Since not all trace backends support dynamic field width in
format (dtrace via stap does not), forbid them.

Add a check to refuse field width in new formats:

  $ make
  [...]
    GEN     hw/block/trace.h
  Traceback (most recent call last):
    File "scripts/tracetool.py", line 152, in <module>
      main(sys.argv)
    File "scripts/tracetool.py", line 143, in main
      events.extend(tracetool.read_events(fh, arg))
    File "scripts/tracetool/__init__.py", line 371, in read_events
      event = Event.build(line)
    File "scripts/tracetool/__init__.py", line 285, in build
      raise ValueError("Event format must not contain field width '%*'")
  ValueError: Error at hw/block/trace-events:11: Event format must not contain field width '%*'

Reported-by: Eric Blake <eblake@redhat.com>
Buglink: https://bugs.launchpad.net/qemu/+bug/1844817
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 scripts/tracetool/__init__.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
index 44c118bc2a..e239be602b 100644
--- a/scripts/tracetool/__init__.py
+++ b/scripts/tracetool/__init__.py
@@ -206,6 +206,7 @@ class Event(object):
                       "\s*"
                       "(?:(?:(?P<fmt_trans>\".+),)?\s*(?P<fmt>\".+))?"
                       "\s*")
+    _DFWRE = re.compile(".*(%0?\*).*")
 
     _VALID_PROPS = set(["disable", "tcg", "tcg-trans", "tcg-exec", "vcpu"])
 
@@ -280,6 +281,8 @@ class Event(object):
         if fmt.endswith(r'\n"'):
             raise ValueError("Event format must not end with a newline "
                              "character")
+        if Event._DFWRE.match(fmt):
+            raise ValueError("Event format must not contain field width '%*'")
 
         if len(fmt_trans) > 0:
             fmt = [fmt_trans, fmt]
-- 
2.21.0