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Date: Wed, 22 Jan 2003 11:56:41 -0800
From: Andrew Morton <akpm@digeo.com>
To: Kevin Lawton <kevinlawton2001@yahoo.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Simple patches for Linux as a guest OS in a plex86 VM (please
 consider)
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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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