While bears a significant resemblance, Ertl and Gregg's approach is not automatic and every additional architecture requires a significant understanding of the target architecture---including an ability to ensure that fully relocable code can be generated and extracted. In comparison, the copy-and-patch approach can be thought as a simple dynamic linker, and objects generated by unmodified C compilers are far more predictable and need much less architecture-specific information for linking.
Does Ertl and Gregg's approach have any "upsides" over copy-and-patch? Or is it a case of just missing those one or two insights (or technologies) that make the whole thing a lot simpler to implement?
I think so, but I can't say this any more confident until I get an actual copy of their paper (I used other review papers to get the main idea instead).
The copy-and-patch also assumes the compiler will generate patchable code. For example, on some architecture, have a zero operand might have a smaller or different opcode compared to a more general operand. Same issue for relative jumps or offset ranges. It seems the main difference is that the patch approach also patches jumps to absolute addresses instead of requiring instruction-counter relative code.
