Universal Procedure Pointers
A UPP was a simple data structure that described the calling conventions and location of a PowerPC function in RAM, and started with a 68000 instruction. This data structure could be handed to any system function where it expected a callback, and could be executed by 68000 code just like a function pointer.
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But of course the Intel CPU didn’t have that [endian] switch. And since an emulator only knows about raw bytes, the PowerPC emulator (“Rosetta”) in Intel Macs could not transparently convert the stored bytes. So it was decided to not allow mixing of PowerPC or Intel code at all. There would only be a tiny bit of translation at the point when a PowerPC application called into the system.
