Metacompiler overhaul

[larsbrinkhoff]

The metacompiler is due for an overhaul.

• The current implementation is closely tied to building the kernel.

  • The kernel-specific code should be split off.
  • The compiler should be made a generic cross compiler.

• Everything is written to a single memory space.

  • Many microcontrollers use a Harvard architecture and need separate code and data spaces.
  • Some applications may want to have separate read-only and read-write data spaces.
  • The word headers can be written to a separate area.

• Building and saving the image is constrained by the single memory space.

  • Must write everything sequentially from start to end.
  • It would be better to be able to write many separate sections and assemble them together in the end.

[pipcet]

The asm.js target essentially has separate code and data spaces; it gets around the single memory space limitation by compiling to the data space and emitting code directly. The wasm target also has separate code and data spaces, and makes two passes over the nucleus, one for the code and one for the data (it would require a third pass to actually just count the number of defined words, but right now that's hardcoded). So these two targets would benefit a lot from this improvement.

gas has sections and numbered subsections within those. That's sufficient for WebAssembly, while simple sections might not be.

[larsbrinkhoff]

• Splitting off code into separate files was a great success

  • Hide complexity in self-contained components.
  • Avoid dependencies.
  • Do more of that?

• Support for relocation?

  • GEMDOS executables really need this.
  • Also usable for the C target.