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Systemtap vs DTrace – Safety?
By David Stewart (Intel) (94 posts) on June 27, 2008 at 2:15 am
(I'm attending the OpenSolaris Developer Conference, OSdevCon in Prague this week. Periodically I will try to live blog where I can about some of the talks I hear.)
I gave my keynote this morning to kick off the last day of the conference. Now that I can relax a little, I'm listening to a couple of talks on DTrace.
One comment I heard from the current speaker is that SystemTap in Linux works by compiling a script into C code, compiling the C code and then linking it into the kernel.
This is in contrast to DTrace, which takes the script written in the "D" language into an intermediate code (DIF) which is then interpreted by the in-kernel DIF virtual machine.
So, the SystemTap method seems really … um … unsafe. Particularly if you are linking into a running production system to trace it.
Now I suppose you can do Really Bad Things in DTrace as well. So maybe this is a difference without a distinction. (I was just told that there is a "allow destructive behavior" option in the DTrace implementation which is off by default.) Is a virtual machine interpreter any safer than generated C code?
Does anyone have experience with both, who can comment?
Categories: Open Source
Comments (5) 
By Frank Ch. Eigler on June 27th, 2008 at 5:14 am
> Is a virtual machine interpreter any safer than generated C code?
In practice, it does not appear so. To my knowledge, systemtap users
have experienced no safety-related problems caused by this specific aspect.
See also http://web.elastic.org/~fche/blog2/archive/2007/08/03/systemtap_safety
By Shawn Walker on June 27th, 2008 at 11:19 am
Bryan Cantrill believes that the DTrace approach is the safer one:
http://blogs.sun.com/bmc/entry/dtrace_safety
By Dave Stewart on June 29th, 2008 at 11:24 am
An interesting discussion. I certainly have heard the comment that "systemtap is not done yet" and it probably offers good opportunities to improve. Are there stories of people using systemtap on production, running systems to find out what's going on and fix it?
By Frank Ch. Eigler on June 30th, 2008 at 3:36 am
"Are there stories of people using systemtap on production"
Of course there are, and indeed we are not done yet. As I
said, problems that we encounter are for reasons other than
the compilation-to-C tactic, so referring to that as a potential
safety matter is merely speculative.
By ponies.homelinux.org » Safety on June 30th, 2008 at 7:09 pm
According to the EU Press Room, "As of today, aviation relations between the European Community and the United States will be further strengthened through an agreement on aviation safety. Thanks to the mutual recognition of aviation ...Comment on Systemtap vs DTrace ? Safety? by Frank Ch. EiglerOf course there are, and indeed we are not done yet. As I said, problems that we encounter are for reasons other than the compilation-to-C tactic, so referring to that as a potential safety matter is merely speculative.