cowboy8625/bitbox

right now just a vm

Bitbox

Bitbox is currently just a register based virtual machine. The goal of the project is to have a target IR (intermediate representation) to compile your language to and then provide you with a VM and a way to target native code.

Header

offset	size	purpose
0x00	4	0x42, 0x42, 0x4f, 0x58 in ASCII these four bytes constitute the magic number.
0x04	4	How big the .data section is
0x08	4	Entry point into .text section
0x0C	52	Not used section

Insturctions Supported

Instructions consist of a 3 main parts.

1. Code: this is one byte
2. Type: this is one byte

• if type is 0b1000_0000 then type is signed integer
• if type is 0x00 then there are no args

3. Args: this is one byte to as many bytes as needed

• Arg 1: this is one byte
• Arg 2: this is two bytes
• Arg 3: this is three bytes
• Arg 1 with Immediate Value: this is one to as many bytes as needed. The type will dictate the size.

Note: opcode numbers may not be correct as they can change as we add more instructions

instruction	opcode	type	data
✅ load	0		Reg,Imm
✅ store	1		Reg,Reg
✅ copy	2		Reg,Reg
✅ aloc	3		Reg,Reg
✅ push	4		Reg
✅ pop	5		Reg
✅ add	6		Reg,Reg,Reg
✅ sub	7		Reg,Reg,Reg
✅ div	8		Reg,Reg,Reg
✅ mul	9		Reg,Reg,Reg
✅ inc	10		Reg
✅ eq	11		Reg,Reg
✅ jne	12		Reg,Reg,Label
✅ hult	13
✅ printreg	14		Reg
✅ call	15		Label
✅ and	16		Reg,Reg,Reg
✅ or	17		Reg,Reg,Reg
✅ shr	18		Reg,Reg,Reg
✅ return	19
✅ syscall	20
🟥 jmp	N/A		Label
🟥 jeq	N/A		Label
🟥 nop	N/A
🟥 ige	N/A
🟥 not	N/A		Reg
🟥 xor	N/A		Reg,Reg,Reg
🟥 shl	N/A		Reg,Reg,Reg
🟥 sar	N/A		Reg,Reg,Reg
🟥 rol	N/A		Reg,Reg,Reg
🟥 ror	N/A		Reg,Reg,Reg
🟥 neq	N/A		Reg,Reg
🟥 gt	N/A		Reg,Reg
🟥 geq	N/A		Reg,Reg
🟥 lt	N/A		Reg,Reg
🟥 leq	N/A		Reg,Reg
🟥 dec	N/A		Reg

Syscall

Register 0 is used for the syscall number, register 1-4 are used for arguments.

name	reg 0	reg 1	reg 2	reg 3	reg 4
WRITE	0	ptr to string	string length	static string	N/A

Command Line Arguments

The command line arguments are placed in the heap. Each argument pointer will be place on the stack. Pointers will have the string length on the upper half of the pointer. Register 0 will be set to the number of arguments.

Example

Print all arguments given to program

.entry main
main:
    copy[u64] %31 %0 ; args length
    load[u64] %30 0  ; count
    load[u64] %0  1  ; length of string
    aloc[u64] %29 %0
    load[u8] %0  0xA  ; char `\n`
    store[u8] %29 %0

loop:
    ; get the ptr to string and length
    pop[u64] %5

    ; get ptr
    load[u64] %1 0b1111_1111_1111_1111_1111_1111_1111_1111
    and[u64] %1 %1 %5

    ; get length
    load[u64] %6 32
    shr[u64] %2 %5 %6 ; shift right by 32 bits

    ; write first arg
    load[u8] %0 0
    ; %1 ptr
    ; %2 length
    load[u8] %3 0
    syscall

    copy[u64] %1 %29 ; ptr
    load[u64] %2 1   ; length
    syscall

    inc[u64] %30
    jne %31 %30 loop

    hult