HACKER'S VIEW ....

Unknown

I started learning assembler a few months ago;

I have a lil' experience with TPascal an QB.

I have this problem for the ASSEMBLER MASTERS:

I wanted to write a code of mine directly into a

".com" file using the HaCkEr'S vIeW decode option.

As far I wrote jmps to do something it was good...

but I had an idea..

I wanted to write a name of a generic .txt file

directly into the memory( using stos ?), and then

i wanted to delete the file from the hard disk

calling back the name of the .txt file from memory

with some load instruction.

QUESTION IS:

HOW CAN I WRITE A STRING INTO MEMORY FROM AN

ALREADY COMPILED COM/EXE FILE?

Help Me please!!!

Unknown

Well, for COM files, to add code, the simplest way

to do it is to add a absolute JMP opcode at the beginning

(usually 256 bytes in) to the end of the code, execute

what you want to there, (i.e. load the string, delete, etc.)

execute the opcode that was replaced by inserting the

JMP instruction, and JMP back to the instruction right after

your original JMP.

For EXE files it's a bit more difficult. What kind of EXE?

MZ, PE, LE, NE?

Matthew Gross


URL:http://acheronx.resnet.tamu.edu

Unknown

Thanx for the help, but the matter was

How can I store a string directly into memory?

I mean I still don't know how to use

the STOSB etc. instructions.

Can you help me?

Unknown

: Thanx for the help, but the matter was

: How can I store a string directly into memory?

: I mean I still don't know how to use

: the STOSB etc. instructions.

: Can you help me?

Ok, assuming that you have the segment:offset address of the

string and the area that you want to write to:

Use MOV commands to transfer the address of the string's current

location in memory into DS:SI. Then, transfer the address of where

you want it to end up at in ES:DI.

MOV into CX the number of bytes (characters) in the string,

plus any terminating character, i.e. 0 or 24h at the end, etc.

Then:

REP MOVSB

Will do the actual moving of the procedure.

Post back if you have problems, or if you have to load the

string from a disk file to memory first, or you have problems

finding the address.

Matthew Gross

Acheron@Hotmail.com

http://acheronx.resnet.tamu.edu

Unknown

I got some concepts clearer now! Thanx!

What if I want to write a string into a

code? I mean..

Consider that I'm not creating an asm file

"ex novo" but I'm just hacking into a .com file

so that I'm NOT defining a string with the

common:

@String DB "this is a string",0

but I'm about to write directly into binary

using instructions like

MOV somewhere, "FirstCharOfString"

STORE somewhereElse,somewhere

and then

MOV somewhere ,"SecondCharOfString"

STORE somewhereElse + 1, somewhere

and so on...

This is my problem.

Help me, Master.

Unknown

A string in code just appears as:

This is my string0

where 0 is the null symbol. You just add the string

to the end of the code, and point the offset to the

first character. Make sure that your string is someplace

where it won't get executed, either, or it'll crash the

prog.

Matthew Gross


URL:http://acheronx.resnet.tamu.edu

Unknown

I DID IT THANX MAN!!!!!