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

[Eric Blake <eblake@redhat.com>]

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.

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):
> +            raise ValueError("Event format must not contain field width '%*'")
>   
>           if len(fmt_trans) > 0:
>               fmt = [fmt_trans, fmt]
> 

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