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 ...

Merge patch series "`syn` support"

This patch series introduces support for `syn` (and its dependencies):

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

Merge patch series "`syn` support"

This patch series introduces support for `syn` (and its dependencies):

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.

It is the most downloaded Rust crate (according to crates.io), and it
is also used by the Rust compiler itself. Having such support allows to
greatly simplify writing complex macros such as `pin-init`. We will use
it in the `macros` crate too.

Benno has already prepared the `pin-init` version based on this, and on
top of that, we will be able to simplify the `macros` crate too. I think
Jesung is working on updating the `TryFrom` and `Into` upcoming derive
macros to use `syn` too.

The series starts with a few preparation commits (two fixes were already
merged in mainline that were discovered by this series), then each crate
is added. Finally, support for using the new crates from our `macros`
crate is introduced.

This has been a long time coming, e.g. even before Rust for Linux was
merged into the Linux kernel, Gary and Benno have wanted to use `syn`.
The first iterations of this, from 2022 and 2023 (with `serde` too,
another popular crate), are at:

https://github.com/Rust-for-Linux/linux/pull/910
https://github.com/Rust-for-Linux/linux/pull/1007

After those, we considered picking these from the distributions where
possible. However, after discussing it, it is not really worth the
complexity: vendoring makes things less complex and is less fragile.

In particular, we avoid having to support and test several versions,
we avoid having to introduce Cargo just to properly fetch the right
versions from the registry, we can easily customize the crates if needed
(e.g. dropping the `unicode_idents` dependency like it is done in this
series) and we simplify the configuration of the build for users for
which the "default" paths/registries would not have worked.

Moreover, nowadays, the ~57k lines introduced are not that much compared
to years ago (it dwarfed the actual Rust kernel code). Moreover, back
then it wasn't clear the Rust experiment would be a success, so it would
have been a bit pointless/risky to add many lines for nothing. Our macro
needs were also smaller in the early days.

So, finally, in Kangrejos 2025 we discussed going with the original,
simpler approach. Thus here it is the result.

There should not be many updates needed for these, and even if there
are, they should not be too big, e.g. +7k -3k lines across the 3 crates
in the last year.

Note that `syn` does not have all the features enabled, since we do not
need them so far, but they can easily be enabled just adding them to the
list.

Link: https://patch.msgid.link/20251124151837.2184382-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

show more ...

rust: syn: add SPDX License Identifiers

Originally, when the Rust upstream `alloc` standard library crate was
vendored in commit 057b8d257107 ("rust: adapt `alloc` crate to the
kernel"), the SPDX Li

rust: syn: add SPDX License Identifiers

Originally, when the Rust upstream `alloc` standard library crate was
vendored in commit 057b8d257107 ("rust: adapt `alloc` crate to the
kernel"), the SPDX License Identifiers were added to every file so that
the license on those was clear.

Thus do the same for the `syn` crate.

This makes `scripts/spdxcheck.py` pass.

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-17-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: syn: import crate

This is a subset of the Rust `syn` crate, version 2.0.106 (released
2025-08-16), licensed under "Apache-2.0 OR MIT", from:

https://github.com/dtolnay/syn/raw/2.0.106/src

rust: syn: import crate

This is a subset of the Rust `syn` crate, version 2.0.106 (released
2025-08-16), licensed under "Apache-2.0 OR MIT", from:

https://github.com/dtolnay/syn/raw/2.0.106/src

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

For copyright details, please see:

https://github.com/dtolnay/syn/blob/2.0.106/README.md#license
https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-APACHE
https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

for path in $(cd rust/syn/ && find . -type f -name '*.rs'); do
curl --silent --show-error --location \
https://github.com/dtolnay/syn/raw/2.0.106/src/$path \
| diff --unified rust/syn/$path - && echo $path: OK
done

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-16-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

show more ...