > > = help: the following other types implement trait `kernel::fmt::Display`:
> > > &T
> > > Arc<T>
> > > Arguments<'_>
> > > BStr
> > > Box<T, A>
> > > CStr
> > > Chipset
> > > Class
> > > and 22 others
> > > = note: required for `kernel::fmt::Adapter<&MsgFunction>` to implement `core::fmt::Display`
> > > note: required by a bound in `core::fmt::rt::Argument::<'_>::new_display`
> > > --> /usr/lib/rustlib/src/rust/library/core/src/fmt/rt.rs:113:27
> > > |
> > > 113 | pub fn new_display<T: Display>(x: &T) -> Argument<'_> {
> > > | ^^^^^^^ required by this bound in `Argument::<'_>::new_display`
> > > = note: this error originates in the macro `::core::format_args` which comes from the expansion of the macro `dev_dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
> > >
> > > error: aborting due to 3 previous errors
> > >
> > > For more information about this error, try `rustc --explain E0277`.
> > >
> > > Caused by commit
> > >
> > > c5cf01ba8dfe ("rust: support formatting of foreign types")
> > >
> > > (I think) interacting with commits
> > >
> > > 38b7cc448a5b ("gpu: nova-core: implement Display for Spec")
> > > 75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and handling")
> > >
> > > from the drm-rust tree.
> >
> > I applied a patch to drm-rust-next that makes this error go away.
> >
> > Alice
>
> Thanks for taking care of this!
>
> Alexandre: the correct thing to do going forward is never to use
> `core::fmt`; instead always use `kernel::fmt`.

Here's the fix I applied:
https://lore.kernel.org/all/20251117-nova-fmt-rust-v1-1-651ca28cd98f@google.com/

I had to use write_fmt(fmt!(...)) instead of the write!(...) macro.

Alice