[PATCH 00/46] Allow inlining C helpers into Rust when using LTO

[PATCH 00/46] 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>
---
Alice Ryhl (46):
      rust: auxiliary: add __rust_helper to helpers
      rust: barrier: add __rust_helper to helpers
      rust: binder: add __rust_helper to helpers
      rust: bitmap: add __rust_helper to helpers
      rust: bitops: 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: cpufreq: add __rust_helper to helpers
      rust: cpumask: add __rust_helper to helpers
      rust: cred: add __rust_helper to helpers
      rust: device: add __rust_helper to helpers
      rust: dma: add __rust_helper to helpers
      rust: drm: add __rust_helper to helpers
      rust: err: add __rust_helper to helpers
      rust: fs: add __rust_helper to helpers
      rust: io: add __rust_helper to helpers
      rust: irq: add __rust_helper to helpers
      rust: jump_label: add __rust_helper to helpers
      rust: kunit: 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: pci: add __rust_helper to helpers
      rust: pid_namespace: add __rust_helper to helpers
      rust: platform: add __rust_helper to helpers
      rust: poll: add __rust_helper to helpers
      rust: processor: add __rust_helper to helpers
      rust: property: 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: regulator: add __rust_helper to helpers
      rust: scatterlist: 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/auxiliary.c     |  6 +++--
 rust/helpers/barrier.c       |  6 ++---
 rust/helpers/binder.c        | 13 ++++-----
 rust/helpers/bitmap.c        |  6 +++--
 rust/helpers/bitops.c        | 11 +++++---
 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/cpufreq.c       |  3 ++-
 rust/helpers/cpumask.c       | 32 +++++++++++++---------
 rust/helpers/cred.c          |  4 +--
 rust/helpers/device.c        | 16 +++++------
 rust/helpers/dma.c           | 15 ++++++-----
 rust/helpers/drm.c           |  7 ++---
 rust/helpers/err.c           |  6 ++---
 rust/helpers/fs.c            |  2 +-
 rust/helpers/io.c            | 64 +++++++++++++++++++++++---------------------
 rust/helpers/irq.c           |  6 +++--
 rust/helpers/jump_label.c    |  2 +-
 rust/helpers/kunit.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/pci.c           | 13 +++++----
 rust/helpers/pid_namespace.c |  8 +++---
 rust/helpers/platform.c      |  2 +-
 rust/helpers/poll.c          |  5 ++--
 rust/helpers/processor.c     |  2 +-
 rust/helpers/property.c      |  2 +-
 rust/helpers/rbtree.c        |  5 ++--
 rust/helpers/rcu.c           |  4 +--
 rust/helpers/refcount.c      | 10 +++----
 rust/helpers/regulator.c     | 24 ++++++++++-------
 rust/helpers/scatterlist.c   | 12 +++++----
 rust/helpers/security.c      | 26 ++++++++++--------
 rust/helpers/signal.c        |  2 +-
 rust/helpers/slab.c          | 14 +++++-----
 rust/helpers/spinlock.c      | 13 ++++-----
 rust/helpers/sync.c          |  4 +--
 rust/helpers/task.c          | 24 ++++++++---------
 rust/helpers/time.c          | 12 ++++-----
 rust/helpers/uaccess.c       |  8 +++---
 rust/helpers/usb.c           |  3 ++-
 rust/helpers/vmalloc.c       |  7 ++---
 rust/helpers/wait.c          |  2 +-
 rust/helpers/workqueue.c     |  8 +++---
 rust/helpers/xarray.c        | 10 +++----
 52 files changed, 280 insertions(+), 226 deletions(-)
---
base-commit: 54e3eae855629702c566bd2e130d9f40e7f35bde
change-id: 20251202-define-rust-helper-f7b531813007

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

[PATCH 13/46] rust: cred: add __rust_helper to helpers

[Alice Ryhl]

This is needed to inline these helpers into Rust code.

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);
 }

-- 
2.52.0.158.g65b55ccf14-goog

[PATCH 37/46] rust: security: add __rust_helper to helpers

[Alice Ryhl]

This is needed to inline these helpers into Rust code.

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);
 }

-- 
2.52.0.158.g65b55ccf14-goog

Re: [PATCH 00/46] Allow inlining C helpers into Rust when using LTO

[Boqun Feng]

On Tue, Dec 02, 2025 at 07:37:24PM +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.
> 
> 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>

For the whole series:

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> ---
[...]

Re: [PATCH 00/46] Allow inlining C helpers into Rust when using LTO

[Gary Guo]

On Tue, 02 Dec 2025 19:37:24 +0000
Alice Ryhl <aliceryhl@google.com> 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.
> 
> 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>
> ---
> Alice Ryhl (46):
>       rust: auxiliary: add __rust_helper to helpers
>       rust: barrier: add __rust_helper to helpers
>       rust: binder: add __rust_helper to helpers
>       rust: bitmap: add __rust_helper to helpers
>       rust: bitops: 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: cpufreq: add __rust_helper to helpers
>       rust: cpumask: add __rust_helper to helpers
>       rust: cred: add __rust_helper to helpers
>       rust: device: add __rust_helper to helpers
>       rust: dma: add __rust_helper to helpers
>       rust: drm: add __rust_helper to helpers
>       rust: err: add __rust_helper to helpers
>       rust: fs: add __rust_helper to helpers
>       rust: io: add __rust_helper to helpers
>       rust: irq: add __rust_helper to helpers
>       rust: jump_label: add __rust_helper to helpers
>       rust: kunit: 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: pci: add __rust_helper to helpers
>       rust: pid_namespace: add __rust_helper to helpers
>       rust: platform: add __rust_helper to helpers
>       rust: poll: add __rust_helper to helpers
>       rust: processor: add __rust_helper to helpers
>       rust: property: 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: regulator: add __rust_helper to helpers
>       rust: scatterlist: 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

Thansk for sending this Alice! With this series in first, my series for
inlining helpers should be much easier to apply.

For the whole series:

Reviewed-by: Gary Guo <gary@garyguo.net>

Best,
Gary


> 
>  rust/helpers/auxiliary.c     |  6 +++--
>  rust/helpers/barrier.c       |  6 ++---
>  rust/helpers/binder.c        | 13 ++++-----
>  rust/helpers/bitmap.c        |  6 +++--
>  rust/helpers/bitops.c        | 11 +++++---
>  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/cpufreq.c       |  3 ++-
>  rust/helpers/cpumask.c       | 32 +++++++++++++---------
>  rust/helpers/cred.c          |  4 +--
>  rust/helpers/device.c        | 16 +++++------
>  rust/helpers/dma.c           | 15 ++++++-----
>  rust/helpers/drm.c           |  7 ++---
>  rust/helpers/err.c           |  6 ++---
>  rust/helpers/fs.c            |  2 +-
>  rust/helpers/io.c            | 64 +++++++++++++++++++++++---------------------
>  rust/helpers/irq.c           |  6 +++--
>  rust/helpers/jump_label.c    |  2 +-
>  rust/helpers/kunit.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/pci.c           | 13 +++++----
>  rust/helpers/pid_namespace.c |  8 +++---
>  rust/helpers/platform.c      |  2 +-
>  rust/helpers/poll.c          |  5 ++--
>  rust/helpers/processor.c     |  2 +-
>  rust/helpers/property.c      |  2 +-
>  rust/helpers/rbtree.c        |  5 ++--
>  rust/helpers/rcu.c           |  4 +--
>  rust/helpers/refcount.c      | 10 +++----
>  rust/helpers/regulator.c     | 24 ++++++++++-------
>  rust/helpers/scatterlist.c   | 12 +++++----
>  rust/helpers/security.c      | 26 ++++++++++--------
>  rust/helpers/signal.c        |  2 +-
>  rust/helpers/slab.c          | 14 +++++-----
>  rust/helpers/spinlock.c      | 13 ++++-----
>  rust/helpers/sync.c          |  4 +--
>  rust/helpers/task.c          | 24 ++++++++---------
>  rust/helpers/time.c          | 12 ++++-----
>  rust/helpers/uaccess.c       |  8 +++---
>  rust/helpers/usb.c           |  3 ++-
>  rust/helpers/vmalloc.c       |  7 ++---
>  rust/helpers/wait.c          |  2 +-
>  rust/helpers/workqueue.c     |  8 +++---
>  rust/helpers/xarray.c        | 10 +++----
>  52 files changed, 280 insertions(+), 226 deletions(-)
> ---
> base-commit: 54e3eae855629702c566bd2e130d9f40e7f35bde
> change-id: 20251202-define-rust-helper-f7b531813007
> 
> Best regards,

Re: (subset) [PATCH 00/46] Allow inlining C helpers into Rust when using LTO

[Christian Brauner]

On Tue, 02 Dec 2025 19:37:24 +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.
> 
> These changes were generated by adding __rust_helper and running
> ClangFormat. Unrelated formatting changes were removed manually.
> 
> [...]

Applied to the vfs-6.20.rust branch of the vfs/vfs.git tree.
Patches in the vfs-6.20.rust branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.20.rust

[18/46] rust: fs: add __rust_helper to helpers
        https://git.kernel.org/vfs/vfs/c/02c444cc60e5
[27/46] rust: pid_namespace: add __rust_helper to helpers
        https://git.kernel.org/vfs/vfs/c/f28a178408e4
[29/46] rust: poll: add __rust_helper to helpers
        https://git.kernel.org/vfs/vfs/c/de98ed59d678