Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

Eric W. Biederman
2006-10-06T19:03:24Z

Vivek Goyal <vgoyal@in.ibm.com> writes:

> Hi Eric,
>
> I have added cld in the regenerated patch below.
>
> Also one more minor nit. stosb relies on being %es set properly. By the
> time control reaches loader_ok, i could not find %es being set explicitly
> hence I am assuming we are relying on bootloader to set it up for us.

No my bad. I was thinking it was %ds, like everything else.

> Maybe we can be little more paranoid and setup the %es before stosb. I
> have done this change too in the attached patch. Pleaese have a look.
> I know little about assembly code.

Looks good to me.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

> In the lazy programmer school of fixes.
>
> I haven't really tested this in any configuration.
> But reading video.S it does use variable in the bootsector.
> It does seem to initialize the variables before use.
> But obviously something is missed.
>
> By zeroing the uninteresting parts of the bootsector just after we
> have determined we are loaded ok. We should ensure we are
> always in a known state the entire time.
>
> Andrew if I am right about the cause of your video not working
> when you set an enhanced video mode this should fix your boot
> problem.
>
> Singed-off-by: Eric Biederman <ebiederm@xmission.com>
>
> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
> ---
>
> arch/i386/boot/setup.S | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff -puN arch/i386/boot/setup.S~i386-set-bootset-to-zero-fix
> arch/i386/boot/setup.S
> --- linux-2.6.18-git17/arch/i386/boot/setup.S~i386-set-bootset-to-zero-fix
> 2006-10-06 12:42:19.000000000 -0400
> +++ linux-2.6.18-git17-root/arch/i386/boot/setup.S 2006-10-06 12:49:37.000000000
> -0400
> @@ -287,6 +287,17 @@ good_sig:
> loader_panic_mess: .string "Wrong loader, giving up..."
>
> loader_ok:
> +# Zero initialize the variables we keep in the bootsector
> + movw %cs, %ax # aka SETUPSEG
> + subw $DELTA_INITSEG, %ax # aka INITSEG
> + movw %ax, %es
> + xorw %di, %di
> + xorb %al, %al
> + movw $497, %cx
> + cld
> + rep
> + stosb
> +
> # Get memory size (extended mem, kB)
>
> xorl %eax, %eax
> _