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Date: Fri, 26 Jul 2013 17:56:00 -0000
From: Eric Wong <normalperson@yhbt.net>
To: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Systemtap List <systemtap@sourceware.org>
Subject: Re: copy faults from user_string* functions
Message-ID: <20130726175602.GA5773@dcvr.yhbt.net>
References: <20130726063634.GA32443@dcvr.yhbt.net> <y0miozxmeqe.fsf@fche.csb>
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"Frank Ch. Eigler" <fche@redhat.com> wrote:
> normalperson wrote:
> > Hi all, just to clarify, not all of these faults are user errors, right?
> > I get these sometimes with some strings (constants, I think):
> > ERROR: user string copy fault -14 at 000000000042f16c near identifier 'user_string_n' at $prefix/share/systemtap/tapset/uconversions.stp:120:10
> > [...]
> 
> It can simply mean having some not-yet-paged-in data, which in the
> spirit of non-interference, stap will not trigger a page fault for.
> Please try error-catching constructs such as try{}catch{}, or
> --skip-badvars to tolerate them.

Hi Frank, thanks for the response.  --skip-badvars seems to work for me.
Is there any optional way to get stap to trigger page faults to get
that data?

When tracing, losing a little performance is OK, especially with
cmogstored (which is entirely network/disk bound).

> > This is for cmogstored, if anybody is interested in reproducing this,
> > I've pushed my work-in-progress to the "st-wip-broken" branch of
> > git://bogomips.org/cmogstored.git   The HACKING doc in the top-level
> > should document all the build-dependencies if you want to try to
> > reproduce it.
> 
> Neat.
> 
> - FChE

-- 
Eric Wong