Re: [ kvm-Bugs-1807620 ] KVM's --disable-gcc-check doesn't work

Bernhard Kaindl
2007-10-05T16:54:06Z

On Thu, 4 Oct 2007, Gregory Haskins wrote:
> On Thu, 2007-10-04 at 19:27 +0200, Farkas Levente wrote:
>
>> ok but now as qemu code was imported into kvm, then it's probably would
>> be better to witch gcc-4.x?
>
> Sure. Are you volunteering? ;) I'm sure both upstream QEMU developers,
> KVM developers, and the community using either would be most
> appreciative. I know I would be.

Here is a discussion thread about a patch by Michael Matz to make qemu's
CPU emulation code actually work with gcc4:

http://www.nabble.com/-patch--make-qemu-work-with-GCC-4-t4345765.html

It's against the current qemu CVS, so as Avi updated kvm to qemu CVS now,
it might be worth a try.

It means that the CPU emulation incurs a 3% performance regression, but
the CPU emulation is only used when the CPU is not emulated by KVM in
the kernel, so it should be a not a big concern for KVM, and if gcc4
would compile more efficent code for the device emulatoin, it could
even lead to a theoritical speedup when KVM does CPU emulation, but
that is a pure theory.

In this mail (which you do not see in the above thread view), a
git repository with cumulated changes for qemu with gcc4 is mentioned,
it seems to have further fixes on top of the initial patch:

http://www.mail-archive.com/qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org/msg12017.html

Bernhard Kaindl