This is the mail archive of the
systemtap@sourceware.org
mailing list for the systemtap project.
Re: probes that access userspace
- From: "Frank Ch. Eigler" <fche at redhat dot com>
- To: Kevin Stafford <kevinrs at us dot ibm dot com>
- Cc: systemtap at sources dot redhat dot com
- Date: Fri, 14 Oct 2005 15:20:57 -0400
- Subject: Re: probes that access userspace
- References: <E55D.2090005__29732.3145241991$1129302467$gmane$org@us.ibm.com> <y0mzmpc2hkt.fsf@tooth.toronto.redhat.com> <435002D3.1050703@us.ibm.com>
Hi -
On Fri, Oct 14, 2005 at 12:11:15PM -0700, Kevin Stafford wrote:
> >>[...] If this is not possible, I think it would be useful to
> >>enhance the language such that a probe script could explicitly
> >>notify the translator of a user space pointer access [...]
> >>
> >Perhaps. Other than the system call interfaces, is this difficulty
> >likely to arise often elsewhere?
> >
> >[...] For user-level probes, there is no ambiguity: every
> >pointer dereference is in user space.
>
> Being that for user-level probes, every pointer dereference is in
> user space, I believe it is certain that this difficulty will arise
> elsewhere.
Perhaps I was being unclear. The "difficulty" I was referring to was
the ambiguity in whether an ordinary or special dereference operation
is required for any given $var->field expression. It is this
ambiguity that could be resolved by the user via a language extension,
and it is this ambiguity that does not exist for variables that show
up in user-level probes.
- FChE