[PATCH] tracetool: work around ust <sys/sdt.h> include conflict

[Stefan Hajnoczi <stefanha@redhat.com>]

Both the dtrace and ust backends may include <sys/sdt.h> but LTTng
Userspace Tracer 2.11 and later requires SDT_USE_VARIADIC to be defined
before including the header file.

This is a classic problem with C header files included from different
parts of a program. If the same header is included twice within the same
compilation unit then the first inclusion determines the macro
environment.

Work around this by defining SDT_USE_VARIADIC in the dtrace backend too.
It doesn't hurt and fixes a missing STAP_PROBEV() compiler error when
the ust backend is enabled together with the dtrace backend.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
I am also sending a fix to the LTTng Userspace Tracer project to add
-DSDT_USE_VARIADIC to the pkg-config CFLAGS so that applications define
the macro consistently. But this patch is still needed as a workaround
for lttng-ust 2.11.
---
 scripts/tracetool/backend/dtrace.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/tracetool/backend/dtrace.py b/scripts/tracetool/backend/dtrace.py
index 638990db79..79dbc2fa27 100644
--- a/scripts/tracetool/backend/dtrace.py
+++ b/scripts/tracetool/backend/dtrace.py
@@ -40,6 +40,12 @@ def generate_h_begin(events, group):
     else:
         header = "trace-dtrace.h"
 
+    # Workaround for ust backend, which also includes <sys/sdt.h> and may
+    # require SDT_USE_VARIADIC to be defined. If dtrace includes <sys/sdt.h>
+    # first without defining SDT_USE_VARIADIC then ust breaks because the
+    # STAP_PROBEV() macro is not defined.
+    out('#define SDT_USE_VARIADIC 1')
+
     out('#include "%s"' % header,
         '')
 
-- 
2.26.2