jaysmito101 / vermin_vm

A Virtual Machine + Assembler written in C

vermin_vm

A Virtual Machine + Assembler written in C

SPECS:

REGISTORS

Naming format: R* [ex: R0, R1, ..., R15]

Each registor is 64 bit in size

Accessing specific parts of registors:

Entire registor : R* [ex: R0, R1, ...]
Lower 32-bits : RLH [ex: R0LH, R1LH, ...]
Upper 32-bits : RUH [ex: R0UH, R1UH, ...]
Lower 16-bits of Lower 32-bit : RLQ [ex: R0LQ, R1LQ, ...]
Upper 16-bits of Lower 32-bit : RUQ [ex: R0UQ, R1UQ, ...]
Lower 8-bits of Lower 16-bit : RLT [ex: R0LT, R1LT, ...]
Upper 8-bits of Lower 16-bit : RUT [ex: R0UT, R1UT, ...]

Registor representation:

A registor is representated by a 32 bit integer:

Bits	Purpose
0 - 8	ID [0 - 15]
9 - 16	Size [64 (8), 32 (4), 16 (2), 8 (1)]
17 - 24	Lower / Upper part [Lower (0), Upper (1)]
25 - 32	Registor Local offset [8-bit integer]

Sepcial Registors:

Registers	Purpose
R15	Instruction pointer
R14	Stack start pointer
R13	Stack top pointer
R12	Heap start pointer
R8 to R11	Reserved

MEMORY LAYOUT

ADDRESS INCREASES DOWNWARDS
BEGIN
R14
STACK
R13
R12
HEAP
END

Assembly Instructions:

Each instruction has the following format:

[8-bit id][8-bit size in bytes][16-bit sub params] [32 x n-bit params]

NOTE: First 32 bits are compulsory

---

NOP

ID = 0

Size = 4

SubParams = NULL

---

MOV

ID = 1

Size = 4 + 2 * 4 [ = 12]

SubParams [first 8 bits] = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3), Reg to Reg Memory (4)

SubParams [second 8 bits] = size to move in bytes

Params = 2

Moves data from param 2 to param 1

---

ADD

ID = 2

Size = 4 + 2 * 4 [ = 12]

SubParams = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3)

Params = 2

Adds content of param 2 and 1 (1 + 2) and stores in 1

---

SUB/CMP

ID = 3

Size = 4 + 2 * 4 [ = 12]

SubParams = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3)

Params = 2

Subs content of param 2 and 1 (1 - 2) and stores in 1 and also in R8

---

MUL

ID = 4

Size = 4 + 2 * 4 [ = 12]

SubParams = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3)

Params = 2

Muls content of param 2 and 1 (1 * 2) and stores in 1

---

DIV

ID = 5

Size = 4 + 2 * 4 [ = 12]

SubParams = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3)

Params = 2

Divs content of param 2 and 1 (1 / 2) and stores Quotient 1 and remainder in R8

---

INC

ID = 6

Size = 4 + 4 [ = 8]

SubParams = NULL

Params = 1 [ a registor ]

Increments contents of registor by 1

---

DEC

ID = 7

Size = 4 + 4 [ = 8]

SubParams = NULL

Params = 1 [ a registor ]

Decrements contents of registor by 1

---

XOR

ID = 8

Size = 4 + 2 * 4 [ = 12]

SubParams = Reg to Reg (0), Const to Reg (1), Reg Memory to Reg (2), Memory to Reg (3)

Params = 2

Xors content of param 2 and 1 (1 XOR 2) and stores in 1

---

JMP/(JE or JZ)/(JNE or JNZ)/JGT/JLT/JGE/JLE

ID = 9

Size = 4 + 2 * 4 [ = 12]

SubParams [first 8 bit] = Plain (0), Jump if [R8 = ]Zero or equal (1), Jump if [R8 != ]not Zero or equal (2), Jump if R8 > 0 (3), Jump if R8 < 0 (4), Jump if R8 >= 8 (5), Jump if R8 <= 0 (6)

SubParams [second 8 bit] = To Const (3), To Reg (0), To Reg Mem (1)

Params = 1 64-bit integer [instruction index] or 1 32-bit registor

---

PUSH

ID = 10

Size = 4 + 4 [ = 8]

SubParams = Reg(0), Mem(2) (push PTR), Const(3)

Params = 1

Push item to stack also increments stack top pointer

---

POP

ID = 11 Size = 4 + 4 [ = 8] SubParams = Reg(0) Params = 1

Pop item to stack also increments stack top pointer

---

EXT

ID = 12

Size = 4

SubParams = Const (exit code)

Quit VM

---

SYSCALL

ID = 13

Size = 4

SubParams = NULL

---

PRINTREG

ID = 14

Size = 5

SubParams = NULL

Params = 1 (a registor)

NOTE: PRINTREG IS ONLY MEANT TO BE USED FOR DEBUGGING