Friday, February 8, 2013

Hooked on DTrace

Mark Dalrymple:

A friend of mine got an app rejected from the Mac AppStore because his app was (supposedly) attempting to open the Info.plist in DiskArbitration.framework in read/write mode. An app really shouldn’t be trying to write to anything in a system framework. Sad thing is, his app wasn’t doing this, at least not explicitly. It just used the framework, including it in Xcode in the usual manner and then calling its API. The framework was being loaded by the usual app startup machinery. It was an unjust accusation, but there’s really no recourse, short of resubmitting the app and hoping it works.

Wouldn’t be nice if you could catch every open being done by a program, and see what access flags it’s passing? You could take this output and see “oh yeah, for some reason I’m opening this read/write” and do some debugging, or else have some evidence for “I don’t see any wrongdoing”. Sounds like a great application of DTrace.

Update (2013-02-17): Part 2.

Update (2013-02-21): Part 3, which focuses on Objective-C:

Whenever faced with “who creates this” or “who calls this”, and I have no idea where to begin looking in the code, I reach for DTrace.

Update (2013-03-14): Part 4:

One way to do it is to make your own static probes. These are functions you explicitly call inside your program or library that tell DTrace “Hey, if you’re interested in country-clicking, someone just clicked on FI.” You can then put a DTrace probe on country-clicks, and all the other data available in DTrace is at your disposal like stack traces and timestamps.

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