Re: [PATCH v2 1/2] selftests/lib.mk: handle both LLVM=1 and CC=clang builds

[John Hubbard]

On 6/3/24 10:09 AM, John Hubbard wrote:
> On 6/3/24 8:32 AM, Mark Brown wrote:
> > On Fri, May 31, 2024 at 11:37:50AM -0700, John Hubbard wrote:
> > > The kselftests may be built in a couple different ways:
> > >      make LLVM=1
> > >      make CC=clang
> > >
> > > In order to handle both cases, set LLVM=1 if CC=clang. That way,the rest
> > > of lib.mk, and any Makefiles that include lib.mk, can base decisions
> > > solely on whether or not LLVM is set.
> >
> > ICBW but I believe there are still some architectures with clang but not
> > lld support where there's a use case for using CC=clang.
>
> I'm inclined to wait for those to make themselves known... :)

...but thinking about this some more, maybe this patch is actually
a Bad Idea. Because it is encouraging weirdness and divergence from
how kbuild does it. And kbuild is very clear [1]:


Building with LLVM

Invoke make via:

make LLVM=1

to compile for the host target. For cross compiling:

make LLVM=1 ARCH=arm64

The LLVM= argument

LLVM has substitutes for GNU binutils utilities. They can be enabled individually. The full list of supported make variables:

make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \
  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
  HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld

LLVM=1 expands to the above.

[1] https://docs.kernel.org/kbuild/llvm.html

thanks,
--
John Hubbard
NVIDIA