[PATCH RFC bpf-next 05/10] samples: bpf: Makefile: use vars from KBUILD_CFLAGS to handle linux headers

[Ivan Khoronzhuk]

The kernel headers are reused from samples bpf, and autoconf.h is not
enough to reflect complete configuration for clang. One of such
configurations is __LINUX_ARM_ARCH__ min version used as instruction
set selector. In another case an error like "SMP is not
supported" for arm and others errors are issued and final object is
not correct.
---
 samples/bpf/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index cdd742c05200..9232efa2b1b3 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -186,6 +186,13 @@ 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' ' ')
+
+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
-- 
2.17.1