Hi Josh,
Following our discussion, I started to think about how we could be
support the systemtap breakpoint approach in UST tracepoints. I created
the following prototype that should let us handle a variable number of
arguments. The "args" I get here from the args... parameter would be
taken from the "TP_ARGS()" declaration in the TRACE_EVENT header. The
code below is really just to see if it is doable at all.
Comments are welcome,
Thanks,
Mathieu
#include <stdio.h>
#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
#define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
#undef offsetof
#ifdef __compiler_offsetof
#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
#else
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif
/* for x86 64 */
#define _ASM_PTR ".quad "
#define A(first, args...) \
"g" (first)
#define B(first, args...) \
"g" (first), A(args, 0)
#define C(first, args...) \
"g" (first), B(args, 0)
#define D(first, args...) \
"g" (first), C(args, 0)
#define E(first, args...) \
"g" (first), D(args, 0)
#define NARGS(args...) \
(sizeof(struct { unsigned char args; }) / sizeof(unsigned char))
#define _TRACE_GET_IP() \
".section __tracepoint_ip\"aw\"\n\t" \
_ASM_PTR "(1f)\n\t" \
".previous\n\t" \
"1:\n\t"
#define trace(name, args...) \
do { \
__builtin_choose_expr((NARGS(args) == 0), 0, 0); \
__builtin_choose_expr((NARGS(args) == 1), ({ asm volatile
(_TRACE_GET_IP() : : A(args, 0) : "memory"); 0; }), 0); \
__builtin_choose_expr((NARGS(args) == 2), ({ asm volatile
(_TRACE_GET_IP() : : B(args, 0) : "memory"); 0; }), 0); \
__builtin_choose_expr((NARGS(args) == 3), ({ asm volatile
(_TRACE_GET_IP() : : C(args, 0) : "memory"); 0; }), 0); \
__builtin_choose_expr((NARGS(args) == 4), ({ asm volatile
(_TRACE_GET_IP() : : D(args, 0) : "memory"); 0; }), 0); \
__builtin_choose_expr((NARGS(args) == 5), ({ asm volatile
(_TRACE_GET_IP() : : E(args, 0) : "memory"); 0; }), 0); \
BUILD_BUG_ON(NARGS(args) > 5); \
} while (0)
int main(int argc, char **argv)
{
int one, two, three, four;
unsigned long long five;
trace(name, one, two, three, four, five);
trace(name, one, two, three);
trace(name, one);
// error trace(name, one, two, three, four, five, six);
// error trace(name, one, two, three, four, noexist);
return 0;
}
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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