Re: [PATCH bpf-next 05/11] samples: bpf: makefile: use D vars from KBUILD_CFLAGS to handle headers

[Ivan Khoronzhuk]

On Fri, Sep 13, 2019 at 09:12:01PM +0000, Yonghong Song wrote:
> On 9/10/19 11:38 AM, Ivan Khoronzhuk wrote:
> > The kernel headers are reused from samples bpf, and autoconf.h is not
> > enough to reflect complete arch configuration for clang. But CLANG-bpf
> > cmds are sensitive for assembler part taken from linux headers and -D
> > vars, usually used in CFLAGS, should be carefully added for each arch.
> > For that, for CLANG-bpf, lets filter them only for arm arch as it
> > definitely requires __LINUX_ARM_ARCH__ to be set, but ignore for
> > others till it's really needed. For arm, -D__LINUX_ARM_ARCH__ is min
> > version used as instruction set selector. In another case errors
> > like "SMP is not supported" for arm and bunch of other errors are
> > issued resulting to incorrect final object.
> >
> > Later D_OPTIONS can be used for gcc part.
> > ---
> >   samples/bpf/Makefile | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index 8ecc5d0c2d5b..6492b7e65c08 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -185,6 +185,15 @@ HOSTLDLIBS_map_perf_test	+= -lrt
> >   HOSTLDLIBS_test_overhead	+= -lrt
> >   HOSTLDLIBS_xdpsock		+= -pthread
> >
> > +# Strip all expet -D options needed to handle linux headers
> > +# for arm it's __LINUX_ARM_ARCH__ and potentially others fork vars
> > +D_OPTIONS = $(shell echo "$(KBUILD_CFLAGS) " | sed 's/[[:blank:]]/\n/g' | \
> > +	sed '/^-D/!d' | tr '\n' ' ')
> > +
> > +ifeq ($(ARCH), arm)
> > +CLANG_EXTRA_CFLAGS := $(D_OPTIONS)
> > +endif
>
> Do you need this for native compilation?
Yes, native "arm" also requires it.

> so arm64 compilation does not need this?
yes, now only arm

> If only -D__LINUX_ARM_ARCH__ is needed, maybe just
> with
>    CLANG_EXTRA_CFLAGS := -D__LINUX_ARM_ARCH__
Value also needed: -D__LINUX_ARM_ARCH_=7 or -D__LINUX_ARM_ARCH_=6
So, need retrieve it.

> Otherwise, people will wonder whether this is needed for
> other architectures. Or just do
>    CLANG_EXTRA_CFLAGS := $(D_OPTIONS)
> for all cross compilation?
arm, cross and native requires it.

Will do this:

# Strip all expet -D options needed to handle linux headers
# for arm it's __LINUX_ARM_ARCH__ and potentially others fork vars
ifeq ($(ARCH), arm)
D_OPTIONS = $(shell echo "$(KBUILD_CFLAGS) " | sed 's/[[:blank:]]/\n/g' | \
	sed '/^-D/!d' | tr '\n' ' ')
endif

CLANG_EXTRA_CFLAGS := $(D_OPTIONS)



> > +
> >   # 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

--
Regards,
Ivan Khoronzhuk