Discussion Over Apple's Modification Of Sun's DTrace
One of the most anticipated features of Mac OS X Leopard amongst the technical community was the port of Sun's DTrace utility for application and system profiling. DTrace is a powerful, low-level dynamic tracing framework that allows system administrators and developers to trace applications for tuning or troubleshooting purposes.
Recently, Adam Leventhal, one of DTrace's initial developers, discovered that Apple's implementation creates a way for a program to exclude itself from being traced. Namely, he was unsuccessful at tracing iTunes, and found that Apple had added a method of disabling probing on certain applications defined with the directive P_LNOATTACH.
Since the initial publication of the blog entry last week, the story has begun to pop up around the mac web.
The practice is not entirely new to Apple. A commenter on Adam Leventhal's blog noted that Apple used the same directive to prevent GDB tracing on iTunes. Additionally, the implementation of this directive appears to be limited to iTunes (for the moment?), so many are speculating that the move is to protect Apple's FairPlay DRM.
To present an alternate view, Apple has extended Java, Ruby, Python, and Perl to include DTrace support, and Apple has built a GUI front-end called Instruments. Also the issue may eventually become moot with Apple's stated desire to move towards DRM-free music (though DRM video remains common).
Recently, Adam Leventhal, one of DTrace's initial developers, discovered that Apple's implementation creates a way for a program to exclude itself from being traced. Namely, he was unsuccessful at tracing iTunes, and found that Apple had added a method of disabling probing on certain applications defined with the directive P_LNOATTACH.
Wow. So Apple is explicitly preventing DTrace from examining or recording data for processes which don't permit tracing. This is antithetical to the notion of systemic tracing, antithetical to the goals of DTrace, and antithetical to the spirit of open source. I'm sure this was inserted under pressure from ISVs, but that makes the pill no easier to swallow.
Since the initial publication of the blog entry last week, the story has begun to pop up around the mac web.
The practice is not entirely new to Apple. A commenter on Adam Leventhal's blog noted that Apple used the same directive to prevent GDB tracing on iTunes. Additionally, the implementation of this directive appears to be limited to iTunes (for the moment?), so many are speculating that the move is to protect Apple's FairPlay DRM.
To present an alternate view, Apple has extended Java, Ruby, Python, and Perl to include DTrace support, and Apple has built a GUI front-end called Instruments. Also the issue may eventually become moot with Apple's stated desire to move towards DRM-free music (though DRM video remains common).
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53 months ago
For those interested, from Adam's blog... the code that was added.
#if defined(__APPLE__)
/*
* If the thread on which this probe has fired belongs to a process marked P_LNOATTACH
* then this enabling is not permitted to observe it. Move along, nothing to see here.
*/
if (ISSET(current_proc()->p_lflag, P_LNOATTACH)) {
continue;
}
#endif /* __APPLE__ */
#if defined(__APPLE__)
/*
* If the thread on which this probe has fired belongs to a process marked P_LNOATTACH
* then this enabling is not permitted to observe it. Move along, nothing to see here.
*/
if (ISSET(current_proc()->p_lflag, P_LNOATTACH)) {
continue;
}
#endif /* __APPLE__ */
53 months ago
...the point Apple was trying to make here. Preventing iTunes from being traced when there exist things like QTFairUse which rid the DRM in Apple sold music and continue to support latest iTunes versions.
On top of that, noted developer Landon Fuller posted a fairly quick and tiny Kext with source that will disallow applications from doing the NOATTACH trick so iTunes can be traced anyways.
:confused:
On top of that, noted developer Landon Fuller posted a fairly quick and tiny Kext with source that will disallow applications from doing the NOATTACH trick so iTunes can be traced anyways.
:confused:
53 months ago
And the reason it's so easy to see what's going on?
Because the source code for things like dtrace is readily available on Apple's site.
And since the source is available, it's easy to fix for things like gdb and dtrace.
Making good-faith attempts to protect things like iTunes is a necessary evil for Apple to play in things like the video rental realm. Some people might not like it, but for the current iTunes ecosystem to exist, it's simply necessary to take steps to make the DRM environment more difficult to defeat.
But since Jobs himself has stated in no uncertain terms that DRM will always be broken - both literally and figuratively - this simply represents a necessary intermediate step to a world where digital content isn't encumbered with DRM. And it's only Apple who is going to be able to move the industry in that direction the fastest, because they have the most influence. In the meantime, Apple needs to do what needs to be done.
If FairPlay was trivial (anymore trivial than it already has been, anyway) to break, do you think Apple would have been able to get ALL the studios on board for movie rentals?
That means Apple takes actions which can be construed to ISVs as good-faith attempts to protect FairPlay.
Because the source code for things like dtrace is readily available on Apple's site.
And since the source is available, it's easy to fix for things like gdb and dtrace.
Making good-faith attempts to protect things like iTunes is a necessary evil for Apple to play in things like the video rental realm. Some people might not like it, but for the current iTunes ecosystem to exist, it's simply necessary to take steps to make the DRM environment more difficult to defeat.
But since Jobs himself has stated in no uncertain terms that DRM will always be broken - both literally and figuratively - this simply represents a necessary intermediate step to a world where digital content isn't encumbered with DRM. And it's only Apple who is going to be able to move the industry in that direction the fastest, because they have the most influence. In the meantime, Apple needs to do what needs to be done.
If FairPlay was trivial (anymore trivial than it already has been, anyway) to break, do you think Apple would have been able to get ALL the studios on board for movie rentals?
That means Apple takes actions which can be construed to ISVs as good-faith attempts to protect FairPlay.
53 months ago
As a mac user for the past year and a half, all I have to say is...
....Wha? :confused:
....Wha? :confused:
53 months ago
Also the issue may eventually become moot with Apple's stated desire to move towards DRM-free music.
53 months ago
Music might be on its way to no-DRM, but FairPlay is also used for movies, so I don't see how the issue will be obviated - especially with the new movie rentals which need DRM by nature.
irmongoose
irmongoose
53 months ago
Apple only brought out their desire to sell DRM-free music after the music studios decided that was the way to go.
Steve Jobs happily changes his mind however it benefits him.
Steve Jobs happily changes his mind however it benefits him.
53 months ago
Why should an average user even care about this?
I'm not trying to be a jerk, I'm seriously wondering. If you're not a software developer, does this affect you? Why shouldn't Apple be able to protect a designated part of their code? They don't seem to have a problem opening up things besides iTunes.
I'm not trying to be a jerk, I'm seriously wondering. If you're not a software developer, does this affect you? Why shouldn't Apple be able to protect a designated part of their code? They don't seem to have a problem opening up things besides iTunes.
53 months ago
Apple only brought out their desire to sell DRM-free music after the music studios decided that was the way to go.
Steve Jobs happily changes his mind however it benefits him.
You are completely wrong, and that is revisionist history.
No one is staying Steve Jobs is God, but the DRM statement was the single biggest shot across the bow with respect to DRM that the music industry has EVER had from anyone close to that stature, and it was only AFTER that statement that the vast, vast, overwhelming majority of no-DRM music sales activity has gone on.
Was it due exclusively and only to Jobs? No.
Did it have a lot to do with that? Absolutely. Both from the standpoint of the statement, and from the standpoint of content owners trying to figure out how to still make content available to the widest range of customers without being beholden to iTunes.
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