[lttng-dev] [RFC] [PATCH] -Werror=old-style-definition and UST tracepoints

Hollis Blanchard hollis_blanchard at mentor.com
Fri Jun 8 14:26:23 EDT 2012

I've defined a tracepoint without arguments:







When I build (with -Werror=old-style-definition), I get this error:

    In file included from /home/hollisb/work/qemu.git/exec.c:59:0:

    /home/hollisb/work/qemu.git/tracepoints.h:24:2: error: function declaration isn’t a prototype [-Werror=strict-prototypes]

    /home/hollisb/work/qemu.git/tracepoints.h: In function ‘__tracepoint_cb_qemu_tb_hash___flushall’:

    /home/hollisb/work/qemu.git/tracepoints.h:24:2: error: old-style function definition [-Werror=old-style-definition]

    cc1: all warnings being treated as errors

The preprocessed code looks like so:

    extern struct

    # 129 "/usr/local/include/lttng/tracepoint.h" 3


    # 24 "/home/hollisb/work/qemu.git/tracepoints.h"


    # 19 "/home/hollisb/work/qemu.git/tracepoints.h"

      ; static __attribute__ (( always_inline )) __inline__ void


    # 19 "/home/hollisb/work/qemu.git/tracepoints.h"

      () { struct tracepoint_probe *__tp_probe; if (!tracepoint_dlopen.rcu_read_lock_sym_bp) return; tracepoint_dlopen.rcu_read_lock_sym_bp(); __tp_probe = ({ typeof(__tracepoint_qemu_tb_hash___flushall.probes) _________p1 = ((typeof(__tracepoint_qemu_tb_hash___flushall.probes)) (tracepoint_dlopen.rcu_dereference_sym_bp(((void *) (__tracepoint_qemu_tb_hash___flushall.probes))))); (_________p1); }); if (__builtin_expect(!!(!__tp_probe), 0)) goto end; do { void *__tp_cb = __tp_probe->func; void *__tp_data = __tp_probe->data; ((void (*)(void *__tp_data)) (__tp_cb)) (__tp_data); } while ((++__tp_probe)->func); end: tracepoint_dlopen.rcu_read_unlock_sym_bp(); } static __attribute__ (( always_inline )) __inline__ void

I believe the problem comes from -Werror=old-style-definition not liking 
that empty "()", i.e. tracepoint_cb_qemu_tb_hash___flushall() { ... }. 
The following patch seems to work for me; is there a reason it isn't 
already written this way?

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h

index 4b773bb..60d8c73 100644

--- a/include/lttng/tracepoint.h

+++ b/include/lttng/tracepoint.h

@@ -88,7 +88,7 @@ extern "C" {

  #define _TP_EXDATA_VAR20(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t)      __tp_data,b,d,f,h,j,l,n,p,r,t


  /* _TP_EXPROTO* extract tuples of type, var */

-#define _TP_EXPROTO0()

+#define _TP_EXPROTO0()                                         void

  #define _TP_EXPROTO2(a,b)                                      a b

  #define _TP_EXPROTO4(a,b,c,d)                                  a b,c d

  #define _TP_EXPROTO6(a,b,c,d,e,f)                              a b,c d,e f

If this is OK, I'm happy to resend as a proper patch.

Hollis Blanchard
Mentor Graphics, Embedded Systems Division

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