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Re: copy faults from user_string* functions
- From: Eric Wong <normalperson at yhbt dot net>
- To: "Frank Ch. Eigler" <fche at redhat dot com>
- Cc: Systemtap List <systemtap at sourceware dot org>
- Date: Fri, 26 Jul 2013 17:56:02 +0000
- Subject: Re: copy faults from user_string* functions
- References: <20130726063634 dot GA32443 at dcvr dot yhbt dot net> <y0miozxmeqe dot fsf at fche dot csb>
"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