Re: [PATCH 0/2] i386: use better matching family/model/stepping for generic CPUs

[Daniel P . Berrangé]

ping

On Fri, May 07, 2021 at 02:36:48PM +0100, Daniel P. Berrangé wrote:
> This is in response to this bug report:
> 
>    https://gitlab.com/qemu-project/qemu/-/issues/191
> 
> The generic 'qemu64' and 'max' CPUs currently defined to report a
> family/model/stepping that approximately corresponds to an AMD K7
> vintage architecture. The K7 series predates the introduction of
> 64-bit support by AMD in the K8 series. This has been reported to
> lead to LLVM complaints about generating 64-bit code for a 32-bit
> CPU target
> 
>   LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
> 
> The bug report is fairly limited, but it suggests LLVM looks at the
> family/model/stepping and decides it to be 32-bit, despite qemu64
> reporting it is 64-bit capable. I've not reproduced this myself,
> however, so I'm largely trusting the original reporter's diagnosis
> 
> Of course interpreting the family/model/stepping only makes sense
> with scoped to the reported vendor ID.  Under TCG, the vendor is
> honoured, but AFAICT, under KVM the vendor defined by the QEMU
> model model is ignored and the real host vendor passed through.
> This will make the chosen family/model/stepping non-sensical when
> run under KVM on an Intel host.
> 
> None the less these patches change to report a CPUID with the
> family, model and stepping taken from a
> 
>  AMD Athlon(tm) 64 X2 Dual Core Processor 4000+
> 
> which is one of the first 64-bit AMD CPUs. This is at least more
> accurate in terms of the static CPU model definition, even if it
> is still nonsense in the case where KVM overrides the vendor to
> be non-AMD.
> 
> Daniel P. Berrangé (2):
>   i386: use better matching family/model/stepping for 'qemu64' CPU
>   i386: use better matching family/model/stepping for 'max' CPU
> 
>  hw/i386/pc.c      |  6 +++++-
>  target/i386/cpu.c | 12 +++++++++---
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> -- 
> 2.31.1
> 
> 

Regards,
Daniel
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