I wonder what's the best way to determine where the MZ part of an EXE file ends, and the attached extended executable starts (can be PE/LE/LX/NE/COFF etc ...).
I found this website: http://www.delorie.com/djgpp/doc/exe/ which tries to explain it, but I never get the expected result. I always end up with an offset way beyond the actual PE or LX start offset.
// LXInfo.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
struct EXE {
unsigned short signature; /* == 0x5a4D */
unsigned short bytes_in_last_block;
unsigned short blocks_in_file;
unsigned short num_relocs;
unsigned short header_paragraphs;
unsigned short min_extra_paragraphs;
unsigned short max_extra_paragraphs;
unsigned short ss;
unsigned short sp;
unsigned short checksum;
unsigned short ip;
unsigned short cs;
unsigned short reloc_table_offset;
unsigned short overlay_number;
};
struct EXE_RELOC {
unsigned short offset;
unsigned short segment;
};
int _tmain(int argc, _TCHAR* argv[])
{
struct EXE header1;
char sFile[]="c:\\register.dll";
unsigned int extra_data_start;
char test;
FILE *fp;
fp = fopen(sFile, "rb");
fread(&header1,sizeof(struct EXE),1,fp);
//read the header
printf("EXE Signature: %x \n", header1.signature);
printf("Bytes in last block: %08x \n", header1.bytes_in_last_block);
printf("Blocks in file: %08x \n", header1.blocks_in_file);
printf("Number of relocations: %08x \n", header1.num_relocs);
printf("Header paragraphs: %08x \n", header1.header_paragraphs);
printf("Min. extra paragraphs: %08x \n", header1.min_extra_paragraphs);
printf("Max. extra paragraphs: %08x \n", header1.max_extra_paragraphs);
printf("Initial SS value: %08x \n", header1.ss);
printf("Initial SP value: %08x \n", header1.sp);
printf("Checksum value: %08x \n", header1.checksum);
printf("Initial CS value: %08x \n", header1.cs);
printf("Initial IP value: %08x \n", header1.ip);
printf("Relocation table offset: %08x \n", header1.reloc_table_offset);
printf("Overlay number: %x \n", header1.overlay_number);
printf("\n");
printf("Start of EXE data: %08x \n", header1.header_paragraphs * 16L);
//calculate end of MZ EXE, according to Delorie
extra_data_start = header1.blocks_in_file * 512L;
if (header1.bytes_in_last_block)
extra_data_start -= (512 - header1.bytes_in_last_block);
printf("End of EXE data: %08x \n", extra_data_start);
// let's read the first two bytes after the MZ EXE data. This should give us a P and E on windows, or L and X on OS/2...
fseek(fp,extra_data_start,SEEK_SET);
fread(&test,1,1,fp);
printf("test char: %c \n", test);
fread(&test,1,1,fp);
printf("test char: %c \n", test);
fclose(fp);
getch();
return 0;
}
Read the following article: An In-Depth Look into the Win32 Portable Executable File Format.
You should also read up on the The Portable Executable File Format
For example, to get the offset of the IMAGE_NT_HEADERS
you would do like this:
IMAGE_DOS_HEADER* pdos = (IMAGE_DOS_HEADER*)peBuffer;
IMAGE_NT_HEADERS* pnt = (IMAGE_NT_HEADERS*)((DWORD)pdos + pdos->e_lfanew);