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

[Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>]

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
+
 # 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