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diff --git a/docs/history/04-darwin-compiler/notes.md b/docs/history/04-darwin-compiler/notes.md new file mode 100644 index 0000000..b42a9c8 --- /dev/null +++ b/docs/history/04-darwin-compiler/notes.md @@ -0,0 +1,9 @@ +# an ahead-of-time compiler to darwin arm64 + +no code from this stage survives except where a code/ folder sits next to this file. these are the notes as they were written in the transcript. + +## message 4 + +> now let's move in stages. write a compiler that takes this assembler's code and converts it into darwin arm + +**summary:** an ungolfed c89 compiler from vm assembly to darwin arm64 assembly. every word got its own label, the image was emitted as an addressable data array, x19/x20/x21 held the memory base and the two stack pointers, and computed jumps went through a table of offsets. a literal followed by a jump became a direct branch. `Q` and `G` went through `sxtb`, since char is signed on apple arm64, and `J` was read with `ldrb`. it was verified by assembling with llvm-mc for darwin, then rewriting to linux with sed and running under qemu, where it matched the vm byte for byte. this version couldn't handle self-modifying code. |