twopassassembler

Two stage C assembler to the machine code.

twopassassembler

Two pass assembler:

This is free open source code.

It accepts an assembly language program as input and produces its machine language equivalent along with the information for the loader.
The assembling of source program to object code requires to accomplish following functions.

Opertion :

Simply convert the mnemonic opcodes to machine language equivalent.(e.g, LDA to 00)
Convert symbolic operands to their equivalent machine address (eg, LOOP to 2045) Allocate necessary memory. Convert data constants to internal machine equivalents. Write the object program and assembly listing.

Two pass assembler do these functions in two passes ,i.e., two times the input programs will be scanned/processed.

Pass 1 feeds into pass 2 :

PASS 1

After compiling the first program it generate the two files,symtab.txt and inter.txt * Assign addresses to all statements in the program. * Addresses of symbolic labels are stored. * Some assemble directives will be processed.

Input file :

Simple ARM assembly code where it add the numbers from 1 to 10.

COPY START 1000 MOV R0 0
MOV R1 10
ADD R0 R0 R1 SUBS R1 R1 1 BNE 1 B halt
$ END START

Example : C equivalent.

int total; int i;

total = 0;
for (i = 10; i > 0; i--) {
    total += i;
}

Output file generated:

inter.txt

1000 COPY START 1000 1000 MOV R0 0 1003 MOV R1 10 1006 ADD R0 R0 1009 R1 SUBS R1 100c R1 1 BNE 100f 1 B halt 1012 $ END START

symtab.txt

MOV 1000 ADD 1006 R1 1009 1 100f

PASS 2

* Translate opcode and symbolic operands.
* Generate data values defined by BYTE,WORD etc.
* Assemble directives will be processed.
* Write the object program and assembly listing.

Final instructions generated on this below file.

Output.txt

H^COPY^001000^12 T^001000^12^� E^001000

iqramali / twopassassembler

twopassassembler

twopassassembler