Re: [PATCH 1/2] i386: use better matching family/model/stepping for 'qemu64' CPU

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, May 07, 2021 at 02:36:49PM +0100, Daniel P. Berrangé wrote:
> The 'qemu64' CPUID currently reports 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!
> 
> It appears LLVM looks at the family/model/stepping, despite qemu64
> reporting it is 64-bit capable.
> 
> This patch changes 'qemu64' 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.
> 
> Closes https://gitlab.com/qemu-project/qemu/-/issues/191
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  hw/i386/pc.c      | 6 +++++-
>  target/i386/cpu.c | 6 +++---
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 364816efc9..35d7a8122a 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -96,7 +96,11 @@
>  #include "trace.h"
>  #include CONFIG_DEVICES
>  
> -GlobalProperty pc_compat_6_0[] = {};
> +GlobalProperty pc_compat_6_0[] = {
> +    { "qemu64" "-" TYPE_X86_CPU, "family", "6" },
> +    { "qemu64" "-" TYPE_X86_CPU, "model", "6" },
> +    { "qemu64" "-" TYPE_X86_CPU, "stepping", "3" },

I wish we could have done this using a new CPU model version, but
the new version wouldn't be very useful unless the default CPU
model version to CPU_VERSION_LATEST[1], so:

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

[1] We still can't do that without breaking libvirt expectations
    about machine types.

> +};
>  const size_t pc_compat_6_0_len = G_N_ELEMENTS(pc_compat_6_0);
>  
>  GlobalProperty pc_compat_5_2[] = {
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index ad99cad0e7..99caa3deae 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -1881,9 +1881,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
>          .name = "qemu64",
>          .level = 0xd,
>          .vendor = CPUID_VENDOR_AMD,
> -        .family = 6,
> -        .model = 6,
> -        .stepping = 3,
> +        .family = 15,
> +        .model = 107,
> +        .stepping = 1,
>          .features[FEAT_1_EDX] =
>              PPRO_FEATURES |
>              CPUID_MTRR | CPUID_CLFLUSH | CPUID_MCA |
> -- 
> 2.31.1
> 

-- 
Eduardo