linux-kernel - Re: Patch "i386: Relocatable kernel support" causes instant reboot

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Date:	Thu, 21 Dec 2006 09:24:58 +0530
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Jean Delvare <khali@...ux-fr.org>, Andi Kleen <ak@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Patch "i386: Relocatable kernel support" causes instant reboot

On Thu, Dec 21, 2006 at 07:56:01AM +0530, Vivek Goyal wrote:
[..]
> >  #      Manual, Mixing 16-bit and 32-bit code, page 16-6)
> > 
> >         .byte 0x66, 0xea                        # prefix + jmpi-opcode
> > -code32:        .long   0x1000                          # will be set to 0x100000
> > -                                               # for big kernels
> > +code32:        .long   startup_32                      # will be set to %cs+startup_32
> >         .word   __BOOT_CS
> > +.code32
> > +startup_32:
> > +       movl $(__BOOT_DS), %eax
> > +       movl %eax, %ds
> > +       movl %eax, %es
> > +       movl %eax, %fs
> > +       movl %eax, %gs
> > +       movl %eax, %ss
> > +
> > +       xorl %eax, %eax
> > +1:     incl %eax                               # check that A20 really IS enabled
> > +       movl %eax, 0x00000000                   # loop forever if it isn't
> > +       cmpl %eax, 0x00100000
> > +       je 1b
> > +
> > +       # Jump to the 32bit entry point
> > +       jmpl *(code32_start - start + (DELTA_INITSEG << 4))(%esi)
> 
> Hi Eric,
> 
> I got a basic query. Why have we introduced this additional jump to 
> startup_32 in the same file? Won't it work if we stick to old method of
> enabling protected mode and then directly taking a jmp to startup_32 in
> arch/i386/kernel/head.S. Am I missing something obivious? 
> 

Sorry, I meant arch/i386/boot/compressed/head.S and not arch/i386/kernel/head.S

Thanks
Vivek
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