diff options
| author | Christian Brauner <brauner@kernel.org> | 2025-12-04 11:04:24 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2025-12-15 14:13:04 +0100 |
| commit | 5334fc280735dcf5882511a219a99b5759e14870 (patch) | |
| tree | 8ce87aa5d4c2a49a6623971d47e6bef9e4b11692 | |
| parent | 8f0b4cce4481fb22653697cced8d0d04027cb1e8 (diff) | |
| parent | 268eaa8ab4ace3f3bc80fd91bb461e6b6c9da29e (diff) | |
| download | vfs-7.0.rust.tar.gz | |
Merge patch series "Allow inlining C helpers into Rust when using LTO"vfs-7.0.rust
Alice Ryhl <aliceryhl@google.com> says:
This patch series adds __rust_helper to every single rust helper.
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.
* patches from https://patch.msgid.link/20251202-define-rust-helper-v1-0-a2e13cbc17a6@google.com:
rust: poll: add __rust_helper to helpers
rust: pid_namespace: add __rust_helper to helpers
rust: fs: add __rust_helper to helpers
Link: https://patch.msgid.link/20251202-define-rust-helper-v1-0-a2e13cbc17a6@google.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
| -rw-r--r-- | rust/helpers/fs.c | 2 | ||||
| -rw-r--r-- | rust/helpers/pid_namespace.c | 8 | ||||
| -rw-r--r-- | rust/helpers/poll.c | 5 |
3 files changed, 9 insertions, 6 deletions
diff --git a/rust/helpers/fs.c b/rust/helpers/fs.c index a75c9676337246..789d60fb8908b9 100644 --- a/rust/helpers/fs.c +++ b/rust/helpers/fs.c @@ -6,7 +6,7 @@ #include <linux/fs.h> -struct file *rust_helper_get_file(struct file *f) +__rust_helper struct file *rust_helper_get_file(struct file *f) { return get_file(f); } diff --git a/rust/helpers/pid_namespace.c b/rust/helpers/pid_namespace.c index f41482bdec9a7c..f46ab779b5279f 100644 --- a/rust/helpers/pid_namespace.c +++ b/rust/helpers/pid_namespace.c @@ -3,18 +3,20 @@ #include <linux/pid_namespace.h> #include <linux/cleanup.h> -struct pid_namespace *rust_helper_get_pid_ns(struct pid_namespace *ns) +__rust_helper struct pid_namespace * +rust_helper_get_pid_ns(struct pid_namespace *ns) { return get_pid_ns(ns); } -void rust_helper_put_pid_ns(struct pid_namespace *ns) +__rust_helper void rust_helper_put_pid_ns(struct pid_namespace *ns) { put_pid_ns(ns); } /* Get a reference on a task's pid namespace. */ -struct pid_namespace *rust_helper_task_get_pid_ns(struct task_struct *task) +__rust_helper struct pid_namespace * +rust_helper_task_get_pid_ns(struct task_struct *task) { struct pid_namespace *pid_ns; diff --git a/rust/helpers/poll.c b/rust/helpers/poll.c index 7e5b1751c2d526..78b3839b50f065 100644 --- a/rust/helpers/poll.c +++ b/rust/helpers/poll.c @@ -3,8 +3,9 @@ #include <linux/export.h> #include <linux/poll.h> -void rust_helper_poll_wait(struct file *filp, wait_queue_head_t *wait_address, - poll_table *p) +__rust_helper void rust_helper_poll_wait(struct file *filp, + wait_queue_head_t *wait_address, + poll_table *p) { poll_wait(filp, wait_address, p); } |