foo.c:
    #include "sdt.h"
    foo(size_t len)
    {
        ...; if (FOO_ENABLED()) { FOO(len) }; ...
    }

sdt.d:
    provider barsdt
    {
        probe foo(size_t len);
    }

sdt.h.do:
    redo-ifchange sdt.d conf/cmd/dtrace dtrace-dummy.pl
    read DTRACE < conf/cmd/dtrace
    [ -n "$DTRACE" ] || { ./dtrace-dummy.pl < sdt.d ; exit }
    $DTRACE -h -o $3 -s sdt.d