Thread: EXEcutable file

Can i?
Can i edit a exe file via a code writeen in c?
I just explore the file by :

Code:

#include<stdio.h>
#include<stdlib.h>

struct EXE{
		char id[2];
		unsigned last;
		unsigned pages;
		unsigned reloc_items;
		unsigned headersize;
		unsigned minpara;
		unsigned maxpara;
		unsigned ss;
		unsigned sp;
		unsigned chksum;
		unsigned ip;
		unsigned cs;
		unsigned first_reloc;
		unsigned ovr;
		};

void main(int argc,char *argv[])
	{
	FILE *fp;
	struct EXE exe;
	if((fp=fopen(argv[1],"rb"))==NULL)
		{
		puts("\n\nUsage: EXE exe_file_name\n");
		exit(-1);
		}
	printf("abhinay shinde\n\n");
	printf("Dept. of computer Science maharashtra.\n\n");
	fread(&exe,sizeof(exe),1,fp);
	printf("Id (usually MZ)........................%c%c\n",exe.id[0],exe.id[1]);
	printf("Total bytes on the last sector.........%05u  %04x\n",exe.last,exe.last);
	printf("Total sectors..........................%05u  %04x\n",exe.pages,exe.pages);
	printf("No of reloc table items................%05u\n",exe.reloc_items);
	printf("Header size in paras...................%05u\n",exe.headersize);
	printf("Min paras required.....................%05u\n",exe.minpara);
	printf("Max paras required.....................%05u\n",exe.maxpara);
	printf("SS.....................................%05u  %04x\n",exe.ss,exe.ss);
	printf("SP.....................................%05u  %04x\n",exe.sp,exe.sp);
	printf("CheckSum...............................%05u\n",exe.chksum);
	printf("IP.....................................%05u  %04x\n",exe.ip,exe.ip);
	printf("CS.....................................%05u  %04x\n",exe.cs,exe.cs);
	printf("Offset of the last reloc item..........%05u\n",exe.first_reloc);
	printf("Overlay No.............................%d\n",exe.ovr);
	}

now i want to edit it .
is it possible?

[code][/code]tagged by Salem

u can modify a exe file but u need to know assembly

i can use a dissembler to do it

this is a code in asm that adds 2 number

Code:

mov al 5h
mov dl 5h

add al dl

if i dump the exe file and veiw the content that does the same thing above this is what i c .If i need to change 5h which is 5 in decimal to say 10 then this is what i will do .I will open the exe or com file with a dissembler and modify the al 5h to

Code:

al ah             ;in decimal that is 10 it

mosrt of the things are quite fimilair like SS means Segment stack, EC means extra segment u need to know assembly before attempting to write a dissembler ...
Thats basically it ....