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    SubjectRe: [PATCH -tip 10/10] perf probe: Accessing members in data structures
    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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