Re: [PATCH v8 2/5] rust: add tracepoint support

[Boqun Feng <boqun.feng@gmail.com>]

On Thu, Aug 22, 2024 at 12:04:14PM +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.
> 
> Instead of calling __DO_TRACE directly, the exported rust_do_trace_
> function calls an inline helper function. This is because the `cond`
> argument does not exist at the callsite of DEFINE_RUST_DO_TRACE.
> 
> __DECLARE_TRACE always emits an inline static and an extern declaration
> that is only used when CREATE_RUST_TRACE_POINTS is set. These should not
> end up in the final binary so it is not a problem that they sometimes
> are emitted without a user.
> 
> Reviewed-by: Carlos Llamas <cmllamas@google.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

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

Regards,
Boqun

> ---
>  include/linux/tracepoint.h      | 22 +++++++++++++++++-
>  include/trace/define_trace.h    | 12 ++++++++++
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/lib.rs              |  1 +
>  rust/kernel/tracepoint.rs       | 49 +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 84 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 6be396bb4297..5042ca588e41 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -237,6 +237,18 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  #define __DECLARE_TRACE_RCU(name, proto, args, cond)
>  #endif
>  
> +/*
> + * Declare an exported function that Rust code can call to trigger this
> + * tracepoint. This function does not include the static branch; that is done
> + * in Rust to avoid a function call when the tracepoint is disabled.
> + */
> +#define DEFINE_RUST_DO_TRACE(name, proto, args)
> +#define __DEFINE_RUST_DO_TRACE(name, proto, args)			\
> +	notrace void rust_do_trace_##name(proto)			\
> +	{								\
> +		__rust_do_trace_##name(args);				\
> +	}
> +
>  /*
>   * Make sure the alignment of the structure in the __tracepoints section will
>   * not add unwanted padding between the beginning of the section and the
> @@ -252,6 +264,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  	extern int __traceiter_##name(data_proto);			\
>  	DECLARE_STATIC_CALL(tp_func_##name, __traceiter_##name);	\
>  	extern struct tracepoint __tracepoint_##name;			\
> +	extern void rust_do_trace_##name(proto);			\
> +	static inline void __rust_do_trace_##name(proto)		\
> +	{								\
> +		__DO_TRACE(name,					\
> +			TP_ARGS(args),					\
> +			TP_CONDITION(cond), 0);				\
> +	}								\
>  	static inline void trace_##name(proto)				\
>  	{								\
>  		if (static_key_false(&__tracepoint_##name.key))		\
> @@ -336,7 +355,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  	void __probestub_##_name(void *__data, proto)			\
>  	{								\
>  	}								\
> -	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
> +	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);	\
> +	DEFINE_RUST_DO_TRACE(_name, TP_PROTO(proto), TP_ARGS(args))
>  
>  #define DEFINE_TRACE(name, proto, args)		\
>  	DEFINE_TRACE_FN(name, NULL, NULL, PARAMS(proto), PARAMS(args));
> diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
> index 00723935dcc7..8159294c2041 100644
> --- a/include/trace/define_trace.h
> +++ b/include/trace/define_trace.h
> @@ -72,6 +72,13 @@
>  #define DECLARE_TRACE(name, proto, args)	\
>  	DEFINE_TRACE(name, PARAMS(proto), PARAMS(args))
>  
> +/* If requested, create helpers for calling these tracepoints from Rust. */
> +#ifdef CREATE_RUST_TRACE_POINTS
> +#undef DEFINE_RUST_DO_TRACE
> +#define DEFINE_RUST_DO_TRACE(name, proto, args)	\
> +	__DEFINE_RUST_DO_TRACE(name, PARAMS(proto), PARAMS(args))
> +#endif
> +
>  #undef TRACE_INCLUDE
>  #undef __TRACE_INCLUDE
>  
> @@ -129,6 +136,11 @@
>  # undef UNDEF_TRACE_INCLUDE_PATH
>  #endif
>  
> +#ifdef CREATE_RUST_TRACE_POINTS
> +# undef DEFINE_RUST_DO_TRACE
> +# define DEFINE_RUST_DO_TRACE(name, proto, args)
> +#endif
> +
>  /* We may be processing more files */
>  #define CREATE_TRACE_POINTS
>  
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 8fd092e1b809..fc6f94729789 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -20,6 +20,7 @@
>  #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/kernel/lib.rs b/rust/kernel/lib.rs
> index 91af9f75d121..d00a44b000b6 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -51,6 +51,7 @@
>  pub mod sync;
>  pub mod task;
>  pub mod time;
> +pub mod tracepoint;
>  pub mod types;
>  pub mod uaccess;
>  pub mod workqueue;
> diff --git a/rust/kernel/tracepoint.rs b/rust/kernel/tracepoint.rs
> new file mode 100644
> index 000000000000..cf2d9ad15912
> --- /dev/null
> +++ b/rust/kernel/tracepoint.rs
> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Logic for tracepoints.
> +
> +/// Declare the Rust entry point for a tracepoint.
> +///
> +/// This macro generates an unsafe function that calls into C, and its safety requirements will be
> +/// whatever the relevant C code requires. To document these safety requirements, you may add
> +/// doc-comments when invoking the macro.
> +#[macro_export]
> +macro_rules! declare_trace {
> +    ($($(#[$attr:meta])* $pub:vis unsafe fn $name:ident($($argname:ident : $argtyp:ty),* $(,)?);)*) => {$(
> +        $( #[$attr] )*
> +        #[inline(always)]
> +        $pub unsafe fn $name($($argname : $argtyp),*) {
> +            #[cfg(CONFIG_TRACEPOINTS)]
> +            {
> +                // SAFETY: It's always okay to query the static key for a tracepoint.
> +                let should_trace = unsafe {
> +                    $crate::macros::paste! {
> +                        $crate::jump_label::static_key_false!(
> +                            $crate::bindings::[< __tracepoint_ $name >],
> +                            $crate::bindings::tracepoint,
> +                            key
> +                        )
> +                    }
> +                };
> +
> +                if should_trace {
> +                    $crate::macros::paste! {
> +                        // SAFETY: The caller guarantees that it is okay to call this tracepoint.
> +                        unsafe { $crate::bindings::[< rust_do_trace_ $name >]($($argname),*) };
> +                    }
> +                }
> +            }
> +
> +            #[cfg(not(CONFIG_TRACEPOINTS))]
> +            {
> +                // If tracepoints are disabled, insert a trivial use of each argument
> +                // to avoid unused argument warnings.
> +                $( let _unused = $argname; )*
> +            }
> +        }
> +    )*}
> +}
> +
> +pub use declare_trace;
> 
> -- 
> 2.46.0.184.g6999bdac58-goog
>