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----------------------------------------------
//*********************************************
// write_fd.cpp: 2004-11-1 (C) Gr1x
// Email:gr1x@sian.com
//***********************************************
#include <windows.h>
#include <winioctl.h>
#include <stdio.h>
#pragma comment(linker,"/subsystem:console" )
void Banner()
{
printf("---------------------------------------------/n");
printf(" write_fd:write a file to floppy in raw mode/n");
printf(" author:gr1x email:gr1x@sian.com/n");
printf(" usage:write_fd filename/n");
printf("---------------------------------------------/n);
}
int main(int argc,char **argv)
{
HANDLE hDevice=NULL,hFile=NULL;
TCHAR szDevicename[64];
LPTSTR szBuff=NULL;
DISK_GEOMETRY Geometry;
BOOL bRet;
DWORD bytes,bread,count;
Banner();
if(argc!=2)
{
printf("Usage:%s filename/n",*argv);
exit(0);
}
__try
{
hFile=CreateFile(argv[1],GENERIC_READ,FILE_SHARE_READ,NULL,OPEN_EXISTING,NULL);
if (hDevice == INVALID_HANDLE_VALUE)
{
printf("Error in open file %s!/n",argv[1]);
__leave;
}
wsprintf(szDevicename,"////.//a:");
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,&count,NULL); DeviceIoControl(hDevice,IOCTL_DISK_GET_DRIVE_GEOMETRY,&Geometry,sizeof(DISK_GEOMETRY),NULL); szBuff = (LPSTR)HeapAlloc(GetProcessHeap(),HEAP_ZERO_MEMORY,Geometry.BytesPerSector*2); if ( szBuff == NULL) { printf("Error in HeapAlloc!"); __leave; } bytes = 512*2; bRet = ReadFile(hFile,szBuff,bytes,&bread,NULL); if (bRet==FALSE || bread<512) { printf("Error in read file!"); __leave; } printf("%d bytes read from %s/n",argv[1]); bRet=WriteFile(hDevice,NULL); if (bRet==FALSE || bread<512) { printf("Error in write file to floppy!"); __leave; } if(!DeviceIoControl(hDevice,FSCTL_UNLOCK_VOLUME,NULL)) printf("DeviceIoControl(hDevice,NULL) error!/n"); DeviceIoControl(hDevice,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.bin4>OK,boot ur system with the floppy.God bless u!
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