Re: [PATCH 06/14] KVM: selftests: Rename UNAME_M to ARCH_DIR, fill explicitly for x86

[Sean Christopherson]

+David

On Tue, Dec 13, 2022, Sean Christopherson wrote:
> Rename UNAME_M to ARCH_DIR and explicitly set it directly for x86.  At
> this point, the name of the arch directory really doesn't have anything
> to do with `uname -m`, and UNAME_M is unnecessarily confusing given that
> its purpose is purely to identify the arch specific directory.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> -# No change necessary for x86_64
> -UNAME_M := $(shell uname -m)
> -
> -# Set UNAME_M for arm64 compile/install to work
> -ifeq ($(ARCH),arm64)
> -	UNAME_M := aarch64
> -endif
> -# Set UNAME_M s390x compile/install to work
> -ifeq ($(ARCH),s390)
> -	UNAME_M := s390x
> -endif
> -# Set UNAME_M riscv compile/install to work
> -ifeq ($(ARCH),riscv)
> -	UNAME_M := riscv
> +ifeq ($(ARCH),x86)

As discovered by by David, this breaks doing "ARCH=x86_64 make", which is an
allowed/supported variant in the kernel proper, so this needs to be:

  ifneq (,$(filter $(ARCH),x86 x86_64))

or alternatively

  ifeq ($(ARCH),x86_64)
  ARCH := x86
  endif

Hmm, unless there's a reason to keep ARCH=x86_64, the latter appears to be the
better option as lib.mak doesn't play nice with x86_64 either, e.g. `ARCH=x86_64
LLVM=1 make` fails.  That's arguably a lib.mak bug, but it's trivial to handle
in KVM's makefile so forcing lib.mak to handle both seems unnecessary.

I'll also add a comment to call out that $(ARCH) follows the kernel's terminology
for arch/*, whereas for whatever reason KVM selftests effectively uses `uname -m`
terminology.

One last thought/question, what do y'all think about renaming directories to
follow the kernel proper?  I.e. aarch64=>arm64, s390x=>s390, and x86_64=>x86.
Then $(ARCH_DIR) would go away.  The churn would be unfortunate, but it would be
nice to align with arch/ and tools/arch/.

> +	ARCH_DIR := x86_64
> +else ifeq ($(ARCH),arm64)
> +	ARCH_DIR := aarch64
> +else ifeq ($(ARCH),s390)
> +	ARCH_DIR := s390x
> +else ifeq ($(ARCH),riscv)
> +	ARCH_DIR := riscv
> +else
> +$(error Unknown architecture '$(ARCH)')
>  endif