carlosrafaelgn/asm86

A JavaScript assembly x86 compiler + emulator for educational purposes

asm86's Issues

Menus not closing, and windows not moveable

http://carlosrafaelgn.com.br/asm86/

Menus (eg: language) do not close when I click somewhere else, and when I try to move windows (eg: Console) it just selects everything.

support for equates?

Nice work. Does it support equates?

example:

SOME_CONSTANT equ 0x3

imul flags on particular case of 2 x maxint

Looks to me like imul is not setting flags properly on this particular case! Thanks, Erik

mov eax, 0x2
mov ebx, 0x7FFFFFFF
mov edx, 0xDEADBEAF  
imul ebx                                        ; <----- after this CF & OF should be set/true/1 but they are cleared

mov eax, 0x4
mov ebx, 0x7FFFFFFF
mov edx, 0xDEADBEAF
imul ebx                                        ; CF & OF properly set to true/1

mov eax, 0xFFFFFFFF
mov ebx, 0xFFFFFFFF
mov edx, 0xDEADBEAF
imul ebx                                       ; CF & OF properly set to false/0


mov ebx, 0xDEADBEAF
ret

how it work?

for the assembly x86 emulator, how it work? can you share the tutorial etc. Why it differ with NASM assembly code?

SAR bug

Hi,
here's the issue.

"Using the SAR instruction to perform a division operation does not produce the same result as the IDIV instruction. The quotient from the IDIV instruction is rounded toward zero, whereas the “quotient” of the SAR instruction is rounded toward negative infinity. This difference is apparent only for negative numbers. For example, when the IDIV instruction is used to divide -9 by 4, the result is -2 with a remainder of -1. If the SAR instruction is used to shift -9 right by two bits, the result is -3 and the “remainder” is +3; however, the SAR instruction stores only the most significant bit of the remainder (in the CF flag)."
[https://software.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf]

When I run this code
mov al, -9
sar al, 2
the result stored in al is 0x3D but it should be 0xFD(-3)
Tested on my local machine.

Feature request: Accept different hex notation

This works:

0x34

however several documents also show:

34h

Would be great if we can get this to read either. Thank you.

Question on syntax

The below snippet is from the book "Practical Reverse Engineering"

mov   dword ptr [eax], 1
mov   ecx, [eax]
mov   [eax], ebx
mov   [esi+0x34], eax
mov   eax, [esi+0x34]
mov   edx, [ecx+eax]

This fails to step through with:

Invalid writing address: 0x00000000

Is there a specific syntax I need to use? Thank you.

ADD assumes 32-bit register size when setting flags

e.g.:

mov al,255
add al,1

CF will not be set, when it should be. The code assumes that the register (AL) is 32-bit and checks flags accordingly.

Can you add an English UI?

Thank you in advance.

About neg

I compile and run this asm on my linux:

mov al, -128
neg al

Overflow flag will be 1 after neg al
But in this emulator, overflow flag is 0 after neg al
Is this a bug? I'm not very familiar with asm.

Thanks!

print value of variable at console

can you help me, how to print value of variable at console after summation of the variables value?

example:
MOV AL, NUM1 ; NUM1=15d
ADD AL, NUM2 ; NUM2=34d
ADD AL, NUM3 ; NUM3=56d

how i can print the total value in console? I'm very stuck even I refer the load example. Thank you!