Recent Posts

21

Other Discussion / Re: Looking for .COM program sources in NASM Assembly

« Last post by Frank Kotler on September 05, 2022, 02:38:16 PM »

Hi Paolo,

Welcome to the forum.

Have you looked in Example Code? It is not well indexed, but there should be at least some DOS .com code there.

I'll try to get back to you with more tips.

To others... Paolo Amoroso was sent here from clax86.

Best,
Frank

22

Programming with NASM / Re: Optimizing NASM Assembler codes in Windows x86

« Last post by Frank Kotler on September 05, 2022, 02:18:58 PM »

Thank you, Fred!

I hadn't decoded decoded his shellcode, but would have before I ran it.
He's gone in just a second.

Best,
Frank

23

Other Discussion / Looking for .COM program sources in NASM Assembly

« Last post by amoroso on September 05, 2022, 01:22:56 PM »

I'm looking for source code of MS-DOS .COM programs in real-mode 8086 Assembly written in NASM syntax. Any repositories or recommendations?

I'm learning Assembly programming under MS-DOS (and MikeOS) and cross-developing on Linux with NASM. To avoid the complexity of x86 segmentation, for the time being I prefer to focus on single-segment programs, as I plan to write small programs anyway. So I'd like to study examples of how such systems organize and reference data and code. I searched a bit but found remarkably little .COM code.

24

Programming with NASM / Re: Optimizing NASM Assembler codes in Windows x86

« Last post by fredericopissarra on September 05, 2022, 01:02:42 PM »

Very funny how you tried to inffect somebody computers with Trojan:Script/Wacatac.Html...

To the moderator I recommend deleting this and ban the user.

PS: Decode (do not run!) the byte stream and let the antivirus do its trick...

25

Programming with NASM / Re: Optimizing NASM Assembler codes in Windows x86

« Last post by Frank Kotler on September 05, 2022, 10:11:37 AM »

Shellcode has rather a bad reputation. Why are you using it?

Best,
Frank

26

Programming with NASM / Optimizing NASM Assembler codes in Windows x86

« Last post by SHITTY23 on September 04, 2022, 09:21:34 PM »

I am a novice in assembler programing, I will will appreciate if someone could review these NASM assembler code for me. Is about encoder decoder.
The encoder performs the following:

• pads the shellcode with NOP opcodes so it is 4 bytes aligned
• a random byte is generated for each 4 bytes of the shellcode
• the 4 bytes are put in the reverse order and XORed with the XOR byte
• process is repeated until the 0x9090aaaa marker is reached

For those good at NASM assembler for Microsoft Windows, please could you optimize this code? the Code is working but takes lot of time. The shellcode is a windows/meterpreter/reverse_tcp   x86 from msfvenom.

Code: [Select]

global main

; gone
; Frank



27

Programming with NASM / Re: How to modify value of symbol?

« Last post by Frank Kotler on September 02, 2022, 03:07:22 AM »

Is this any help?

https://forum.nasm.us/index.php?topic=1769.

Best,
Frank

28

Programming with NASM / Re: How to modify value of symbol?

« Last post by debs3759 on September 02, 2022, 12:35:33 AM »

If you use %define instead of %assign, it assembles. Reading the manual, I believe it acts the same, but accepts memory addresses as part of the macro.

29

Programming with NASM / How to modify value of symbol?

« Last post by radlyeel on September 01, 2022, 09:14:47 PM »

Does NASM have something like as's .SET, which changes the value of a symbol?  I *thought* %assign would be my friend, but alas, I was wrong yet again  It would be useful to build a linked list, like this:

Code: [Select]

default rel   
%assign lnk 0
%macro node 3 ; usage: node "name". 4, 7
    db %2     ; insert name length
    db %1     ; insert name
    align 8, db 0 ; pad 0s to 8-byte boundary
    dq %3     ; store value
    dq lnk        ; store link to preceding node
    %assign lnk $-16 ; set new value of link for next node
%endmacro

; satisfy NASM, ld, an lldb for examining results
global _main
_main: jmp $
node "OUN",2, 1
node "TROIS",5,3
With that, I get this:

Code: [Select]

$ nasm -g -f macho64 -o demo.o demo.s
demo.s:15: error: non-constant value given to `%assign'
demo.s:9: ... from macro `node' defined here
demo.s:16: error: non-constant value given to `%assign'
demo.s:9: ... from macro `node' defined here


30

Other Discussion / Re: introduction

« Last post by debs3759 on August 30, 2022, 10:05:00 PM »

Welcome to the forums. What OS do you write code for? We don't have a lot of active members, but among us we cover most common OS.