As a practical exercise to do alongside Casey Muratori's series on performance programming, I developed a CPU simulator that supports a reduced instruction set. This simulator is capable of running a compiled executable or decompiling the executable back to x86 assembly. The goal I set for myself was to make it render something to a small framebuffer.
This simulator supports a reduced instruction x86 set. Here are the following instructions this simulator supports:
Arithmetic: mov, add, sub, cmp
Branching: jmp, jnz, je, jl, jle, jb, jbe, jp, jo, js, jge, jg, jae, ja, jnp, jno, jns, loop, loope, loopne, jcxz
You can mov to 16 bit registers (AX, BX, CX, DX) or use them as multiple 8 bit registers (AL, AH, BL, BH, etc.)
It supports moving to/from registers, memory, the accumulator, and segment registers.
Please see Testing/full_test_suite.asm for a full example of what this simulator and decompiler supports
Visualiser: The UI interprets memory location 0x00f0 onwards as a 64x64 framebuffer and will display on screen.
It will interpret every set of 3 bytes as RGB values.
This program currently runs exclusively as a UI. To run a program, you should compile your x86 assembly with nasm making
sure you've only used the reduced instruction set, and run the program in the simulator using this arg syntax:
8086_Simulator.exe program.asm
This simulator is tested using an .asm file which contains all supported instructions.
run_tests.bat compiles Testing/full_test_suite.asm using nasm, loads the binary into the simulator, and saves out the decompilation.
It then re-compiles this decompilation using nasm and then compares the original binary to the new binary created from the decompilation.
We know if this simulator's decompiler works well if the two compilations produce completely identical binary.