Messages in this thread | | | Date | Thu, 18 Mar 2010 04:28:07 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH -tip 10/10] perf probe: Accessing members in data structures |
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On Wed, Mar 17, 2010 at 03:14:43PM -0400, Masami Hiramatsu wrote: > Mark Wielaard wrote: > > On Tue, 2010-03-16 at 18:06 -0400, Masami Hiramatsu wrote: > >> Support accessing members in the data structures. With this, > >> perf-probe accepts data-structure members(IOW, it now accepts > >> dot '.' and arrow '->' operators) as probe arguemnts. > >> > >> e.g. > >> > >> ./perf probe --add 'schedule:44 rq->curr' > >> > >> ./perf probe --add 'vfs_read file->f_op->read file->f_path.dentry' > >> > >> Note that '>' can be interpreted as redirection in command-line. > > > > If you find that a problem then you can do like SystemTap does and allow > > '.' in place of '->'. In the code you already use the > > perf_probe_arg_field ref flag only to check that the DIE gives you the > > same information. So you could just drop that and use any separator. > > Then you decide based on whether you see a DW_TAG_pointer_type. This > > gives the user some extra flexibility by letting them not having to care > > about specifying extra type information already available elsewhere. > > Thanks, when designing this feature, I considered it too. > > Since perf probe already support displaying source code by --line option, > users will read the probed code itself and try to probe it. In that case, > I think they naturally use '.' and '->' as they read (they might try to > copy & paste it). > > So, I think that it would be good to support both of '.' and '->' as > they are used in the code, because it will not confuse users. > > Thank you,
Agreed.
And lets people use what is common for them: expressions that follow C rules in the context.
And those who will be more familiar with perf probe will know they can use the simplified "." based scheme.
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