[Qemu-devel] Build failure with trace-backend=ust

[Harsh Bora]

Hi,
I tried to explore LTTng UST with Qemu and built ust 0.15 (with urcu 
0.16 as reqd) and observed that Qemu gives compilation errors when built 
for trace-backend = ust. See this:

address@hidden v9fs]$ ./configure '--target-list=x86_64-softmmu' 
'--enable-debug' '--enable-kvm' --enable-trace-backend=ust
address@hidden v9fs]$ make
  GEN   x86_64-softmmu/config-devices.mak
  GEN   config-all-devices.mak
  GEN   qemu-options.texi

[.. snip ..]

  CC    qemu-option.o
  CC    cutils.o
  CC    osdep.o
In file included from osdep.c:49:
trace.h: In function ‘__trace_ust_slavio_misc_update_irq_raise’:
trace.h:277: error: ‘void’ must be the only parameter
trace.h:277: error: expected expression before ‘)’ token
trace.h:277: error: too many arguments to function ‘(void (*)(void 
*))__tp_it_func’
trace.h: At top level:
trace.h:277: error: ‘void’ must be the only parameter
trace.h:277: error: ‘void’ must be the only parameter
In file included from osdep.c:49:
trace.h: In function ‘__trace_ust_slavio_misc_update_irq_lower’:
trace.h:280: error: ‘void’ must be the only parameter
trace.h:280: error: expected expression before ‘)’ token
trace.h:280: error: too many arguments to function ‘(void (*)(void 
*))__tp_it_func’
trace.h: At top level:
trace.h:280: error: ‘void’ must be the only parameter
trace.h:280: error: ‘void’ must be the only parameter
In file included from osdep.c:49:
trace.h: In function ‘__trace_ust_slavio_timer_mem_writel_counter_invalid’:
trace.h:352: error: ‘void’ must be the only parameter
trace.h:352: error: expected expression before ‘)’ token
trace.h:352: error: too many arguments to function ‘(void (*)(void 
*))__tp_it_func’

[.. snip ..]

It appears that all trace-events with void parameter and a descriptive 
format string (in trace-events file) are thrown back with error. I 
explored LTTng's ust code and found that it also has a 
_DECLARE_TRACEPOINT_NOARGS to be used with events with no args (void 
arg). I see that in qemu we only use DECLARE_TRACE as in commit 
7e24e92a0615ee6be036743f2a035554d2ceac56. See below:

+linetoh_ust()
+{
+    local name args argnames
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1")
+
+    cat <<EOF
+DECLARE_TRACE(ust_$name, TPPROTO($args), TPARGS($argnames));
+#define trace_$name trace_ust_$name
+EOF

Do we need to put a check on args and if its void, use 
_DECLARE_TRACEPOINT_NOARGS instead ? Please enlighten.

regards,
Harsh