netdev - Re: [PATCH 1/3] bpf: support writable context for bare tracepoint

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Date:   Thu, 16 Sep 2021 16:16:58 -0700
From:   Yonghong Song <yhs@...com>
To:     Hou Tao <houtao1@...wei.com>, Alexei Starovoitov <ast@...nel.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3] bpf: support writable context for bare tracepoint



On 9/16/21 6:55 AM, Hou Tao wrote:
> Commit 9df1c28bb752 ("bpf: add writable context for raw tracepoints")
> supports writable context for tracepoint, but it misses the support
> for bare tracepoint which has no associated trace event.
> 
> Bare tracepoint is defined by DECLARE_TRACE(), so adding a corresponding
> DECLARE_TRACE_WRITABLE() macro to generate a definition in __bpf_raw_tp_map
> section for bare tracepoint in a similar way to DEFINE_TRACE_WRITABLE().
> 
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>   include/trace/bpf_probe.h | 19 +++++++++++++++----
>   1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index a23be89119aa..d08ee1060d82 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -93,8 +93,7 @@ __section("__bpf_raw_tp_map") = {					\
>   
>   #define FIRST(x, ...) x
>   
> -#undef DEFINE_EVENT_WRITABLE
> -#define DEFINE_EVENT_WRITABLE(template, call, proto, args, size)	\
> +#define __CHECK_WRITABLE_BUF_SIZE(call, proto, args, size)		\
>   static inline void bpf_test_buffer_##call(void)				\
>   {									\
>   	/* BUILD_BUG_ON() is ignored if the code is completely eliminated, but \
> @@ -103,8 +102,12 @@ static inline void bpf_test_buffer_##call(void)				\
>   	 */								\
>   	FIRST(proto);							\
>   	(void)BUILD_BUG_ON_ZERO(size != sizeof(*FIRST(args)));		\
> -}									\
> -__DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
> +}
> +
> +#undef DEFINE_EVENT_WRITABLE
> +#define DEFINE_EVENT_WRITABLE(template, call, proto, args, size) \
> +	__CHECK_WRITABLE_BUF_SIZE(call, PARAMS(proto), PARAMS(args), size) \
> +	__DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
>   
>   #undef DEFINE_EVENT
>   #define DEFINE_EVENT(template, call, proto, args)			\
> @@ -119,10 +122,18 @@ __DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
>   	__BPF_DECLARE_TRACE(call, PARAMS(proto), PARAMS(args))		\
>   	__DEFINE_EVENT(call, call, PARAMS(proto), PARAMS(args), 0)
>   
> +#undef DECLARE_TRACE_WRITABLE
> +#define DECLARE_TRACE_WRITABLE(call, proto, args, size) \
> +	__CHECK_WRITABLE_BUF_SIZE(call, PARAMS(proto), PARAMS(args), size) \
> +	__BPF_DECLARE_TRACE(call, PARAMS(proto), PARAMS(args)) \
> +	__DEFINE_EVENT(call, call, PARAMS(proto), PARAMS(args), size)
> +
>   #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
>   
>   #undef DEFINE_EVENT_WRITABLE
> +#undef DECLARE_TRACE_WRITABLE
>   #undef __DEFINE_EVENT
> +#undef __CHECK_WRITABLE_BUF_SIZE

Put "#undef __CHECK_WRITABLE_BUF_SIZE" right after "#undef 
DECLARE_TRACE_WRITABLE" since they are related to each other
and also they are in correct reverse order w.r.t. __DEFINE_EVENT?

>   #undef FIRST
>   
>   #endif /* CONFIG_BPF_EVENTS */
>