Re: [PATCH v3 bpf-next 05/14] samples: bpf: makefile: use __LINUX_ARM_ARCH__ selector for arm

[Ivan Khoronzhuk]

On Mon, Sep 16, 2019 at 01:44:23PM -0700, Andrii Nakryiko wrote:
> On Mon, Sep 16, 2019 at 3:59 AM Ivan Khoronzhuk
> <ivan.khoronzhuk@xxxxxxxxxx> wrote:
> > For arm, -D__LINUX_ARM_ARCH__=X is min version used as instruction
> > set selector and is absolutely required while parsing some parts of
> > headers. It's present in KBUILD_CFLAGS but not in autoconf.h, so let's
> > retrieve it from and add to programs cflags. In another case errors
> > like "SMP is not supported" for armv7 and bunch of other errors are
> > issued resulting to incorrect final object.
> > ---
> >  samples/bpf/Makefile | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index 8ecc5d0c2d5b..d3c8db3df560 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -185,6 +185,16 @@ HOSTLDLIBS_map_perf_test   += -lrt
> >  HOSTLDLIBS_test_overhead       += -lrt
> >  HOSTLDLIBS_xdpsock             += -pthread
> >
> > +ifeq ($(ARCH), arm)
> > +# Strip all except -D__LINUX_ARM_ARCH__ option needed to handle linux
> > +# headers when arm instruction set identification is requested.
> > +ARM_ARCH_SELECTOR = $(shell echo "$(KBUILD_CFLAGS) " | \
> > +                   sed 's/[[:blank:]]/\n/g' | sed '/^-D__LINUX_ARM_ARCH__/!d')
>
> Does the following work exactly like that without shelling out (and
> being arguably simpler)?
>
> ARM_ARCH_SELECTOR = $(filter -D__LINUX_ARM_ARCH__%, $(KBUILD_CFLAGS))
>
> > +
> > +CLANG_EXTRA_CFLAGS := $(ARM_ARCH_SELECTOR)
> > +KBUILD_HOSTCFLAGS := $(ARM_ARCH_SELECTOR)
>
> Isn't this clearing out previous value of KBUILD_HOSTCFLAGS? Is that
> intentional, or it was supposed to be += here?
>
> > +endif
> > +
> >  # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
> >  #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> >  LLC ?= llc
> > --
> > 2.17.1

Just left from previous version filtering all -D options.
Will update in next v., SELECTOR also.

--
Regards,
Ivan Khoronzhuk