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When `kIOHIDOptionsTypeSeizeDevice` is used in a DriverKit system extension (dext), the seized device fails to be hidden from `IOHIDManager` functions such as `IOHIDManagerSetDeviceMatchingMultiple`.
IMPORTANT
This is a modified, Markdown rich text version of my Radar bug report writeup to Apple (FB9785807).
I will not be posting or conveying any of Apple's responses, as I want to err on the side of caution and do not want to run the risk of accidentally posting what may be considered confidential information.
This is an excerpt from our internal documentation describing an issue with drawing in NSViews on macOS Big Sur.
1️⃣ Introduction
In macOS Big Sur (probably starting with β9), Apple changed the default contents format for backing layers of NSViews. Instead of an explicit CALayerContentsFormat.RGBA8Uint value, an „Automatic“ value is now used. Even though it also resolves into „RGBA8“ in our testing, it has some serious implications as it breaks assumptions our code relies on.
I first stumbled upon this issue in this tweet by Frank. It links to a thread on Apple Forums by Mark that contains valuable information as well as ideas for workarounds. The changed behavior was also confirmed by Marcin in this tweet.
What is the Strict Aliasing Rule and Why do we care?
(OR Type Punning, Undefined Behavior and Alignment, Oh My!)
What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.
In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.
Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th