Re: [PATCH 2/6] meson: assume x86-64-v2 baseline ISA

[Zhao Liu]

On Fri, May 31, 2024 at 11:14:53AM +0200, Paolo Bonzini wrote:
> Date: Fri, 31 May 2024 11:14:53 +0200
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH 2/6] meson: assume x86-64-v2 baseline ISA
> X-Mailer: git-send-email 2.45.1
> 
> x86-64-v2 processors were released in 2008, assume that we have one.
> Unfortunately there is no GCC flag to enable all the features
> without disabling what came after; so enable them one by one.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  meson.build | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index 63866071445..19d1fc1f33b 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -336,9 +336,13 @@ if host_arch == 'i386' and not cc.links('''
>    qemu_common_flags = ['-march=i486'] + qemu_common_flags
>  endif
>  
> -# ??? Only extremely old AMD cpus do not have cmpxchg16b.
> -# If we truly care, we should simply detect this case at
> -# runtime and generate the fallback to serial emulation.
> +# Assume x86-64-v2 (minus CMPXCHG16B for 32-bit code)

Is it necessary to state the requirement (x86-64-v2) for x86 host in
some doc?

e.g., docs/system/target-i386.rst.

> +if host_arch == 'i386'
> +  qemu_common_flags = ['-mfpmath=sse'] + qemu_common_flags
> +endif
> +if host_arch in ['i386', 'x86_64']
> +  qemu_common_flags = ['-mpopcnt', '-msse4.2'] + qemu_common_flags
> +endif
>  if host_arch == 'x86_64'
>    qemu_common_flags = ['-mcx16'] + qemu_common_flags
>  endif
> -- 
> 2.45.1

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>