Re: [PATCH v2 3/3] trace: Forbid dynamic field width in event format

[Eric Blake]

On 11/8/19 10:07 AM, Eric Blake wrote:
> On 11/8/19 8:40 AM, Philippe Mathieu-Daudé wrote:
> > 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:
>
> > +++ b/scripts/tracetool/__init__.py
> > @@ -206,6 +206,7 @@ class Event(object):
> >                         "\s*"
> >                         "(?:(?:(?P<fmt_trans>\".+),)?\s*(?P<fmt>\".+))?"
> >                         "\s*")
> > +    _DFWRE = re.compile(".*(%0?\*).*")
>
> The use of leading and trailing .* is pointless if the RE itself is used 
> unanchored and where you only care if the () matched.

Following up on this (based on an IRC conversation):

re.match _is_ anchored by default, while re.search is unanchored

> This doesn't catch all valid uses of * in a printf format.  Better might 
> be something like:
>
> _DFWRE = re.compile("%[\d\.\- +#']*\*")
>
> which matches only if there is a %, any number of characters that can 
> form a printf flag, as well as a numeric field width but dynamic precision.
>
>
> > +        if Event._DFWRE.match(fmt):

Or put differently, if you want to drop the .* from the compiled regex, 
then you need to use .search(fmt) here rather than .match(fmt).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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