Merge tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:

- Add support for 'syn'.

Syn is a pa

Merge tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:

- Add support for 'syn'.

Syn is a parsing library for parsing a stream of Rust tokens into a
syntax tree of Rust source code.

Currently this library is geared toward use in Rust procedural
macros, but contains some APIs that may be useful more generally.

'syn' allows us to greatly simplify writing complex macros such as
'pin-init' (Benno has already prepared the 'syn'-based version). We
will use it in the 'macros' crate too.

'syn' is the most downloaded Rust crate (according to crates.io),
and it is also used by the Rust compiler itself. While the amount
of code is substantial, there should not be many updates needed for
these crates, and even if there are, they should not be too big,
e.g. +7k -3k lines across the 3 crates in the last year.

'syn' requires two smaller dependencies: 'quote' and 'proc-macro2'.
I only modified their code to remove a third dependency
('unicode-ident') and to add the SPDX identifiers. The code can be
easily verified to exactly match upstream with the provided
scripts.

They are all licensed under "Apache-2.0 OR MIT", like the other
vendored 'alloc' crate we had for a while.

Please see the merge commit with the cover letter for more context.

- Allow 'unreachable_pub' and 'clippy::disallowed_names' for
doctests.

Examples (i.e. doctests) may want to do things like show public
items and use names such as 'foo'.

Nevertheless, we still try to keep examples as close to real code
as possible (this is part of why running Clippy on doctests is
important for us, e.g. for safety comments, which userspace Rust
does not support yet but we are stricter).

'kernel' crate:

- Replace our custom 'CStr' type with 'core::ffi::CStr'.

Using the standard library type reduces our custom code footprint,
and we retain needed custom functionality through an extension
trait and a new 'fmt!' macro which replaces the previous 'core'
import.

This started in 6.17 and continued in 6.18, and we finally land the
replacement now. This required quite some stamina from Tamir, who
split the changes in steps to prepare for the flag day change here.

- Replace 'kernel::c_str!' with C string literals.

C string literals were added in Rust 1.77, which produce '&CStr's
(the 'core' one), so now we can write:

c"hi"

instead of:

c_str!("hi")

- Add 'num' module for numerical features.

It includes the 'Integer' trait, implemented for all primitive
integer types.

It also includes the 'Bounded' integer wrapping type: an integer
value that requires only the 'N' least significant bits of the
wrapped type to be encoded:

// An unsigned 8-bit integer, of which only the 4 LSBs are used.
let v = Bounded::<u8, 4>::new::<15>();
assert_eq!(v.get(), 15);

'Bounded' is useful to e.g. enforce guarantees when working with
bitfields that have an arbitrary number of bits.

Values can also be constructed from simple non-constant expressions
or, for more complex ones, validated at runtime.

'Bounded' also comes with comparison and arithmetic operations
(with both their backing type and other 'Bounded's with a
compatible backing type), casts to change the backing type,
extending/shrinking and infallible/fallible conversions from/to
primitives as applicable.

- 'rbtree' module: add immutable cursor ('Cursor').

It enables to use just an immutable tree reference where
appropriate. The existing fully-featured mutable cursor is renamed
to 'CursorMut'.

kallsyms:

- Fix wrong "big" kernel symbol type read from procfs.

'pin-init' crate:

- A couple minor fixes (Benno asked me to pick these patches up for
him this cycle).

Documentation:

- Quick Start guide: add Debian 13 (Trixie).

Debian Stable is now able to build Linux, since Debian 13 (released
2025-08-09) packages Rust 1.85.0, which is recent enough.

We are planning to propose that the minimum supported Rust version
in Linux follows Debian Stable releases, with Debian 13 being the
first one we upgrade to, i.e. Rust 1.85.

MAINTAINERS:

- Add entry for the new 'num' module.

- Remove Alex as Rust maintainer: he hasn't had the time to
contribute for a few years now, so it is a no-op change in
practice.

And a few other cleanups and improvements"

* tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: (53 commits)
rust: macros: support `proc-macro2`, `quote` and `syn`
rust: syn: enable support in kbuild
rust: syn: add `README.md`
rust: syn: remove `unicode-ident` dependency
rust: syn: add SPDX License Identifiers
rust: syn: import crate
rust: quote: enable support in kbuild
rust: quote: add `README.md`
rust: quote: add SPDX License Identifiers
rust: quote: import crate
rust: proc-macro2: enable support in kbuild
rust: proc-macro2: add `README.md`
rust: proc-macro2: remove `unicode_ident` dependency
rust: proc-macro2: add SPDX License Identifiers
rust: proc-macro2: import crate
rust: kbuild: support using libraries in `rustc_procmacro`
rust: kbuild: support skipping flags in `rustc_test_library`
rust: kbuild: add proc macro library support
rust: kbuild: simplify `--cfg` handling
rust: kbuild: introduce `core-flags` and `core-skip_flags`
...

show more ...

rust: num: bounded: rename `try_into_bitint` to `try_into_bounded`

This is a remnant from when `Bounded` was called `BitInt` which I didn't
rename. Fix this.

Fixes: 01e345e82ec3 ("rust: num: add Bo

rust: num: bounded: rename `try_into_bitint` to `try_into_bounded`

This is a remnant from when `Bounded` was called `BitInt` which I didn't
rename. Fix this.

Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20251124-bounded_fix-v1-1-d8e34e1c727f@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

show more ...

rust: num: bounded: Always inline fits_within and from_expr

`from_expr` relies on `build_assert` to infer that the passed expression
fits the type's boundaries at build time. That inference can only

rust: num: bounded: Always inline fits_within and from_expr

`from_expr` relies on `build_assert` to infer that the passed expression
fits the type's boundaries at build time. That inference can only be
successful its code (and that of `fits_within`, which performs the
check) is inlined, as a dedicated function would need to work with a
variable and cannot verify that property.

While inlining happens as expected in most cases, it is not guaranteed.
In particular, kernel options that optimize for size like
`CONFIG_CC_OPTIMIZE_FOR_SIZE` can result in `from_expr` not being
inlined.

Add `#[inline(always)]` attributes to both `fits_within` and `from_expr`
to make the compiler inline these functions more aggressively, as it
does not make sense to use them non-inlined anyway.

[ For reference, the errors look like:

ld.lld: error: undefined symbol: rust_build_error
>>> referenced by build_assert.rs:83 (rust/kernel/build_assert.rs:83)
>>> rust/doctests_kernel_generated.o:(<kernel::num::bounded::Bounded<u8, 1>>::from_expr) in archive vmlinux.a

- Miguel ]

Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511210055.RUsFNku1-lkp@intel.com/
Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20251122-bounded_ints_fix-v1-1-1e07589d4955@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

show more ...

rust: num: add Bounded integer wrapping type

Add the `Bounded` integer wrapper type, which restricts the number of
bits allowed to represent of value.

This is useful to e.g. enforce guarantees when

rust: num: add Bounded integer wrapping type

Add the `Bounded` integer wrapper type, which restricts the number of
bits allowed to represent of value.

This is useful to e.g. enforce guarantees when working with bitfields
that have an arbitrary number of bits.

Alongside this type, provide many `From` and `TryFrom` implementations
are to reduce friction when using with regular integer types. Proxy
implementations of common integer operations are also provided.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251108-bounded_ints-v4-2-c9342ac7ebd1@nvidia.com
[ Added intra-doc link. Fixed a few other nits. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

show more ...