Re: [gentoo-user] OT: Can QEMU emulate cpu instructions the host cpu doesn't have?

[Poison BL.]

On Tue, Dec 20, 2016 at 8:12 PM, Walter Dnes <waltdnes@××××××××.org> wrote:

>   I have "Intel(R) Core(TM) i5-3330 CPU @ 3.00GHz" on a physical host
> machine.  I'd like to emulate a cpu with the "movbe" instruction set.
> Doing some testing, I tried, as root stuff like...
>
> qemu-system-x86_64 -enable-kvm -cpu Broadwell
>
> ...and got the following warnings
> warning: host doesn't support requested feature: CPUID.01H:ECX.fma [bit 12]
> warning: host doesn't support requested feature: CPUID.01H:ECX.movbe [bit
> 22]
> warning: host doesn't support requested feature: CPUID.07H:EBX.bmi1 [bit 3]
> warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
> warning: host doesn't support requested feature: CPUID.07H:EBX.avx2 [bit 5]
> warning: host doesn't support requested feature: CPUID.07H:EBX.bmi2 [bit 8]
> warning: host doesn't support requested feature: CPUID.07H:EBX.invpcid
> [bit 10]
> warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
> warning: host doesn't support requested feature: CPUID.07H:EBX.rdseed [bit
> 18]
> warning: host doesn't support requested feature: CPUID.07H:EBX.adx [bit 19]
> warning: host doesn't support requested feature: CPUID.07H:EBX.smap [bit
> 20]
> warning: host doesn't support requested feature: CPUID.80000001H:ECX.abm
> [bit 5]
> warning: host doesn't support requested feature: CPUID.80000001H:ECX.3dnowprefetch
> [bit 8]
>
>   On real qemu sessions "grep movbe /proc/cpuinfo" doesn't get any hits.
> I hope I'm doing something wrong here, rather than qemu not being able
> to emulate a newer cpu.  Any ideas?
>
> --
> Walter Dnes <waltdnes@××××××××.org>
> I don't run "desktop environments"; I run useful applications
>
>
I think the issue is using KVM there. When you're emulating something
feature-different from the host cpu (or at least something that requires an
added feature), I suspect you're stuck with non-accelerated emulation (I'm
pretty sure the *old* acceleration kernel module is no longer maintained).
I know qemu can do full emulation of instruction sets that the host cpu
lacks because I've used it for arm... but I've never really toyed with
other x86 series features like that personally.

-- 
Poison [BLX]
Joshua M. Murphy