[qemu-xen staging] tracetool: work around ust <sys/sdt.h> include conflict

[patchbot@xxxxxxx]

commit 27e08bab94f7c6ebe0b75938c98c394c969e3fd8
Author:     Stefan Hajnoczi <stefanha@xxxxxxxxxx>
AuthorDate: Thu Jun 25 15:07:57 2020 +0100
Commit:     Stefan Hajnoczi <stefanha@xxxxxxxxxx>
CommitDate: Tue Jul 7 16:07:14 2020 +0100

    tracetool: work around ust <sys/sdt.h> include conflict
    
    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@xxxxxxxxxx>
    Message-id: 20200625140757.237012-1-stefanha@xxxxxxxxxx
    Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
 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 5711892ba0..b7fe4c1b50 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,
         '')
 
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