[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 06/46] rust: blk: 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: Andreas Hindborg <a.hindborg@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-block@vger.kernel.org
---
 rust/helpers/blk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/helpers/blk.c b/rust/helpers/blk.c
index cc9f4e6a2d2346eb2814104cce706755ba135e06..20c512e46a7a5fd126d092a5b9f8742a1deac9ff 100644
--- a/rust/helpers/blk.c
+++ b/rust/helpers/blk.c
@@ -3,12 +3,12 @@
 #include <linux/blk-mq.h>
 #include <linux/blkdev.h>
 
-void *rust_helper_blk_mq_rq_to_pdu(struct request *rq)
+__rust_helper void *rust_helper_blk_mq_rq_to_pdu(struct request *rq)
 {
 	return blk_mq_rq_to_pdu(rq);
 }
 
-struct request *rust_helper_blk_mq_rq_from_pdu(void *pdu)
+__rust_helper struct request *rust_helper_blk_mq_rq_from_pdu(void *pdu)
 {
 	return blk_mq_rq_from_pdu(pdu);
 }

-- 
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