Introduction:


Hello and welcome to my (Tyler Grusendorf) online x64 emulator written in TypeScript (JavaScript)! This emulator is still a work in progress so there might be a few bugs here and there.
Understanding computers and how they work is really a passion peice over hobby and if you really want to nerd out check out CPUville and Donn's Homemade computer! I've worked to sqush them all but, you know. Regardless there are currently Implemented Instructions.
As this is an emulator most Interrupts and Win APIs aren't implemented yet.

Take a look at the different sections for descriptions on each section in the emulator.
My biggest todos right now are making descriptions for each of the implemented instructions and to make up a tutorial to show how assembly works.
Lesson 01: Assembly Language... are you a masochist? lol

Limitations and Bugs:

Lets start off on the wrong foot! Bugs, Limitations & Problems!

Code View:

Registers:


A: General Purpose Register
B: General Purpose Register
C: General Purpose Register
D: General Purpose Register
SI: General Purpose Register
DI: General Purpose Register
R8: General Purpose Register
R9: General Purpose Register
R10: General Purpose Register
R11: General Purpose Register
R12: General Purpose Register
R13: General Purpose Register
R14: General Purpose Register
R15: General Purpose Register

BP: Stack Base Pointer. Stack pointer grows towards 0 from here. Should always use 32 bit reference EBP whan using.
SP: Stack Pointer. Should always use 32 bit reference ESP whan using.

; IP: Points to the next instruction to be executed. Shouldn't be changed manually in code! (ie don't use "mov EIP, 0x10") Use the flow control instructions. (like JMP mylabel)


All Registers can be accessed at different sizes:
For instance usinging the "A" register the full 32 bits would be accessed using EAX
AX is used for accessing the lower 16 bits
AL for the lower byte (8 bits)
And finally AH for acessing the higher 8 bits of the lower 16 bits
As an example if we have the following hex number in the D register: 0x12345678
EDX would return the whole number (0x12345678)
DX would return 0x5678
DH would return 0x56
DL would return 0x78


For the extended R registers you can access lower bits using the following:
R8 - The full 64-bit register.
R8D - D for Double Word (Lower 32-bits)
R8W - W for Word (Lower 16-bits)
R8B - B for byte (Lowest 8-bits)
Notice the only difference between the older registers and the newer R registers is there is no H option to get the lowest high byte (Like AH)


Segment registers DS, ES, FS, GS, SS are not used.

Flags

CF:Operation generated a carry or borrow
PF:Last byte has even number of 1's, else 0
AF:Denotes Binary Coded Decimal in-byte carry
ZF:Result was 0
SF:Most significant bit of result is 1
DF:Direction string instructions operate (increment or decrement)
OF:Overflow on signed operation
AC:Alignment check(486SX + only)
 
ID:Changeability denotes presence of CPUID instruction
 
These flags exist but aren't used for anything (and aren't shown):
TF:Trap flag(single step)
IF:Interrupt enable flag
NT:Nested task flag(286 + only), always 1 on 8086 and 186
RF:Resume flag(386 + only)
VM:Virtual 8086 mode flag(386 + only)
VIF:Virtual interrupt flag(Pentium +)
VIP:Virtual interrupt pending(Pentium +)

Memory View:

Output View:

Variables View:

Messages and Screenshots:

Operators:


+Adds two values
-Subtracts right from left
*Multiplies
/Divides (Integer Division)
MODRemainder of Integer Division
EQEquality chack
NENot Equal to
GTGreater than
LTLess than
GEGreater than or equal to
LELess than or equal to
ANDBitwise AND
ORBitwise OR
XORBitwise XOR
NOTBitwise NOT
SHLBitwise Shift bits left
SHRBitwise Shift bits right
LENGTH Gets the length (in bytes) of the defined variable.
Eg.
 .data
   msg db 'Hello $' ; 7 Letters long
 .code
   mov eax, LENGTH msg ; Puts 7 into EAX
[ and ]Used to get the contents at calcualted memory address of the operation within the parenthesis.

Keywords:


.CODETells the compiler the next section is code. REQUIRED
.DATATells the compiler the next section is data.
BYTETells the next instruction the value is byte sized.
WORDTells the next instruction the value is 2 bytes (Short).
DWORDTells the next instruction the value is 4 bytes (An Int).
DBUsed in .data to declare variable size of byte.
DWUsed in .data to declare variable size of word (Short). 2-bytes
DDUsed in .data to declare variable size of dword (Int). 4-bytes
DQUsed in .data to declare variable size of qword (long) (8 bytes).
DUP Used in .data to duplicate data during declaration.
What that means is lets say we have:
data db 0, 0, 0, 0
We can declare this using the dup command:
data db 4 DUP (0)
Which tells the compiler to put 0 valued byte into the data variable 4 times.
This is really useful when you have a large buffer for instance:
buffer db 80 DUP (0)
Will tell the compiler to fill the buffer variable with 80 bytes of zero.

Format:
<Variable Name> <Data Size (DB, DW, D, or DQ)> <Num of times to duplicate> DUP (<Value>)
<Value> can be any value that fits into the data size. As well at multipule values comma seperated:
data db 4 DUP (0, 1)
Is the same as:
data db 0, 1, 0, 1, 0, 1, 0, 1
ENDEnd program.
EXTRNPoints to an external function that should be included. See External Functions

Instructions:


Most instructions have two parameters (operands) Target and Source.
When an operation is performed the source and target are read and the operation does what it needs to before placing the result in the Target overwriting what was there. Source remains unchanged.
A good example would be this:
MOV ax, 4 ; Move 4 into ax
MOV bx, 3 ; Move 3 into bx
ADD ax, bx ; Read 3 from bx and read 4 from ax. Add the two numbers together and place in ax (result 7).
There are a few that just perform an operation using a single operand (Like INC that adds one to the Target) and a few that can use more than two operands (like ).
For operations Target Can be a Register or Memory Location. Source can be a Register, Memory Location, or Immidiate value (a number). Source and target cannot both be a memory location.
This list also includes instructions which are specifically not available to use here. Namely instructions that have been replaced in x64 or that involve privileged operations or threading.
I'm still working on adding documentation and examples to this section.
The following is a list of instructions that aren't implmeneted as of yet.
Sweet jesus that's a long list :-S

Implemented Interrupts:


0x05Print Screen
0x10Video InterruptsNone Implemented at the moment.
0x13 Disk Operations
(Not Implemented at the moment.)
Value of AH
0x0DISK - RESET DISK SYSTEM
0x1DISK - GET STATUS OF LAST OPERATION
0x2DISK - READ SECTOR(S) INTO MEMORY
0x3DISK - WRITE DISK SECTOR(S)
0x4DISK - VERIFY DISK SECTOR(S)
0x18DISKLESS BOOT HOOK - Called when a boot loader can't find the OS.
Terminates the running program.
0x21 DOS Software Interrupt 0x4C
Value of AH
0x0Program terminate.
0x1 Character input
Waits for a key to be pressed and then sets AL to the pressed key.
Echos the pressed key to the screen.
0x02Character output. Gets character from DL and writes to screen.
0x07 Direct console input without echo
Waits for a key to be pressed and then sets AL to the pressed key.
0x08 Console input without echo
Waits for a key to be pressed and then sets AL to the pressed key.
The key is also echoed to the screen.
0x09 Display string
Gets memory address from DX and reads a string from memory. The string must be terminated by a $ character.
Program terminate.

Implemented External APIS (Win API):


Handles System Calls from program.
64-Bit Calls to windows functions:
Microsoft x64 calling convention
Registers RCX, RDX, R8, R9 for the first four integer or pointer arguments (in that order)
Additional arguments are pushed onto the stack (right to left)
Return values placed in EAX
wikipedia stdcall
MessageBoxAint MessageBoxA(HWND hWnd, LPCSTR lpText, LPCSTR lpCaption, UINT uType);
ExitProcessvoid ExitProcess(); - Ends the program execution. Does not return.