peter-feeney / vm

Simple virtual machine written in C that emulates a MIPS-like assembly language.

VM

What

Simple virtual machine written in C that emulates a MIPS-like assembly language on a fictional CPU.

Why

I created this primarily as a way to have fun with C, and to reacquaint myself with some assembly and elementary systems programming concepts. This repository is a space where I can mess around with things in C that interest me if I want to do so.

There were various points during the making of this project where I had to choose between writing maintainable code or using some cool feature of C. I chose the latter option every time. So if you're a potential employer and you're reading this then I want you to know that I would never create monstrosities like the macros in eval.c on the job.

How

The VM takes in instructions encoded in binary and spits out the output of those instructions.

Supported instructions include:

• PSH [arg1]: Push argument onto stack.
• ADD [reg_number] [arg1] [arg2]: Store arg1 + arg2 in Reg[reg_number]
• POP: Pop argument from stack.
• SET [reg_number] [arg1]: Set reg_number to value arg1.
• DIV [reg_number] [arg1] [arg2]: Store arg1 / arg2 in Reg[reg_number]
• MUL [reg_number] [arg1] [arg2]: Store arg1 * arg2 in Reg[reg_number]
• SUB [reg_number] [arg1] [arg2]: Store arg1 - arg2 in Reg[reg_number]
• GLD [reg_number]: Load value from reg_number to the stack.
• GPT [reg_number]: Push top of stack onto Reg[reg_number]
• AND [reg_number] [arg1] [arg2]: Store arg1 & arg2 in Reg[reg_number]
• MOD [reg_number] [arg1] [arg2]: Store arg1 % arg2 in Reg[reg_number]
• OR [reg_number] [arg1] [arg2]: Store arg1 | arg2 in Reg[reg_number]
• NOT [reg_number] [arg1]: Store ~arg1 in Reg[reg_number]
• XOR [reg_number] [arg1] [arg2]: Store arg1 ^ arg2 in Reg[reg_number]
• BEQ [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 == arg2
• BNE [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 != arg2
• BLT [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 < arg2
• BGT [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 > arg2
• BEQZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 == 0
• BGE [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 >= arg2
• BLE [arg1] [arg2] [arg3]: Branch to location specified by arg3 if arg1 <= arg2
• BLTZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 < 0
• BGEZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 >= 0
• BNEZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 != 0
• BLEZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 <= 0
• BGTZ [arg1] [arg2]: Branch to location specified by arg2 if arg1 > 0
• JMP [arg1]: Go to location specified by arg1.
• SYSCALL [arg1]: Scan in number into Reg[arg1] if Reg[SYSTEM] == 1, otherwise print out whatever is in Reg[arg1]
• HLT: Stop program from running. (Needed at the end of any input)

When you start the program it'll ask you for the name of a file. Enter in the name of a properly encoded text file -- it must be in binary for now, but I'll work on adding in support for string input later on.

What makes a properly encoded text file? Read the source code of IO.c and do a little bit of reverse engineering and you'll be able to figure it out. Again, this project is exploratory in nature and practical usage wasn't really a prime consideration here.

Feel free to send all questions, comments, suggestions for improvement, hate mail, love letters, job offers (!), etc. to [email protected].