Re: [PATCH v2 bpf-next 5/8] bpf: introduce BPF_RAW_TRACEPOINT

On Sat, 24 Mar 2018 00:13:28 +0100
Daniel Borkmann [off-list ref] wrote:

#define UNPACK(...)			__VA_ARGS__
#define REPEAT_1(FN, DL, X, ...)	FN(X)
#define REPEAT_2(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_1(FN, DL, __VA_ARGS__)
#define REPEAT_3(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_2(FN, DL, __VA_ARGS__)
#define REPEAT_4(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_3(FN, DL, __VA_ARGS__)
#define REPEAT_5(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_4(FN, DL, __VA_ARGS__)
#define REPEAT_6(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_5(FN, DL, __VA_ARGS__)
#define REPEAT_7(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_6(FN, DL, __VA_ARGS__)
#define REPEAT_8(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_7(FN, DL, __VA_ARGS__)
#define REPEAT_9(FN, DL, X, ...)	FN(X) UNPACK DL REPEAT_8(FN, DL, __VA_ARGS__)
#define REPEAT(X, FN, DL, ...)		REPEAT_##X(FN, DL, __VA_ARGS__)

#define SARG(X)		u64 arg##X
#define COPY(X)		args[X] = arg##X

#define __DL_COM	(,)
#define __DL_SEM	(;)

#define __SEQ		0, 1, 2, 3, 4, 5, 6, 7, 8, 9

#define BPF_TRACE_DECL_x(x)						\
	void bpf_trace_run##x(struct bpf_prog *prog,			\
			      REPEAT(x, SARG, __DL_COM, __SEQ))
#define BPF_TRACE_DEFN_x(x)						\
	void bpf_trace_run##x(struct bpf_prog *prog,			\
			      REPEAT(x, SARG, __DL_COM, __SEQ))		\
	{								\
		u64 args[x];						\
		REPEAT(x, COPY, __DL_SEM, __SEQ);			\
		__bpf_trace_run(prog, args);				\
	}								\
	EXPORT_SYMBOL_GPL(bpf_trace_run##x)

So doing a ...

BPF_TRACE_DECL_x(5);
BPF_TRACE_DEFN_x(5);

... will generate in kernel/trace/bpf_trace.i:

void bpf_foo_trace_run5(struct bpf_prog *prog, u64 arg0 , u64 arg1 , u64 arg2 , u64 arg3 , u64 arg4);
void bpf_foo_trace_run5(struct bpf_prog *prog, u64 arg0 , u64 arg1 , u64 arg2 , u64 arg3 , u64 arg4)
{
	u64 args[5];
	args[0] = arg0 ;
	args[1] = arg1 ;
	args[2] = arg2 ;
	args[3] = arg3 ;
	args[4] = arg4;
	__bpf_trace_run(prog, args);
} [...]

Meaning, the EVALx() macros could be removed from there, too. Potentially, the
REPEAT() macro could sit in its own include/linux/ header for others to reuse
or such.

And people think my macro magic in include/trace/ftrace_event.h is
funky. Now I know who stole my MACRO MAGIC HAT.

-- Steve