On 12.11.2008, at 16:45, Anthony Liguori wrote:
Alexander Graf wrote:
Hi,
I was thinking a bit about cross vendor migration recently and
since we're doing open source development, I figured it might be a
good idea to talk to everyone about this.
So why are we having a problem?
In normal operation we don't. If we're running a 32-bit kernel, we
can use SYSENTER to jump from kernel<->userspace. If we're on a 64-
bit kernel with 64-bit userspace, every CPU supports SYSCALL. At
least Linux is being smart on this and does use exactly these two
capabilities in these two cases.
But if we're running in compat mode (64-bit kernel with 32-bit
userspace), things differ. Intel supports only SYSENTER here, while
AMD only supports SYSCALL. Both can still use int80.
Obviously we can trap-and-emulate but that would be slow in a
relatively fast past.
If we can do it without emulation, I'd greatly prefer it, as syscall/
sysenter emulation in the hypervisor most probably isn't exactly
fast ;-). And you don't really want to degrade performance just
because you're migrating (think flashplayer here). I guess Windows 64-
bit contains even more 32-bit parts.
I wonder if patching is an option?
Windows does have background daemons that check code in runtime and
compares that to checksums. So binary patching might break Windows
pretty easily. I'm really wondering why the CR8 patching still works -
maybe even that'll break with Windows 7.
Alex
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