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Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2

From: Anthony Liguori
Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?
Date: Wed, 04 Aug 2010 10:07:24 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Lightning/1.0b1 Thunderbird/3.0.6

On 08/04/2010 10:01 AM, Gleb Natapov wrote:

Hm, may be. I read seabios code differently, but may be I misread it.

The BIOS Boot Specification spells it all out pretty clearly.

If a ROM needs memory after the init function, it needs to use the
traditional tricks to allocate long term memory and the most popular
one is modifying the e820 tables.

e820 has no in memory format,


See src/arch/i386/firmware/pcbios/e820mangler.S in gPXE.
so this ugly code intercepts int15 and mangle result. OMG. How this can
even work if more then two ROMs want to do that?

You have to save the old handlers and invoke them. Where do you save the old handlers? There's tricks you can do by trying to use some unused vectors and also temporarily using the stack.

But basically, yeah, I'm amazed every time I see a PC boot that it all actually works :-)


Anthony Liguori


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