DxBorks

To execute your own program, edit the program's memory in DxBorks/kernel/arch/i386/vm/vm.c. Example programs can be found below.

• The executed instruction is located at the address (%ip). The value C is the value located at the address (%ip) + 1.

• There are 4 registers, %a, %b, %c, and %d

• %ip is the instruction pointer

• %sp is the stack pointer, pointing to the top of the stack

• Every instruction takes 1 cycle to complete.

• The stack grows downwards from the highest memory location

• The program is loaded at address 0

• The VM's memory is somewhere between 0 and 256 bytes large.

• Registers are 8 bits wide

  OPCODE MNEMONIC DESCRIPTION

  0x00 nop Does nothing and consumes a cycle 0x01 add %a += %b 0x02 sub %a -= %b 0x03 xor %a ^= %b 0x04 or %a |= %b 0x05 not %a = ~%a 0x06 and %a &= %b 0x07 lshift %a << %b 0x08 rshift %a >> %b 0x09 loada %a = C 0x0a loadb %b = C 0x0b loadc %c = C 0x0c loadd %d = C 0x0d push ++(%sp), mem[%sp] = C 0x0e pusha ++(%sp), mem[%sp] = %a 0x0f pushb ++(%sp), mem[%sp] = %b 0x10 pushc ++(%sp), mem[%sp] = %c 0x11 pushd ++(%sp), mem[%sp] = %d 0x12 popa a = mem[%sp], --(%sp) 0x13 popb b = mem[%sp], --(%sp) 0x14 popc c = mem[%sp], --(%sp) 0x15 popd d = mem[%sp], --(%sp) 0x16 jmp %ip = C 0x17 cjmp if (flag) %ip = C 0x18 stop stops execution 0x19 eq flag = (%a == %b ? 1 : 0) 0x19 neq flag = (%a != %b ? 1 : 0) 0x19 less flag = (%a <= %b ? 1 : 0) 0x19 great flag = (%a >= %b ? 1 : 0) 0x1a inc ++(%a) 0x1e dec --(%a) 0x22 disp print(mem[C])

  Special instructions:

  0x-- exp %a = exp(%a) 0x-- log %a = log(%a) 0x-- mul %a *= %b 0x-- div %a /= %b 0x-- mod %a %= %b

Example programs

This program loads 22 in %a, 16 in %b, computes the sum of %a + %b, substracts 10, and doubles its value before storing it at the stop of the stack:

push 22       # Stores 22 on top of the stack
push 16       # Stores 16 on top of the stack
popb          # Pops the top of the stack (16) to %b
popa          # Pops the top of the stack (22) to %a
add           # Adds %b (16) to %a (22)
loadb 10      # Sets %b (16) to 10
sub           # Subtracts %b (10) from %a (38)
pusha         # Stores %a (38) on top of the stack
popb          # Pops the top of the stack (38) to %b (10)
add           # Adds %b (38) to %a (38)
pusha         # Stores %a (76) on top of the stack

When translated to hexadecimal VM code, we get:

0x0d 0x16
0x0d 0x10
0x13
0x12
0x01
0x0a 0x0a
0x02
0x0e
0x13
0x01
0x0e

Our program, when inlined, should be:

0x0d 0x16 0x0d 0x10 0x13 0x12 0x01 0x0a 0x0a 0x02 0x0e 0x13 0x01 0x0e

And should store 0x4C at the memory address (VM_MEM_SIZE-1) (default: 0xFF)