SymbOS: Graphical Z80 Multitasking Operating System

Post by jacquesm » Sat, Jan 06, 2018, 11:49 AM UTC

Sir_Cmpwn wrote: post #95

jacquesm wrote: post #88

Earlier quoted context omitted.

Wrote my own for 68xx and 65xx chips in ancient times. https://en.wikipedia.org/wiki/Relocation_(computing) If you have access to the symbol table it is an easy problem to solve, if you don't it can get quite difficult all the way to impossible if the original code makes use of tricks such as jumping into the middle of an instruction. But if the code is 'well behaved' then it can usually be done. Many games used tric…

For fun, I took a "happy medium" approach in KnightOS. Programs are written with RSTs (basically the z80 version of traps) next to each instruction with a relative address, then the kernel looks up the return address on the stack, partially decodes the next instruction, and then modifies the code in RAM to update the address to the correct one. It's basically just-in-time PIC. https://github.com/KnightOS/kernel/blob/…

Post by Sir_Cmpwn » Sat, Jan 06, 2018, 11:01 PM UTC

jacquesm wrote: post #101

Sir_Cmpwn wrote: post #95

Earlier quoted context omitted.

For fun, I took a "happy medium" approach in KnightOS. Programs are written with RSTs (basically the z80 version of traps) next to each instruction with a relative address, then the kernel looks up the return address on the stack, partially decodes the next instruction, and then modifies the code in RAM to update the address to the correct one. It's basically just-in-time PIC. https://github.com/KnightOS/kernel/blob/…

Heh, that's cool. How do you remember which ones you've modified so you don't do it twice?