LEGv8-Disassembler

A disassembler for LEGv8 machine code as required by Computer Science 321 @ Iowa State University, Fall 2021.

Supported Instructions

The supported instructions are the following:

• ADD
• ADDI
• AND
• ANDI
• B
• B.cond (This is a CB assemblyInstruction in which the Rt field is not a register, but a code that indicates the condition extension)
  • 0: EQ
  • 1: NE
  • 2: HS
  • 3: LO
  • 4: MI
  • 5: PL
  • 6: VS
  • 7: VC
  • 8: HI
  • 9: LS
  • a: GE
  • b: LT
  • c: GT
  • d: LE
• BL
• BR (Rn field has the branch target)
• CBNZ
• CBZ
• EOR
• EORI
• LDUR
• LSL (shamt field encodes the shift amount, while Rm is unused)
• LSR (shamt field encodes the shift amount, while Rm is unused)
• ORR
• ORRI
• STUR
• SUB
• SUBI
• SUBIS
• SUBS
• MUL

Apart from these instructions, there are four additional instructions that serve the purposes of debugging with the LEGv8 emulator provided in the course.

The following explanations are a snippet from the project requirements by Dr. Jeremy Sheaffer.

• PRNT: This is an added assemblyInstruction (part of our emulator, but not part of LEG or ARM) that prints a register name and > its contents in hex and decimal. This is an R assemblyInstruction. The opcode is 11111111101. The register is given in the Rd > field.
• PRNL: This is an added assemblyInstruction that prints a blank line. This is an R assemblyInstruction. The opcode is 11111111100.
• DUMP: This is an added assemblyInstruction that displays the contents of all registers and memory, as well as the disassembled > program. This is an R assemblyInstruction. The opcode is 11111111110.
• HALT: This is an added assemblyInstruction that triggers a DUMP and terminates the emulator. This is an R assemblyInstruction. The > opcode is 11111111111

Build

javac Main.java

Run

java Main $1

...where $1 refers to the file location of the machine code to parse.

Example

java Main machine_code

Disclaimer

The above code was authored by yjohnson-dev (henceforth "I") for the purposes of a grade in Computer Science 321: "Computer Architecture" by Dr. Jeremy Sheaffer. It is provided for the explicit purpose of showcasing work. Usage of this code for any reason, especially that of a grade in the selfsame course, is discouraged. I am in no way liable nor accountable for any cases of plagiarism or dishonesty concerning academics. This code comes with no warranties nor guarantees.