assembler

C++ program that converts SUBLEQ Assembly text file to an object file format.

It's part of a series of programs we're making:

1. Kernel
2. Compiler
3. Assembler
4. Linker
5. Simulator
6. Hardware

Summary

To build it, simply run make.

Usage:

subleq-asm <assembly_file> <object_file>

SUBLEQ Assembly

This is a special kind of Assembly language; it has only one instruction, called SUBLEQ.

The SUBLEQ Instruction

It has the following format:

SUBLEQ A B C

Here's what it does, in a kind of pseudo-code:

SUBLEQ(address A, address B, address C)
{
    VALUE(B) = (VALUE(B) - VALUE(A))

    if (VALUE(B) <= 0)
        goto C
    else
        GOTO NEXT_INSTRUCTION
}

All three operands (A, B and C) are memory addresses. VALUE(A) means the value on memory address A.

The File format

The whole file has the following format:

// Comments to end-of-line

.export
    // Exported symbols

.data
    // Specify data on memory

.text
    // Instructions
  label:
    // Mode instructions

Now, some rules for the .text part:

• Instructions come on the format SUBLEQ A B C
• A, B and C can be numbers (memory addresses starting from zero) or labels for things on the .data part

.data
    numberTwo: 2
	numberMinusThree: -3
	minusOne: -1

.text
    SUBLEQ 3 2 1
    // Which is the same as
	SUBLEQ minusOne numberMinusThree numberTwo

• You can suppress SUBLEQ, merely writing A B C

// Same as above example
.text
    3 2 1
	minusOne numberMinusThree numberTwo

• If you don't specify C it is assumed to be the next instruction's address.

.text
    // So this means it will always go to the
	// next instruction
    3 2

• Finally, if you don't provide B we assume it's the same as A.

.text
    // So this...
	3
	// ...actually means this...
    3 3
    // Which also has the next address implied

Summary

So, in the end, these are all valid statements:

.text
  label:
    INSTRUCTION A B C
	            A B C
				A B
				A

Example

The following is an example of a SUBLEQ Assembly file:

.export
    label
.data
    A 5
    B 123
.text
  label:
    A B label
    A 0xFF C

For more, check out our assembly-examples repository.

Object Code

This program translates a well-formed source in previous Assembly language to an object code.

It is a binary file with the following format:

What                      Raw size
---------------------------------------------
Count of exported symbols    (uint32_t)
All exported symbols:
    Symbol name              (null-ended char[])
	Symbol address           (uint32_t)

Count of pending references  (uint32_t)
All pending references:
    Symbol name              (null-ended char[])
	Number of references to  (uint32_t)
    this symbol
	All references:
	    Reference            (uint32_t)
Number of relative addresses (uint32_t)
All relative addresses:
    Address                  (uint32_t)
Assembled code size          (uint32_t)
Assembled code:
    s