[ltt-dev] SystemTAP support in tracepoints

Josh Stone jistone at redhat.com
Mon Apr 11 18:29:41 EDT 2011

On 04/11/2011 02:19 PM, Josh Stone wrote:
> AFAIK, the only roadblock is that our probes are argument-numbered
> rather than variadic.  I've been thinking for a while that it would be
> nice if we had a variadic SDT macro, e.g. STAP_PROBEV, and then UST
> could invoke it directly.  Since you and I were brainstorming this,
> here's a neat trick I found to count __VA_ARGS__:
>   http://groups.google.com/group/comp.std.c/msg/346fc464319b1ee5
> I'm going to try to adapt that for SDT, so I'll post if I get it working...

Here's what I came up with:

#define _SDT_NARG(...) __SDT_NARG(__VA_ARGS__, 10,9,8,7,6,5,4,3,2,1,0)
#define __SDT_NARG(_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10, N, ...) N
#define _SDT_PROBE_N(provider, name, N, ...) \
  _SDT_PROBE(provider, name, N, (__VA_ARGS__))
#define STAP_PROBEV(provider, name, ...) \
  _SDT_PROBE_N(provider, name, _SDT_NARG(0,##__VA_ARGS__),##__VA_ARGS__)

_SDT_NARG is actually returning the count minus one, and I call it with
an extra arg, so we can avoid non-standard empty macro args.



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