Tips for implementing x86_64 support

[Omay238]

I'm going to attempt to make x86_64, so how would people suggest I do this? Any useful resources?

[copy]

Heads-up: This is probably a 3-6 month project (full-time).

The Intel software developer's manual is the main reference: https://cdrdv2.intel.com/v1/dl/getContent/671200
wiki.osdev.org is sometimes useful, e.g. https://wiki.osdev.org/Paging

I'd suggest starting with disabling the jit, because that's a complex project by itself.

Breaking it down:

• Add support for switching to long mode
• Extend the instruction decoder generator (gen/generate_interpreter.js), note that some regular instructions (e.g. the brilliant single-byte inc esp instruction) become prefixes
• Add support for 64-bit paging (see Add support for PAE (#97) #599 for an example of adding a new paging mode)
  • Probably requires adding support for NX pages, i.e. memory access from eip need an extra check
• Make register 64 bits wide (existing instructions might need to special care; for example, mov eax, ebx clears the upper bits of rax)
• Make 64-bit variants of all instructions