Synacor Challenge

Language used: Python.

Tasks

Virtual machine

In this challenge, your job is to use this architecture spec to create a virtual machine capable of running the included binary. Along the way, you will find codes; submit these to the challenge website to track your progress. Good luck!

Architecture

three storage regions
- memory with 15-bit address space storing 16-bit values
- eight registers
- an unbounded stack which holds individual 16-bit values
all numbers are unsigned integers 0..32767 (15-bit)
all math is modulo 32768; 32758 + 15 => 5

Binary format

each number is stored as a 16-bit little-endian pair (low byte, high byte)
numbers 0..32767 mean a literal value
numbers 32768..32775 instead mean registers 0..7
numbers 32776..65535 are invalid
programs are loaded into memory starting at address 0
address 0 is the first 16-bit value, address 1 is the second 16-bit value, etc

Execution

After an operation is executed, the next instruction to read is immediately after the last argument of the current operation. If a jump was performed, the next operation is instead the exact destination of the jump.
Encountering a register as an operation argument should be taken as reading from the register or setting into the register as appropriate.

Optcodes

Name	Code	Parameters	Notes
halt	0		stop execution and terminate the program
set	1	a b	set register `a` to the value of `b`
push	2	a	push `a` onto the stack
pop	3	a	remove the top element from the stack and write it into `a`; empty stack = error
eq	4	a b c	set `a` to 1 if `b` is equal to `c`; set it to 0 otherwise
gt	5	a b c	set `a` to 1 if `b` is greater than `c`; set it to 0 otherwise
jmp	6	a	jump to `a`
jt	7	a b	if `a` is nonzero, jump to `b`
jf	8	a b	if `a` is zero, jump to `b`
add	9	a b c	assign into `a` the sum of `b` and `c` (modulo 32768)
mult	10	a b c	store into `a` the product of `b` and `c` (modulo 32768)
mod	11	a b c	store into `a` the remainder of `b` divided by `c`
and	12	a b c	stores into `a` the bitwise and of `b` and `c`
or	13	a b c	stores into `a` the bitwise or of `b` and `c`
not	14	a b	stores 15-bit bitwise inverse of `b` in `a`
rmem	15	a b	read memory at address `b` and write it to `a`
wmem	16	a b	write the value from `b` into memory at address `a`
call	17	a	write the address of the next instruction to the stack and jump to `a`
ret	18		remove the top element from the stack and jump to it; empty stack = halt
out	19	a	write the character represented by ascii code `a` to the terminal
in	20	a	read a character from the terminal and write its ascii code to `a`; it can be assumed that once input starts, it will continue until a newline is encountered; this means that you can safely read whole lines from the keyboard and trust that they will be fully read
noop	21		no operation

Running

Run Virtual Machine by command:

python main.py

Parameters

-l: load dump file (excepte file name after -l option)
-d: display debug information during running program

Example:

python main.py -l save.dump -d

Decompiling

Run decompile script. The script requires dump file to operate on.

python decompile.py -l save.dump

Other puzzles notes

After running the virtual machine, we can play in the text advature hidden in the given program. In the game we can find another puzzles:

dplocki/synacor-challenge