Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Michal Marek]

On Mon, Jul 13, 2015 at 08:59:33PM +1000, Anton Blanchard wrote:
> Hi,
> 
> >      > When the host's C compiler is clang, and when attempting to
> >      > cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the
> >      > Makefile would incorrectly detect the use of clang, which
> >      > resulted in clang-specific flags being passed to
> >      > mipsel-linux-gcc.
> >      >
> >      > This can be verified under Debian by installing the "clang"
> >      > package, and then using it as the default compiler with:
> >      > sudo update-alternatives --config cc
> >      >
> >      > This patch moves the detection of clang after the $(CC)
> >      > variable is initialized to the name of the cross-compiler, so
> >      > that the check applies
> >      > to the cross-compiler and not the host's C compiler.
> >      >
> >      > v2: Move the detection of clang after the inclusion of the
> >      > arch/*/Makefile (as they might set $(CROSS_COMPILE))
> >      >
> >      > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx
> >     <mailto:paul@xxxxxxxxxxxxxxx>>
> > 
> >     Applied to kbuild.git#kbuild. I will push it after v4.1-rc1
> >     becomes available, though.
> > 
> > Drat. I wish I saw this earlier.
> > 
> > This breaks patches which check for the value of COMPILER in 
> > arch/*/Makefile. This detection must be performed before the
> > inclusion of the arch Makefile.
> > 
> > Can I move this to after the initialization of CC but before the
> > include?
> > 
> > I'm not sure that being able to define the default compiler per arch
> > is necessary. But I know I need to be able to add arch specific flags
> > for clang.
> 
> I can confirm the patch breaks ppc64le clang builds.

Can you try the (untested) patch below?