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From: Jung-uk Kim <jkim@FreeBSD.org>
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Date: Tue, 16 Mar 2010 12:38:20 -0400
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Cc: Kostik Belousov <kostikbel@gmail.com>, Marcel Moolenaar <xcllnt@mac.com>
Subject: Re: [RFC] DTrace SYSCALL provider (was Re: [RFC] Saving the latest
	errno from syscalls.)
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On Monday 15 March 2010 02:10 pm, Jung-uk Kim wrote:
> On Friday 12 March 2010 01:32 pm, Jung-uk Kim wrote:
> > On Friday 12 March 2010 04:29 am, Kostik Belousov wrote:
> > > On Thu, Mar 11, 2010 at 06:15:07PM -0500, Jung-uk Kim wrote:
> > > > On Thursday 11 March 2010 04:55 pm, Marcel Moolenaar wrote:
> > > > > On Mar 11, 2010, at 1:24 PM, Jung-uk Kim wrote:
> > > > > > While I was debugging syscalls, I found a very useful
> > > > > > field in struct thread, td_errno.  It seems it was added
> > > > > > for dtrace but it is only populated on amd64 and i386. 
> > > > > > Is the attached patch acceptable for maintainers of other
> > > > > > platforms?
> > > > >
> > > > > Isn't it better to do it in cpu_set_syscall_retval()?
> > > > > That way you catch all cases, plus you can save the
> > > > > translated error as well...
> > > >
> > > > I just took amd64/i386 as an example and I was not sure
> > > > whether it was meant to store translated error or not.  Does
> > > > anyone with DTrace internal knowledge answer the question?
> > >
> > > I do not know that much about DTrace, but it seems that setting
> > > td_errno in cpu_set_syscall_retval() is too late. Dtrace has a
> > > probe after the syscall return, and it is called right before
> > > cpu_set_syscall_retval() can be reasonably called. The probe
> > > only issued for syscall that goes into sysent.
> >
> > Ah, I can see that now.  So, if/when we implement DTrace SYSCALL
> > provider for other arches, this is the right place. :-)
>
> I went ahead and implemented DTrace SYSCALL providers for non-x86
> arches.  It passes 'make universe' test but I don't know if it
> works. Can maintainers of other arches test or review the attached
> patch?

I realized there are too many missing pieces for DTrace to work on 
other arches. :-(

Please ignore this patch.

Jung-uk Kim