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SubjectRe: Simple patches for Linux as a guest OS in a plex86 VM (please consider)
Kevin Lawton <kevinlawton2001@yahoo.com> wrote:
>
> Hello all,
>
> I'm working on running Linux as a guest OS inside a
> lightweight cut-down plex86 environment. My goal is to
> run a stock Linux kernel, which can be slimmed down to
> the essentials via kernel configuration, since a guest
> OS doesn't need to drive much hardware.
>
> For this, there's a few critical but simple diffs to
> macro'ize the use of the PUSHF and POPF instructions,
> due to broken semantics of running stuff using
> PVI (protected mode virtual interrupts). The rest of
> the stuff I believe can be monitored effectively by
> the VM monitor.
>
> Would you please consider integrating these diffs before 2.6?
> There's only one new header file, and macro substitution for
> a few cases where these instructions are used. For a normal
> compile, there are zero logic changes. Just 1:1 macros.

I'm wondering if this can this be done a lot more simply with assembler
macros.

The below example generates the right code. It's then just a matter of
getting the redefined pushfl and popfl macros into kernel-wide scope.
Possibly an explicit `-include' in the makefile system.


asm("
.macro popfl
testl $(1<<9), 0(%esp)
jz 69003f
.byte 0x9d # popfl
sti
jmp 69004f
69003:
.byte 0x9d # popfl
cli
69004:
.endm
");

foo()
{
asm("popfl\n");
}

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