Re: [PATCH 3/3] rust: add tracepoint support

[Peter Zijlstra]

On Thu, Jun 06, 2024 at 03:05:26PM +0000, Alice Ryhl wrote:
> Make it possible to have Rust code call into tracepoints defined by C
> code. It is still required that the tracepoint is declared in a C
> header, and that this header is included in the input to bindgen.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/bindings/lib.rs            | 15 +++++++
>  rust/helpers.c                  | 24 +++++++++++
>  rust/kernel/lib.rs              |  1 +
>  rust/kernel/tracepoint.rs       | 92 +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 133 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index ddb5644d4fd9..d442f9ccfc2c 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -15,6 +15,7 @@
>  #include <linux/refcount.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> +#include <linux/tracepoint.h>
>  #include <linux/wait.h>
>  #include <linux/workqueue.h>
>  
> diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
> index 40ddaee50d8b..48856761d682 100644
> --- a/rust/bindings/lib.rs
> +++ b/rust/bindings/lib.rs
> @@ -48,3 +48,18 @@ mod bindings_helper {
>  }
>  
>  pub use bindings_raw::*;
> +
> +/// Rust version of the C macro `rcu_dereference_raw`.
> +///
> +/// The rust helper only works with void pointers, but this wrapper method makes it work with any
> +/// pointer type using pointer casts.
> +///
> +/// # Safety
> +///
> +/// This method has the same safety requirements as the C macro of the same name.
> +#[inline(always)]
> +pub unsafe fn rcu_dereference_raw<T>(p: *const *mut T) -> *mut T {
> +    // SAFETY: This helper calls into the C macro, so the caller promises to uphold the safety
> +    // requirements.
> +    unsafe { __rcu_dereference_raw(p as *mut *mut _) as *mut T }
> +}
> diff --git a/rust/helpers.c b/rust/helpers.c
> index 2c37a0f5d7a8..0560cc2a512a 100644
> --- a/rust/helpers.c
> +++ b/rust/helpers.c
> @@ -165,6 +165,30 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
>  }
>  EXPORT_SYMBOL_GPL(rust_helper_krealloc);
>  
> +void rust_helper_preempt_enable_notrace(void)
> +{
> +	preempt_enable_notrace();
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_preempt_enable_notrace);
> +
> +void rust_helper_preempt_disable_notrace(void)
> +{
> +	preempt_disable_notrace();
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_preempt_disable_notrace);

A notrace wrapper that is tracable, lol.

> +bool rust_helper_current_cpu_online(void)
> +{
> +	return cpu_online(raw_smp_processor_id());
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_current_cpu_online);
> +
> +void *rust_helper___rcu_dereference_raw(void **p)
> +{
> +	return rcu_dereference_raw(p);
> +}
> +EXPORT_SYMBOL_GPL(rust_helper___rcu_dereference_raw);

I'm going to keep yelling and objecting to these wrappers.

Fix bindgen already. Or whatever is needed to get it to interoperate
with C inline / asm.

NAK NAK NAK