scripts/tracetool: Fix dtrace generation for macOS

dtrace USDT is fully supported since OS X 10.6. There are a few
peculiarities compared to other dtrace flavors.

1. It doesn't accept empty files.
2. It doesn't recognize bool type but accepts C99 _Bool.
3. It converts int8_t * in probe points to char * in
   header files and introduces [-Wpointer-sign] warning.

Cc: Cameron Esfahani <dirty@apple.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20200717093517.73397-2-r.bolshakov@yadro.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/format/d.py

@@ -13,6 +13,7 @@
 
 
 from tracetool import out
+from sys import platform
 
 
 # Reserved keywords from
@@ -34,7 +35,8 @@ def generate(events, backend, group):
 
     # SystemTap's dtrace(1) warns about empty "provider qemu {}" but is happy
     # with an empty file.  Avoid the warning.
-    if not events:
+    # But dtrace on macOS can't deal with empty files.
+    if not events and platform != "darwin":
         return
 
     out('/* This file is autogenerated by tracetool, do not edit. */'
@@ -44,6 +46,17 @@ def generate(events, backend, group):
     for e in events:
         args = []
         for type_, name in e.args:
+            if platform == "darwin":
+                # macOS dtrace accepts only C99 _Bool
+                if type_ == 'bool':
+                    type_ = '_Bool'
+                if type_ == 'bool *':
+                    type_ = '_Bool *'
+                # It converts int8_t * in probe points to char * in header
+                # files and introduces [-Wpointer-sign] warning.
+                # Avoid it by changing probe type to signed char * beforehand.
+                if type_ == 'int8_t *':
+                    type_ = 'signed char *'
             if name in RESERVED_WORDS:
                 name += '_'
             args.append(type_ + ' ' + name)