tenderlove / fisk Goto Github PK

I'm trying to encode the REP instruction, e.g. rep movsb, which, as far as I know, it's a valid x64 instruction.

I've checked the instructions list, but oddly, it's entirely missing, so I'm not sure if this is intentional.

I've written a lot of ruby (>15 years ago) but I've never dealt with building gems... (until now... my first attempt was for fisk). Tried to install fisk but ran into issues, as I did not get the gemspec right and the it did not get installed right. (was able to install all the prerequisites, include capstone dev, etc).

I modified the example so that it should work on Linux, but was not able to try it out...

Fisk would be perfect for a proof of concept prototype new language compiler I'm working on...

I think you need to do register allocation at the control-flow level, not the lexical instruction level.

For example your allocator will allocate this with just two registers, re-using r9 for both reg1 and reg3, but really reg1 is still alive.

reg1 = 1
reg2 = 1
head:
  goto break if reg1 > 100
  reg1 = reg1 + reg2
  reg3 = 1            # your register allocator thinks reg1 is dead at
                      # this point, so shares a register with reg3, but
                      # it's still alive - it's going to be used in the
                      # next iteration!
  reg2 = reg3
  goto head
break:

reg1 = fisk.register
fisk.mov reg1, fisk.imm32(1)
reg2 = fisk.register
fisk.mov reg2, fisk.imm32(1)
fisk.put_label(:head)
fisk.cmp reg1, fisk.imm32(100)
fisk.jg(fisk.label(:break))
fisk.add reg1, reg2
reg3 = fisk.register
fisk.mov reg3, fisk.imm32(1)
fisk.mov reg2, reg3
fisk.jmp(fisk.label(:head))
fisk.put_label(:break)
fisk.assign_registers([Fisk::Registers::R9, Fisk::Registers::R10])     # should fail!

I think instructions like set can only use the 8-bit registers, like sete al. I don't think Fisk provides access to these? Could it? I'm trying to reduce branches in https://github.com/kddnewton/regular_expression using set and cmov.

@kddnewton