A simple bootstrap
-----2004.11.1 (C) Gr1x
To make a long story short, and enough material can be found about the PC's POST procedure, I'll just show my code and explain sth important steps, I think my source code is self-explaining enough 'cause it's short and easy to understand . I have tested it with a floppy disk, it's risky to test it with ur harddrive. If u did do it, I am not responsible for any damage u made : )
Environment :(Window Platform)
a.VMWare(Optional).If u don't want to reboot ur system many times, u should get this.
b: Nasm.(Essential). As u need it to compile ur code . u may use Ndisasm as well to disassemble the plain binary code compiled.
c:Visual C++ 6 or Visual Stdio .Net. As we have to write a EXE to write the bootstrap to floppy.
U may use WinHex to write bootstrap to floppy too instead of this writing a programme.
1>Write the bootstrap procedure
----------------------------bootstrap.asm-------------------------------------------------
;***************************************************
; bootstrap.asm: 2004-11-1 (C) Gr1x
; Email:gr1x@sina.com
;****************************************************
[ORG 0]
jmp 07C0h:start ; remember that BIOS loads this procedure in 0:7C00h, but don't count on registers like DS
;was initialized to 0. So we jump to it ourself.
msg db 'Hello Gr1x!',0x0
start:
; Update the segment registers
mov ax, cs
mov ds, ax
mov es, ax
mov si, msg ; Print msg
print:
lodsb ; loads charater at 0x7C0h:msg
mov ah, 0eh ;
int 10h
cmp al, 0 ;
jne print ;
jmp $
times 510-($-$$) db 0
dw 0000h ;or dw 0AA55h, u can write anything here , it seems that BIOS doesn't check this 2 bytes when
; it try to boot from a floppy disk
-----------------------------------------------------------------------------------------------------
OK , now compile it:
>nasm bootstrap.asm -o bootstrap.bin
2.Now , copy this bootstrap to floppy's boot sector. If u do it with WinHex , u can omit following.
I wrote a program which do this action.
------------------------------write_fd.cpp----------------------------------------------
//*********************************************
// BootStrap.cpp: 2004-11-1 (C) Gr1x
// Email:gr1x@sian.com
//***********************************************
#include <windows.h>
#include <winioctl.h>
#include <stdio.h>
#pragma comment(linker,"/subsystem:console" )
int main(int argc, char **argv)
{
HANDLE hDevice=NULL,hFile=NULL;
TCHAR szDevicename[64];
LPTSTR szBuff=NULL;
DISK_GEOMETRY Geometry;
BOOL bRet;
DWORD bytes,breadwrite,count;
if(argc!=2)
{
printf("Usage:%s filename\n",*argv);
exit(0);
}
__try
{
hFile=CreateFile(argv[1],GENERIC_READ,FILE_SHARE_READ,NULL,OPEN_EXISTING,0,NULL);
if (hDevice == INVALID_HANDLE_VALUE)
{
printf("Error in open file %s!\n",argv[1]);
__leave;
}
wsprintf(szDevicename,"\\\\.\\a:"); //change \\\\.\\a for \\\\.\\PHYSICALDRIVE0 if u wanna write harddisk.Risky!
hDevice = CreateFile( szDevicename,
GENERIC_READ|GENERIC_WRITE,
FILE_SHARE_READ|FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
0,
NULL
);
if (hDevice == INVALID_HANDLE_VALUE)
{
printf("Error in open floppy device!");
__leave;
}
DeviceIoControl(hDevice,FSCTL_LOCK_VOLUME, NULL,0,NULL,0,&count,NULL);
DeviceIoControl(hDevice,IOCTL_DISK_GET_DRIVE_GEOMETRY,NULL,0,&Geometry,sizeof(DISK_GEOMETRY),&count,NULL);
szBuff = (LPSTR)HeapAlloc(GetProcessHeap(),HEAP_ZERO_MEMORY,Geometry.BytesPerSector);
if ( szBuff == NULL)
{
printf("Error in HeapAlloc!");
__leave;
}
bytes = 512;
bRet = ReadFile(hFile, szBuff, bytes, &breadwrite, NULL);
if (bRet==FALSE || breadwrite<512)
{
printf("Error in read file!");
__leave;
}
printf("%d bytes read from %s\n",breadwrite,argv[1]);
bRet=WriteFile(hDevice,szBuff,bytes,&breadwrite,NULL);
if (bRet==FALSE || breadwrite<512)
{
printf("Error in write file to floppy!");
__leave;
}
if(!DeviceIoControl(hDevice,FSCTL_UNLOCK_VOLUME, NULL,0,NULL,0,&count,NULL))
printf("DeviceIoControl(hDevice,FSCTL_UNLOCK_VOLUME, NULL,0,NULL,0,&count,NULL) error!\n");
DeviceIoControl(hDevice,FSCTL_UNLOCK_VOLUME, NULL,0,NULL,0,&count,NULL);
printf("Write finished!\nBoot sector in HEX:\n");
for(int j=0,int i=0; i<512; i++)
{
unsigned char ch=(unsigned char) szBuff[i];
if (j==8) printf(" -");
if (j==16)
{
printf("\n");
j=0;
}
j++;
if (ch<0x10) printf(" %2x",ch);
else printf(" %2x",ch);
}
printf("\n");
}
__finally
{
if(szBuff!=NULL)
HeapFree(GetProcessHeap(),HEAP_NO_SERIALIZE,szBuff);
if(hDevice!=NULL)
CloseHandle(hDevice);
if(hFile!=NULL)
CloseHandle(hFile);
}
return 0;
}
--------------------------------------------------------------------------------------------
Don't ask me how to compile this cpp file!
3>Type following commad in CMD
>write_fd bootstrap.bin
4>OK, boot ur system with the floppy.God bless u!
