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Following legacy packing conventions, `isArm` was defined just for 32-bit ARM instruction set. This is confusing to non packagers though, because Aarch64 is an ARM instruction set. The official ARM overview for ARMv8[1] is surprisingly not confusing, given the overall state of affairs for ARM naming conventions, and offers us a solution. It divides the nomenclature into three levels: ``` ISA: ARMv8 {-A, -R, -M} / \ Mode: Aarch32 Aarch64 | / \ Encoding: A64 A32 T32 ``` At the top is the overall v8 instruction set archicture. Second are the two modes, defined by bitwidth but differing in other semantics too, and buttom are the encodings, (hopefully?) isomorphic if they encode the same mode. The 32 bit encodings are mostly backwards compatible with previous non-Thumb and Thumb encodings, and if so we can pun the mode names to instead mean "sets of compatable or isomorphic encodings", and then voilà we have nice names for 32-bit and 64-bit arm instruction sets which do not use the word ARM so as to not confused either laymen or experienced ARM packages. [1]: https://developer.arm.com/products/architecture/a-profile |
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