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Date: Tue, 19 May 2009 16:49:47 -0400
From: Wesley Shields <wxs@FreeBSD.org>
To: Thomas Backman <serenity@exscape.org>
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User-Agent: Mutt/1.5.19 (2009-01-05)
Cc: freebsd-current@freebsd.org
Subject: Re: DTrace panic while probing syscall::open (and possibly many
	others)
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On Mon, May 18, 2009 at 06:18:38PM +0200, Thomas Backman wrote:
> 
> On May 18, 2009, at 06:11 PM, Wesley Shields wrote:
> 
> > On Wed, May 13, 2009 at 03:19:05PM +0200, Thomas Backman wrote:
> >> OK, so I first posted a thread on the forums about this in 7.2- 
> >> RELEASE:
> >> http://forums.freebsd.org/showthread.php?t=3834
> >> Then filed a PR, kern/134408:
> >> http://www.freebsd.org/cgi/query-pr.cgi?pr=134408
> >>
> >> The very same bug remains in 8-CURRENT/amd64 as of May 13, ~10(am)
> >> GMT+2.
> >>
> >> Steps to reproduce:
> >> 1) Build DTrace capable kernel (I followed the wiki DTrace  
> >> instructions)
> >> 2) Reboot; kldload dtraceall
> >> 3) dtrace -n 'syscall::open:entry { self->path = arg0; }
> >> syscall::open:return { printf("%s\n", copyinstr(self->path)); }'
> >> 4) Crash.

I just noticed this but shouldn't you be using copyinstr() on the first
probe. It should look something like this:

syscall::open:entry
{
		self->path = copyinstr(arg0);
}

syscall::open:return
/ self->path /
{
		printf("%s\n", self->path);
}

This still doesn't solve the problem of copyinstr() causing a crash
though.

> >> Backtrace:
> >> [...]
> >
> > It's not the probe that is the problem. I suspect it's the copyinstr.
> >
> >> Same panic on two computers (a "real" one, A64 3200+, nForce4, 2GB  
> >> RAM;
> >> and a Macbook Pro C2D running VMware Fusion). Same panic in 7.2 and  
> >> 8.0.
> >
> > I can easily reproduce this also.
> >
> > -- WXS
> 
> Yup, it's copyinstr() crashing. It works if you simply replace  
> printf(...) with printf("file opened\n") which doesn't copy anything  
> in, and the backtrace seems (even to me ;) to point towards it.

Did this ever work? If so, can you do a binary search to help narrow
down when it broke?

-- WXS