Re: [PATCH] selftests: propagate CC to selftest submakes

[Shuah Khan]

On 12/10/20 5:10 PM, Andrew Delgadillo wrote:
> On Thu, Dec 10, 2020 at 3:08 PM Nick Desaulniers
> <ndesaulniers@xxxxxxxxxx> wrote:
> > On Thu, Dec 3, 2020 at 2:10 PM Andrew Delgadillo <adelg@xxxxxxxxxx> wrote:
> > > lib.mk defaults to gcc when CC is not set. When building selftests
> > > as part of a kernel compilation, MAKEFLAGS is cleared to allow implicit
> > > build rules to be used. This has the side-effect of clearing the CC
> > > variable, which will cause selftests to be built with gcc regardless of
> > > if we are using gcc or clang. To remedy this, propagate the CC variable
> > > when clearing makeflags to ensure the correct compiler is used.
> > >
> > > Signed-off-by: Andrew Delgadillo <adelg@xxxxxxxxxx>
> >
> > Hi Andrew, thanks for the patch. Can you walk me through how to build
> > the selftests?
> >
> > Documentation/dev-tools/kselftest.rst says:
> > $ make -C tools/testing/selftests
> >
> > And if I do:
> > $ make CC=clang defconfig
> > $ make CC=clang -C tools/testing/selftests -j
> >
> > I observe a spew of errors.  If I apply your patch and rerun the
> > above, I see what looks like the same spew of errors.  Am I "holding
> > it wrong" or could the docs use a refresh?
>
> Hi Nick, sure thing!
>
> I also see a slew of errors when building with make -C
> tools/testing/selftests. However, that is not the problem I am trying
> to solve. I believe we are seeing errors building that way because it
> is missing some make variables that are normally set up when building
> from the kernel's top level makefile.

Both options are supported and should work.

make -C tools/testing/selftests
make kselftest

That being said, I use gcc. Can you send the errors you are seeing?
It is possible, a few tests aren't building and need to be fixed
for clang and gcc.

thanks,
-- Shuah