[PATCH v2 00/27] Allow inlining C helpers into Rust when using LTO

[PATCH v2 00/27] Allow inlining C helpers into Rust when using LTO

[Alice Ryhl]

This patch series adds __rust_helper to every single rust helper. The
patches do not depend on each other, so maintainers please go ahead and
pick up any patches relevant to your subsystem! Or provide your Acked-by
so that Miguel can pick them up.

These changes were generated by adding __rust_helper and running
ClangFormat. Unrelated formatting changes were removed manually.

Why is __rust_helper needed?
============================

Currently, C helpers cannot be inlined into Rust even when using LTO
because LLVM detects slightly different options on the codegen units.

* LLVM doesn't want to inline functions compiled with
  `-fno-delete-null-pointer-checks` with code compiled without. The C
  CGUs all have this enabled and Rust CGUs don't. Inlining is okay since
  this is one of the hardening features that does not change the ABI,
  and we shouldn't have null pointer dereferences in these helpers.

* LLVM doesn't want to inline functions with different list of builtins. C
  side has `-fno-builtin-wcslen`; `wcslen` is not a Rust builtin, so
  they should be compatible, but LLVM does not perform inlining due to
  attributes mismatch.

* clang and Rust doesn't have the exact target string. Clang generates
  `+cmov,+cx8,+fxsr` but Rust doesn't enable them (in fact, Rust will
  complain if `-Ctarget-feature=+cmov,+cx8,+fxsr` is used). x86-64
  always enable these features, so they are in fact the same target
  string, but LLVM doesn't understand this and so inlining is inhibited.
  This can be bypassed with `--ignore-tti-inline-compatible`, but this
  is a hidden option.

(This analysis was written by Gary Guo.)

How is this fixed?
==================

To fix this we need to add __always_inline to all helpers when compiling
with LTO. However, it should not be added when running bindgen as
bindgen will ignore functions marked inline. To achieve this, we are
using a #define called __rust_helper that is defined differently
depending on whether bindgen is running or not.

Note that __rust_helper is currently always #defined to nothing.
Changing it to __always_inline will happen separately in another patch
series.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Changes in v2:
- Pick up Reviewed-by: Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>
- Update formatting in mm and slab patches.
- Add new helpers in files uaccess, pwm, and time.
- Drop any patches that have been merged.
- Link to v1: https://lore.kernel.org/r/20251202-define-rust-helper-v1-0-a2e13cbc17a6@google.com

---
Alice Ryhl (27):
      rust: barrier: add __rust_helper to helpers
      rust: blk: add __rust_helper to helpers
      rust: bug: add __rust_helper to helpers
      rust: clk: add __rust_helper to helpers
      rust: completion: add __rust_helper to helpers
      rust: cpu: add __rust_helper to helpers
      rust: cred: add __rust_helper to helpers
      rust: err: add __rust_helper to helpers
      rust: jump_label: add __rust_helper to helpers
      rust: maple_tree: add __rust_helper to helpers
      rust: mm: add __rust_helper to helpers
      rust: of: add __rust_helper to helpers
      rust: processor: add __rust_helper to helpers
      rust: pwm: add __rust_helper to helpers
      rust: rbtree: add __rust_helper to helpers
      rust: rcu: add __rust_helper to helpers
      rust: refcount: add __rust_helper to helpers
      rust: security: add __rust_helper to helpers
      rust: slab: add __rust_helper to helpers
      rust: sync: add __rust_helper to helpers
      rust: task: add __rust_helper to helpers
      rust: time: add __rust_helper to helpers
      rust: uaccess: add __rust_helper to helpers
      rust: usb: add __rust_helper to helpers
      rust: wait: add __rust_helper to helpers
      rust: workqueue: add __rust_helper to helpers
      rust: xarray: add __rust_helper to helpers

 rust/helpers/barrier.c    |  6 +++---
 rust/helpers/blk.c        |  4 ++--
 rust/helpers/bug.c        |  4 ++--
 rust/helpers/build_bug.c  |  2 +-
 rust/helpers/clk.c        | 24 +++++++++++++-----------
 rust/helpers/completion.c |  2 +-
 rust/helpers/cpu.c        |  2 +-
 rust/helpers/cred.c       |  4 ++--
 rust/helpers/err.c        |  6 +++---
 rust/helpers/jump_label.c |  2 +-
 rust/helpers/maple_tree.c |  3 ++-
 rust/helpers/mm.c         | 20 ++++++++++----------
 rust/helpers/mutex.c      | 13 +++++++------
 rust/helpers/of.c         |  2 +-
 rust/helpers/page.c       |  9 +++++----
 rust/helpers/processor.c  |  2 +-
 rust/helpers/pwm.c        |  6 +++---
 rust/helpers/rbtree.c     |  9 +++++----
 rust/helpers/rcu.c        |  4 ++--
 rust/helpers/refcount.c   | 10 +++++-----
 rust/helpers/security.c   | 26 +++++++++++++++-----------
 rust/helpers/signal.c     |  2 +-
 rust/helpers/slab.c       |  4 ++--
 rust/helpers/spinlock.c   | 13 +++++++------
 rust/helpers/sync.c       |  4 ++--
 rust/helpers/task.c       | 24 ++++++++++++------------
 rust/helpers/time.c       | 14 +++++++-------
 rust/helpers/uaccess.c    | 10 ++++++----
 rust/helpers/usb.c        |  3 ++-
 rust/helpers/vmalloc.c    |  2 +-
 rust/helpers/wait.c       |  2 +-
 rust/helpers/workqueue.c  |  8 +++++---
 rust/helpers/xarray.c     | 10 +++++-----
 33 files changed, 136 insertions(+), 120 deletions(-)
---
base-commit: 9ace4753a5202b02191d54e9fdf7f9e3d02b85eb
change-id: 20251202-define-rust-helper-f7b531813007

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>

[PATCH v2 07/27] rust: cred: add __rust_helper to helpers

[Alice Ryhl]

This is needed to inline these helpers into Rust code.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge Hallyn <sergeh@kernel.org>
Cc: linux-security-module@vger.kernel.org
---
 rust/helpers/cred.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/helpers/cred.c b/rust/helpers/cred.c
index fde7ae20cdd19f04ac5f28808586c65de6b72f09..a56a7b7536232733dcdc640f09f8f2537e69d75e 100644
--- a/rust/helpers/cred.c
+++ b/rust/helpers/cred.c
@@ -2,12 +2,12 @@
 
 #include <linux/cred.h>
 
-const struct cred *rust_helper_get_cred(const struct cred *cred)
+__rust_helper const struct cred *rust_helper_get_cred(const struct cred *cred)
 {
 	return get_cred(cred);
 }
 
-void rust_helper_put_cred(const struct cred *cred)
+__rust_helper void rust_helper_put_cred(const struct cred *cred)
 {
 	put_cred(cred);
 }

-- 
2.52.0.351.gbe84eed79e-goog

[PATCH v2 18/27] rust: security: add __rust_helper to helpers

[Alice Ryhl]

This is needed to inline these helpers into Rust code.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Cc: Paul Moore <paul@paul-moore.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-security-module@vger.kernel.org
---
 rust/helpers/security.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/rust/helpers/security.c b/rust/helpers/security.c
index ca22da09548dfed95a83168ed09263e75cf08fd2..8d0a25fcf931ac6540a986aa10187c345614fc9e 100644
--- a/rust/helpers/security.c
+++ b/rust/helpers/security.c
@@ -3,41 +3,45 @@
 #include <linux/security.h>
 
 #ifndef CONFIG_SECURITY
-void rust_helper_security_cred_getsecid(const struct cred *c, u32 *secid)
+__rust_helper void rust_helper_security_cred_getsecid(const struct cred *c,
+						      u32 *secid)
 {
 	security_cred_getsecid(c, secid);
 }
 
-int rust_helper_security_secid_to_secctx(u32 secid, struct lsm_context *cp)
+__rust_helper int rust_helper_security_secid_to_secctx(u32 secid,
+						       struct lsm_context *cp)
 {
 	return security_secid_to_secctx(secid, cp);
 }
 
-void rust_helper_security_release_secctx(struct lsm_context *cp)
+__rust_helper void rust_helper_security_release_secctx(struct lsm_context *cp)
 {
 	security_release_secctx(cp);
 }
 
-int rust_helper_security_binder_set_context_mgr(const struct cred *mgr)
+__rust_helper int
+rust_helper_security_binder_set_context_mgr(const struct cred *mgr)
 {
 	return security_binder_set_context_mgr(mgr);
 }
 
-int rust_helper_security_binder_transaction(const struct cred *from,
-					    const struct cred *to)
+__rust_helper int
+rust_helper_security_binder_transaction(const struct cred *from,
+					const struct cred *to)
 {
 	return security_binder_transaction(from, to);
 }
 
-int rust_helper_security_binder_transfer_binder(const struct cred *from,
-						const struct cred *to)
+__rust_helper int
+rust_helper_security_binder_transfer_binder(const struct cred *from,
+					    const struct cred *to)
 {
 	return security_binder_transfer_binder(from, to);
 }
 
-int rust_helper_security_binder_transfer_file(const struct cred *from,
-					      const struct cred *to,
-					      const struct file *file)
+__rust_helper int rust_helper_security_binder_transfer_file(
+	const struct cred *from, const struct cred *to, const struct file *file)
 {
 	return security_binder_transfer_file(from, to, file);
 }

-- 
2.52.0.351.gbe84eed79e-goog

Re: [PATCH v2 00/27] Allow inlining C helpers into Rust when using LTO

[Boqun Feng]

On Mon, Jan 05, 2026 at 12:42:13PM +0000, Alice Ryhl wrote:
> This patch series adds __rust_helper to every single rust helper. The
> patches do not depend on each other, so maintainers please go ahead and
> pick up any patches relevant to your subsystem! Or provide your Acked-by
> so that Miguel can pick them up.
> 

I queued the following into rust-sync:

       rust: barrier: add __rust_helper to helpers
       rust: blk: add __rust_helper to helpers
       rust: completion: add __rust_helper to helpers
       rust: cpu: add __rust_helper to helpers
       rust: processor: add __rust_helper to helpers
       rust: rcu: add __rust_helper to helpers
       rust: refcount: add __rust_helper to helpers
       rust: sync: add __rust_helper to helpers
       rust: task: add __rust_helper to helpers
       rust: time: add __rust_helper to helpers
       rust: wait: add __rust_helper to helpers

Thanks!

Regards,
Boqun

> These changes were generated by adding __rust_helper and running
> ClangFormat. Unrelated formatting changes were removed manually.
> 
[...]

Re: [PATCH v2 07/27] rust: cred: add __rust_helper to helpers

[Paul Moore]

On Mon, Jan 5, 2026 at 7:42 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> This is needed to inline these helpers into Rust code.
>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Cc: Paul Moore <paul@paul-moore.com>
> Cc: Serge Hallyn <sergeh@kernel.org>
> Cc: linux-security-module@vger.kernel.org
> ---
>  rust/helpers/cred.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Acked-by: Paul Moore <paul@paul-moore.com>

-- 
paul-moore.com

Re: [PATCH v2 07/27] rust: cred: add __rust_helper to helpers

[Paul Moore]

On Tue, Jan 6, 2026 at 8:25 PM Paul Moore <paul@paul-moore.com> wrote:
>
> On Mon, Jan 5, 2026 at 7:42 AM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > This is needed to inline these helpers into Rust code.
> >
> > Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> > Reviewed-by: Gary Guo <gary@garyguo.net>
> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> > ---
> > Cc: Paul Moore <paul@paul-moore.com>
> > Cc: Serge Hallyn <sergeh@kernel.org>
> > Cc: linux-security-module@vger.kernel.org
> > ---
> >  rust/helpers/cred.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
>
> Acked-by: Paul Moore <paul@paul-moore.com>

Ooops, sorry, I just saw that these were okay to merge into the
various subsystem trees.  Merged into lsm/dev, thanks.

-- 
paul-moore.com

Re: [PATCH v2 18/27] rust: security: add __rust_helper to helpers

[Paul Moore]

On Mon, Jan 5, 2026 at 7:43 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> This is needed to inline these helpers into Rust code.
>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Cc: Paul Moore <paul@paul-moore.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: linux-security-module@vger.kernel.org
> ---
>  rust/helpers/security.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)

Merged into lsm/dev, thanks.

-- 
paul-moore.com

Re: [PATCH v2 07/27] rust: cred: add __rust_helper to helpers

[Alice Ryhl]

On Wed, Jan 7, 2026 at 2:29 AM Paul Moore <paul@paul-moore.com> wrote:
>
> On Tue, Jan 6, 2026 at 8:25 PM Paul Moore <paul@paul-moore.com> wrote:
> >
> > On Mon, Jan 5, 2026 at 7:42 AM Alice Ryhl <aliceryhl@google.com> wrote:
> > >
> > > This is needed to inline these helpers into Rust code.
> > >
> > > Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> > > Reviewed-by: Gary Guo <gary@garyguo.net>
> > > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> > > ---
> > > Cc: Paul Moore <paul@paul-moore.com>
> > > Cc: Serge Hallyn <sergeh@kernel.org>
> > > Cc: linux-security-module@vger.kernel.org
> > > ---
> > >  rust/helpers/cred.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > Acked-by: Paul Moore <paul@paul-moore.com>
>
> Ooops, sorry, I just saw that these were okay to merge into the
> various subsystem trees.  Merged into lsm/dev, thanks.

Thanks!

Re: [PATCH v2 00/27] Allow inlining C helpers into Rust when using LTO

[Miguel Ojeda]

On Mon, Jan 5, 2026 at 1:42 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
>       rust: bug: add __rust_helper to helpers
>       rust: err: add __rust_helper to helpers
>       rust: maple_tree: add __rust_helper to helpers
>       rust: mm: add __rust_helper to helpers
>       rust: of: add __rust_helper to helpers
>       rust: rbtree: add __rust_helper to helpers
>       rust: slab: add __rust_helper to helpers
>       rust: uaccess: add __rust_helper to helpers
>       rust: workqueue: add __rust_helper to helpers

Applied these to `rust-next` -- thanks everyone!

If someone did not intend for me to take it even if the Acked-by is
there (e.g. perhaps Andrew wanted to pick those nevertheless?), then
please shout.

With this, and if I didn't miss any message (plus looking at
linux-next where I see Greg picked usb), then only clk and jump_label
remain (plus any new incoming one).

Let's see if we can get them done next cycle then.

Cheers,
Miguel

Re: [PATCH v2 00/27] Allow inlining C helpers into Rust when using LTO

[Miguel Ojeda]

On Mon, Jan 5, 2026 at 1:42 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
>       rust: clk: add __rust_helper to helpers
>       rust: jump_label: add __rust_helper to helpers

Applied these to `rust-next` -- thanks everyone!

With these, the series is complete.

Cheers,
Miguel