rust: cpufreq: Ensure C ABI compatibility in all unsafe

[PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

Posted by Abhinav Ananthu 3 months, 4 weeks ago

Update all `unsafe extern "C"` callback functions in the cpufreq module to
use `kernel::ffi` types (`c_int`, `c_uint`, etc.) instead of Rust-native
types like `i32`, `u32`, or `usize`.

This change ensures that all Rust callbacks have signatures that are
ABI-compatible with their corresponding C counterparts, which is critical
for FFI correctness and safety.

Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1170
Signed-off-by: Abhinav Ananthu <abhinav.ogl@gmail.com>
---
 rust/kernel/cpufreq.rs | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index 11b03e9d7e89..481a6d2dc362 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -1207,8 +1207,8 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn target_callback(
         ptr: *mut bindings::cpufreq_policy,
-        target_freq: u32,
-        relation: u32,
+        target_freq: c_uint,
+        relation: c_uint,
     ) -> kernel::ffi::c_int {
         from_result(|| {
             // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
@@ -1226,7 +1226,7 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn target_index_callback(
         ptr: *mut bindings::cpufreq_policy,
-        index: u32,
+        index: c_uint,
     ) -> kernel::ffi::c_int {
         from_result(|| {
             // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
@@ -1249,7 +1249,7 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn fast_switch_callback(
         ptr: *mut bindings::cpufreq_policy,
-        target_freq: u32,
+        target_freq: c_uint,
     ) -> kernel::ffi::c_uint {
         // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
         // lifetime of `policy`.
@@ -1263,10 +1263,10 @@ impl<T: Driver> Registration<T> {
     ///
     /// - This function may only be called from the cpufreq C infrastructure.
     unsafe extern "C" fn adjust_perf_callback(
-        cpu: u32,
-        min_perf: usize,
-        target_perf: usize,
-        capacity: usize,
+        cpu: c_uint,
+        min_perf: c_ulong,
+        target_perf: c_ulong,
+        capacity: c_ulong,
     ) {
         // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number.
         let cpu_id = unsafe { CpuId::from_u32_unchecked(cpu) };
@@ -1284,7 +1284,7 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn get_intermediate_callback(
         ptr: *mut bindings::cpufreq_policy,
-        index: u32,
+        index: c_uint,
     ) -> kernel::ffi::c_uint {
         // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
         // lifetime of `policy`.
@@ -1305,7 +1305,7 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn target_intermediate_callback(
         ptr: *mut bindings::cpufreq_policy,
-        index: u32,
+        index: c_uint,
     ) -> kernel::ffi::c_int {
         from_result(|| {
             // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
@@ -1325,7 +1325,7 @@ impl<T: Driver> Registration<T> {
     /// # Safety
     ///
     /// - This function may only be called from the cpufreq C infrastructure.
-    unsafe extern "C" fn get_callback(cpu: u32) -> kernel::ffi::c_uint {
+    unsafe extern "C" fn get_callback(cpu: c_uint) -> kernel::ffi::c_uint {
         // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number.
         let cpu_id = unsafe { CpuId::from_u32_unchecked(cpu) };
 
@@ -1351,7 +1351,7 @@ impl<T: Driver> Registration<T> {
     ///
     /// - This function may only be called from the cpufreq C infrastructure.
     /// - The pointer arguments must be valid pointers.
-    unsafe extern "C" fn bios_limit_callback(cpu: i32, limit: *mut u32) -> kernel::ffi::c_int {
+    unsafe extern "C" fn bios_limit_callback(cpu: c_int, limit: *mut c_uint) -> kernel::ffi::c_int {
         // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number.
         let cpu_id = unsafe { CpuId::from_i32_unchecked(cpu) };
 
@@ -1371,7 +1371,7 @@ impl<T: Driver> Registration<T> {
     /// - The pointer arguments must be valid pointers.
     unsafe extern "C" fn set_boost_callback(
         ptr: *mut bindings::cpufreq_policy,
-        state: i32,
+        state: c_int,
     ) -> kernel::ffi::c_int {
         from_result(|| {
             // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
-- 
2.34.1

Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

Posted by Viresh Kumar 3 months, 3 weeks ago

On 13-06-25, 15:48, Abhinav Ananthu wrote:
> Update all `unsafe extern "C"` callback functions in the cpufreq module to
> use `kernel::ffi` types (`c_int`, `c_uint`, etc.) instead of Rust-native
> types like `i32`, `u32`, or `usize`.
> 
> This change ensures that all Rust callbacks have signatures that are
> ABI-compatible with their corresponding C counterparts, which is critical
> for FFI correctness and safety.
> 
> Suggested-by: Miguel Ojeda <ojeda@kernel.org>
> Link: https://github.com/Rust-for-Linux/linux/issues/1170
> Signed-off-by: Abhinav Ananthu <abhinav.ogl@gmail.com>
> ---
>  rust/kernel/cpufreq.rs | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)

Applied. Thanks.

There are few users of kernel::ffi::* in cpufreq.rs and opp.rs, if you want to
convert them as well.

-- 
viresh

Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

Posted by Viresh Kumar 3 months, 3 weeks ago

On 13-06-25, 15:48, Abhinav Ananthu wrote:
> Update all `unsafe extern "C"` callback functions in the cpufreq module to
> use `kernel::ffi` types (`c_int`, `c_uint`, etc.) instead of Rust-native
> types like `i32`, `u32`, or `usize`.
> 
> This change ensures that all Rust callbacks have signatures that are
> ABI-compatible with their corresponding C counterparts, which is critical
> for FFI correctness and safety.
> 
> Suggested-by: Miguel Ojeda <ojeda@kernel.org>
> Link: https://github.com/Rust-for-Linux/linux/issues/1170
> Signed-off-by: Abhinav Ananthu <abhinav.ogl@gmail.com>
> ---
>  rust/kernel/cpufreq.rs | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
> index 11b03e9d7e89..481a6d2dc362 100644
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -1207,8 +1207,8 @@ impl<T: Driver> Registration<T> {
>      /// - The pointer arguments must be valid pointers.
>      unsafe extern "C" fn target_callback(
>          ptr: *mut bindings::cpufreq_policy,
> -        target_freq: u32,
> -        relation: u32,
> +        target_freq: c_uint,
> +        relation: c_uint,

I think the one in prelude points to core::ffi::* instead, while we
want to use kernel::ffi::* ?

Miguel ?

Also why does prelude use ::ffi::* instead of kernel::ffi::* ? I was always a
bit confused about it.

-- 
viresh

Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

Posted by Miguel Ojeda 3 months, 3 weeks ago

On Thu, Jun 19, 2025 at 8:57 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> I think the one in prelude points to core::ffi::* instead, while we
> want to use kernel::ffi::* ?
>
> Miguel ?

The one in the `kernel` prelude points to the kernel ones (the core
ones should not be used anymore).

> Also why does prelude use ::ffi::* instead of kernel::ffi::* ? I was always a
> bit confused about it.

It is because we define them in a crate called `ffi`, not in the
`kernel` one; and we also re-export it in `kernel`.

In any case, from now on, one should just refer to them directly as
`c_*` (please use the `kernel` prelude for that) -- please see:

    https://docs.kernel.org/rust/coding-guidelines.html#c-ffi-types

I hope that helps!

Cheers,
Miguel

Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

Posted by Viresh Kumar 3 months, 3 weeks ago

On 19-06-25, 09:32, Miguel Ojeda wrote:
> In any case, from now on, one should just refer to them directly as
> `c_*` (please use the `kernel` prelude for that) -- please see:
> 
>     https://docs.kernel.org/rust/coding-guidelines.html#c-ffi-types
> 
> I hope that helps!

Thanks.

-- 
viresh