Re: [PATCH v3 2/2] rust: add tracepoint support

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Jun 21, 2024 at 12:35 PM Alice Ryhl <aliceryhl@google.com> 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@google.com>
> ---
>  include/linux/tracepoint.h      | 18 +++++++++++++++-
>  include/trace/define_trace.h    |  7 ++++++
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/lib.rs              |  1 +
>  rust/kernel/tracepoint.rs       | 47 +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 73 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 689b6d71590e..d82af4d77c9f 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -238,6 +238,20 @@ 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_REAL(name, proto, args)                   \
> +       notrace void rust_do_trace_##name(proto)                        \
> +       {                                                               \
> +               __DO_TRACE(name,                                        \
> +                       TP_ARGS(args),                                  \
> +                       cpu_online(raw_smp_processor_id()), 0);         \
> +       }
> +
>  /*
>   * Make sure the alignment of the structure in the __tracepoints section will
>   * not add unwanted padding between the beginning of the section and the
> @@ -253,6 +267,7 @@ 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 trace_##name(proto)                          \
>         {                                                               \
>                 if (static_key_false(&__tracepoint_##name.key))         \
> @@ -337,7 +352,8 @@ 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..b47cc036acba 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_REAL(name, PARAMS(proto), PARAMS(args))
> +#endif
> +
>  #undef TRACE_INCLUDE
>  #undef __TRACE_INCLUDE
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h

Hmm, I tried using the support where I have both events and hooks:

#define CREATE_TRACE_POINTS
#define CREATE_RUST_TRACE_POINTS
#include <trace/hooks/rust_binder.h>
#include <trace/events/rust_binder.h>

But it's not really working. Initially I thought that it's because I
need to undef DEFINE_RUST_DO_TRACE at the end of this file, but even
when I added that, I still get this error:

    error: redefinition of 'str__rust_binder__trace_system_name'

Is the Rust support missing something, or is the answer just that you
can't have two files of the same name like this? Or am I doing
something else wrong?

Alice