On Sat, Nov 14, 2009 at 04:38:22PM +0100, Robert Millan wrote:
> > Following code can check A20:
> > *((volatile grub_uint8_t *) 0x200000) = 0;
> > *((volatile grub_uint8_t *) 0x300000) = 1;
> > if (*((volatile grub_uint8_t *) 0x200000))
> > grub_printf ("Expect bugs\n");
> > else
> > grub_printf ("You're safe\n");
>
> Yeah, in fact we have gate_a20_check_state() to check for this, but only
> in i386-pc.
>
> I find it surprising that i386-qemu works at all without it. I guess it
> only works because the high mem area that would overlap with our code in
> 0x8200 is never used.
>
> I'll look into this...
It appears that QEMU hardware already starts with A20 enabled. I suppose it's
bochsbios who disables it. In any case, I made my vbe-on-coreboot branch
enable it.
Unfortunately, this wasn't the cause that prevented vbetest/vbeinfo from
working :-/
--
Robert Millan
The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
how) you may access your data; but nobody's threatening your freedom: we
still allow you to remove your data and not access it at all."
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