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Is this any different from detecting illegal instructions in general?

I would have thought any encoding in the unused part of the instruction space would generate a SIGILL, needing the "we don't do that here" logic.

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A bit fuzzy. I mostly work on M-class so idk what the sig would be, but a cursory glance says there's a dedicated "go to Jazelle" instruction that maybe it deals with differently? That way if any bytecodes overlap with arm/thumb it'll still know. Thinking about it, I'm more certain that's what it is. Maybe there's a bytecode that's a valid non-Java encoding that's a valid instruction, so they focus on the Jazelle mode entry

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