Subject: Re: [PATCH v7 bpf-next 06/10] tracepoint: compute num_args at build time

From: Mathieu Desnoyers <[email-masked]>
Date: Wed, 28 Mar 2018 09:49:24 -0400 (EDT)

----- On Mar 27, 2018, at 10:11 PM, Alexei Starovoitov [email-masked] wrote:

> From: Alexei Starovoitov <[email-masked]>
> 
> compute number of arguments passed into tracepoint
> at compile time and store it as part of 'struct tracepoint'.
> The number is necessary to check safety of bpf program access that
> is coming in subsequent patch.

Hi Alexei,

Given that only eBPF needs this parameter count, we can move
it to the struct bpf_raw_event_map newly introduced by Steven,
right ? This would reduce bloat of struct tracepoint. For instance,
we don't need to keep this count around when eBPF is configured
out.

Thanks,

Mathieu

> 
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> Reviewed-by: Steven Rostedt (VMware) <[email-masked]>
> ---
> include/linux/tracepoint-defs.h |  1 +
> include/linux/tracepoint.h      | 12 ++++++------
> include/trace/define_trace.h    | 14 +++++++-------
> 3 files changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index 64ed7064f1fa..39a283c61c51 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -33,6 +33,7 @@ struct tracepoint {
> 	int (*regfunc)(void);
> 	void (*unregfunc)(void);
> 	struct tracepoint_func __rcu *funcs;
> +	u32 num_args;
> };
> 
> #endif
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index c94f466d57ef..c92f4adbc0d7 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -230,18 +230,18 @@ extern void syscall_unregfunc(void);
>  * structures, so we create an array of pointers that will be used for iteration
>  * on the tracepoints.
>  */
> -#define DEFINE_TRACE_FN(name, reg, unreg)				 \
> +#define DEFINE_TRACE_FN(name, reg, unreg, num_args)			 \
> 	static const char __tpstrtab_##name[]				 \
> 	__attribute__((section("__tracepoints_strings"))) = #name;	 \
> 	struct tracepoint __tracepoint_##name				 \
> 	__attribute__((section("__tracepoints"))) =			 \
> -		{ __tpstrtab_##name, STATIC_KEY_INIT_FALSE, reg, unreg, NULL };\
> +		{ __tpstrtab_##name, STATIC_KEY_INIT_FALSE, reg, unreg, NULL, num_args };\
> 	static struct tracepoint * const __tracepoint_ptr_##name __used	 \
> 	__attribute__((section("__tracepoints_ptrs"))) =		 \
> 		&__tracepoint_##name;
> 
> -#define DEFINE_TRACE(name)						\
> -	DEFINE_TRACE_FN(name, NULL, NULL);
> +#define DEFINE_TRACE(name, num_args)					\
> +	DEFINE_TRACE_FN(name, NULL, NULL, num_args);
> 
> #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)				\
> 	EXPORT_SYMBOL_GPL(__tracepoint_##name)
> @@ -275,8 +275,8 @@ extern void syscall_unregfunc(void);
> 		return false;						\
> 	}
> 
> -#define DEFINE_TRACE_FN(name, reg, unreg)
> -#define DEFINE_TRACE(name)
> +#define DEFINE_TRACE_FN(name, reg, unreg, num_args)
> +#define DEFINE_TRACE(name, num_args)
> #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
> #define EXPORT_TRACEPOINT_SYMBOL(name)
> 
> diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
> index d9e3d4aa3f6e..96b22ace9ae7 100644
> --- a/include/trace/define_trace.h
> +++ b/include/trace/define_trace.h
> @@ -25,7 +25,7 @@
> 
> #undef TRACE_EVENT
> #define TRACE_EVENT(name, proto, args, tstruct, assign, print)	\
> -	DEFINE_TRACE(name)
> +	DEFINE_TRACE(name, COUNT_ARGS(args))
> 
> #undef TRACE_EVENT_CONDITION
> #define TRACE_EVENT_CONDITION(name, proto, args, cond, tstruct, assign, print) \
> @@ -39,24 +39,24 @@
> #undef TRACE_EVENT_FN
> #define TRACE_EVENT_FN(name, proto, args, tstruct,		\
> 		assign, print, reg, unreg)			\
> -	DEFINE_TRACE_FN(name, reg, unreg)
> +	DEFINE_TRACE_FN(name, reg, unreg, COUNT_ARGS(args))
> 
> #undef TRACE_EVENT_FN_COND
> #define TRACE_EVENT_FN_COND(name, proto, args, cond, tstruct,		\
> 		assign, print, reg, unreg)			\
> -	DEFINE_TRACE_FN(name, reg, unreg)
> +	DEFINE_TRACE_FN(name, reg, unreg, COUNT_ARGS(args))
> 
> #undef DEFINE_EVENT
> #define DEFINE_EVENT(template, name, proto, args) \
> -	DEFINE_TRACE(name)
> +	DEFINE_TRACE(name, COUNT_ARGS(args))
> 
> #undef DEFINE_EVENT_FN
> #define DEFINE_EVENT_FN(template, name, proto, args, reg, unreg) \
> -	DEFINE_TRACE_FN(name, reg, unreg)
> +	DEFINE_TRACE_FN(name, reg, unreg, COUNT_ARGS(args))
> 
> #undef DEFINE_EVENT_PRINT
> #define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
> -	DEFINE_TRACE(name)
> +	DEFINE_TRACE(name, COUNT_ARGS(args))
> 
> #undef DEFINE_EVENT_CONDITION
> #define DEFINE_EVENT_CONDITION(template, name, proto, args, cond) \
> @@ -64,7 +64,7 @@
> 
> #undef DECLARE_TRACE
> #define DECLARE_TRACE(name, proto, args)	\
> -	DEFINE_TRACE(name)
> +	DEFINE_TRACE(name, COUNT_ARGS(args))
> 
> #undef TRACE_INCLUDE
> #undef __TRACE_INCLUDE
> --
> 2.9.5

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com