my-little-asm

mla is my custom Assembly-like language, implemented from scratch in C++. It has an assembler (to create machine code), simulator (to execute/test it) and translator (to convert to x86/IA-32 assembly).

This is an example on how Assembly languages work - a set of human-readable instructions that are translated into machine code. Normally the language would be designed for some hardware to execute, but in our case we simulate it step by step.

With our basic instruction set we can potentially write any existing program out there - also called Turing-completeness.

We have a parser that reads each instruction on the text file and converts them into integers - indexing all 14 possible instructions.

The output file is then fed into the simulator, that actually implements those instructions.

Finally, you can convert the resulting machine code into actual x86/IA-32 code. Then, use nasm and ld to create a standalone executable!

Usage

First, make sure to compile everything by doing:

$ make

Then, write any program according to the language definition below - saving with the .asm extension. See sample programs under the examples/ folder.

Then:

$ ./assembler file.asm file.o     # assemble file.asm to file.o
$ ./simulator file.o              # execute file.o
$ ./translator file.o             # converts file.o to file.s

file.s is a working x86 Assembly code file. You can create a standalone executable of it with nasm and ld:

$ nasm file.s -o file.obj -f elf -F stabs
$ ld file.obj -o file
$ ./file

Sample code

SECTION TEXT
LABEL:   INPUT  N1
         COPY   N1,    N2     ; comment
		 COPY   N2,    N3[0]  ; wow, array support!
		 COPY   N3[0], N3[1]
		 OUTPUT N3[1]
		 STOP

SECTION DATA
N1: SPACE
N3: SPACE  4        ; Array of size 4
N2: CONST  -0x10    ; Look ma, hex constant!

Language definition

mla follows a MIPS Assembly-like syntax.

Highlights:

• 14 instructions.
• ; starts comment until the end of line.
• Labels references memory addresses.
• Accumulator register (ACC) implied on arithmetic instructions.
• Files with .asm extension.

Code is divided in two sections:

• Data section (for variables and constants)
• Text section (for actual code)

Instructions

Name	Instruction	Description
Add	ADD	ACC <- ACC + MEM[OP]
Subtract	SUB	ACC <- ACC - MEM[OP]
Multiply	MULT	ACC <- ACC * MEM[OP]
Divide	DIV	ACC <- ACC / MEM[OP]
Jump Unconditional	JMP	PC <- OP
Jump if Negative	JMPN	If ACC < 0 then PC <- OP
Jump if Positive	JMPP	If ACC > 0 then PC <- OP
Jump if Zero	JMPZ	If ACC = 0 then PC <- OP
Copy	COPY	MEM[OP2] <- MEM[OP1]
Load from Memory	LOAD	ACC <- MEM[OP]
Store into Memory	STORE	MEM[OP] <- ACC
Store Input	INPUT	MEM[OP] <- STDIN
Output Memory	OUTPUT	STDOUT <- MEM[OP]
Stop Execution	STOP	stops program

Note:

• MEM[OP] means memory address specified by operand and PC is the program counter (current instruction address).

Directives

Name	Effect
SECTION TEXT	Signals begin of instructions.
SECTION DATA	Start of data definitions.
SPACE	Saves an empty space on memory for data storage.
SPACE N	Saves an empty array in memory of size N.
CONST X	Saves a constant of value X in memory.

Contact

Hello, there! I'm Alexandre Dantas and I programmed this lovely thing over two weeks. Don't take this project too seriously, mla was made as an assignment for a System Software class on my Computer Science .

• Website: http://alexdantas.net/
• Email: eu@alexdantas.net