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[prefix] Use 16-bit protected mode for access to high memory

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Flat real mode works perfectly on real hardware, but seems to cause
problems for some hypervisors.  Revert to using 16-bit protected mode
(and returning to real mode with 4GB limits, so as not to break PMM
BIOSes).

Allow the code specific to the .mrom format to continue to assume that
flat real mode works, since this format is specific to real hardware.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2011-01-26 23:04:43 +00:00
parent 21d6f9cd8e
commit a84e15234a
2 changed files with 196 additions and 43 deletions
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7
src/arch/i386/prefix/mromprefix.S
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@@ -151,7 +151,12 @@ find_mem_bar:
/* Copy payload to buffer, or set buffer address to BAR address */
testl %esi, %esi
jz 1f
/* We have a buffer; copy payload to it */
/* We have a buffer; copy payload to it. Since .mrom is
* designed specifically for real hardware, we assume that
* flat real mode is working properly. (In the unlikely event
* that this code is run inside a hypervisor that doesn't
* properly support flat real mode, it will die horribly.)
*/
pushl %esi
pushw %es
movl %esi, %edi