Re: Windows,grub and grub2

[Viswesh S]

Hi,



----- Original Message ----
> From: Viswesh S <address@hidden>
> To: The development of GRUB 2 <address@hidden>
> Sent: Tuesday, 14 October, 2008 5:04:53 PM
> Subject: Re: Windows,grub and grub2
> 
> Hi,
> 
> 
> 
> ----- Original Message ----
> > From: Bean 
> > To: The development of GRUB 2 
> > Sent: Monday, 29 September, 2008 4:20:57 PM
> > Subject: Re: Windows,grub and grub2
> > 
> > On Mon, Sep 29, 2008 at 1:18 PM, Viswesh S wrote:
> > > Hi,
> > >
> > >
> > >
> > > ----- Original Message ----
> > >> From: Bean 
> > >> To: The development of GRUB 2 
> > >> Sent: Tuesday, 23 September, 2008 7:20:49 PM
> > >> Subject: Re: Windows,grub and grub2
> > >>
> > >> On Tue, Sep 23, 2008 at 4:23 PM, Viswesh S wrote:
> > >> >
> > >> >
> > >> >
> > >> >
> > >> > ----- Original Message ----
> > >> >> From: Bean
> > >> >> To: The development of GRUB 2
> > >> >> Sent: Monday, 22 September, 2008 9:10:26 AM
> > >> >> Subject: Re: Windows,grub and grub2
> > >> >>
> > >> >> On Tue, Sep 9, 2008 at 2:00 PM, Viswesh S wrote:
> > >> >> > Below is the dump of screen output while chainloading the ntfsnew 
> file.
> > >> >> > ***************************************
> > >> >> > DI=CFF0 SI=07EE BP=1FF0 SP=1FE8 BX=0000 DX=0000 CX=0000 AX=0000
> > >> >> > CS=0000 SS=0000 DS=0000 ES=0000 FG=0246 IP=7C57
> > >> >> >
> > >> >> > DI=7FF0 SI=07EE BP=1FF0 SP=7BF4 BX=55AA DX=0000 CX=0000 AX=0100 
> CX=07C0
> > >> >> > DS=07C0 ES=0000 FG=0007 IP=0082
> > >> >> > ******************************************
> > >> >> > Could you please let me know the way to disassemble the binary file 
> > without
> > >> >> > any header.The way in which you decoded the boot record.
> > >> >> >
> > >> >> > Also one more thing to let you know is that,
> > >> >> >
> > >> >> > with the grub-1.96 ( without the chainloader patch of 
> disk->dev->read() 
> > ) ,
> > >> >> > with windows2003 in partition 1 and linux in partition 3, when we
> > >> chainload,
> > >> >> > if we look at the partition table passed to another bootloader ie 
> > location
> > >> >> > 0x7be - we can see that it is junk, but the surprising point is 
> > >> >> > that, 
> in
> > >> >> > this case as I have mentioned in my first mail, windows boots up 
> > >> >> > from
> > >> >> > grub2.So it is that the partition table is not required for the 
> > chainloader
> > >> >> > thing and just the boot record is sufficient
> > >> >>
> > >> >> Hi,
> > >> >>
> > >> >> Oh, sorry for another long delay. I disassemble the file with ida,
> > >> >> which is an amazing tool. I don't know if there is open source
> > >> >> alternative, please let me know if you find one.
> > >> >>
> > >> >> The output from ida is in masm format, I modify it a bit so that it
> > >> >> can be compiled using nasm. Please note that nasm doesn't generate the
> > >> >> same binary file as original one, but you can get an idea what it
> > >> >> does.
> > >> >>
> > >> >> From the output, the program fails at the second int 13 call, int
> > >> >> 13/ah = 48h. Although I notice that DL=0, which is not supposed to
> > >> >> happen. Perhaps you can add a grub_printf in grub_chainloader_boot to
> > >> >> show the value of boot drive:
> > >> >>
> > >> >> static grub_err_t
> > >> >> grub_chainloader_boot (void)
> > >> >> {
> > >> >>  grub_printf ("boot_drive=%d\n", boot_drive);
> > >> >>  grub_chainloader_real_boot (boot_drive, boot_part_addr);
> > >> >>
> > >> >>  /* Never reach here.  */
> > >> >>  return GRUB_ERR_NONE;
> > >> >> }
> > >> >>
> > >> >> --
> > >> >> Bean
> > >> >>
> > >> >>
> > >> >
> > >> > Hi,
> > >> >
> > >> > The value of boot drive is 0x80.
> > >> >
> > >> > This was the same value in disk->drive also.
> > >>
> > >> Hi,
> > >>
> > >> Interesting, perhaps %dx is changed somewhere. Please try the
> > >> following patch, it dumps the value of %dx just before jumping to the
> > >> boot sector.
> > >>
> > >> --
> > >> Bean
> > >
> > > The patch works and now Windows is booting perfectly fine from Grub2.
> > >
> > > I will go through the assembly and try to understand what modifications 
> > > you 
> > have done.So there is a problem in Grub2 code, which needs to be fixed ?
> > >
> > > Till this point, I was chainloading grub from Grub2 and then chainloading 
> > Windows2008 from it.
> > >
> > > Thanks for the consistent help till this point and for the future also.
> > 
> > Hi,
> > 
> > That's strange, the patch doesn't do anything except output the value of dx:
> > 
> >    /* set up to pass boot drive */
> >    popl    %edx
> > +    movl    %edx, %edi
> > 
> >    /* ESI must point to a partition table entry */
> >    popl    %esi
> > 
> >    call    prot_to_real
> >    .code16
> > +
> > +    push    %dx
> > +    call    hex_out
> > +    push    %di
> > +    call    hex_out
> > +
> >    ljmp    $0, $GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR
> > +
> > +hex_out:
> > +    pushw    %bp
> > +    movw    %sp, %bp
> > +    pushaw
> > +    movb    $0xE, %ah
> > +    movw    $7, %bx
> > +    movw    $4, %cx
> > +    movw    4(%bp), %dx
> > +1:
> > +    rol    $4, %dx
> > +    movb    %dl, %al
> > +    andb    $0xF, %al
> > +    cmpb    $10, %al
> > +    jb    2f
> > +    subb    $('0'-'A'+10), %al
> > +2:
> > +    addb    $'0', %al
> > +    int    $0x10
> > +    loop    1b
> > +    movb    $' ', %al
> > +    int    $0x10
> > +    popaw
> > +    popw    %bp
> > +    ret    $2
> >    .code32
> > 
> > #include "../loader.S"
> > 
> > Perhaps you can try:
> > 
> > 1, %edi is used as backup register in case %edx is changed by
> > prot_to_real, you can remove "movl %edx, %edi", "push %di", "call
> > hex_out" and see if it still works.
> > 
> > 2, It's possible that the bug is position related, replace "push %dx",
> > "call hex_out" with equal number of nop and see what happens.
> > 
> > -- 
> > Bean
> > 
> 
> We can remove the patch completely, without putting nop also, but just 
> comment 
> out the following code
> 
> /*
>     xorl    %eax, %eax
>     call    EXT_C(grub_gate_a20)
> */
> 
> This is the only difference and when I comment out this, Windows boots up 
> from 
> Grub2.
> 
> Regards,
> Viswesh
> 
> 

So is this a bug in grub2 ?

Can you people confirm this ?

Viswesh



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