[PATCH bpf-next 11/11] samples: bpf: makefile: add sysroot support

[Ivan Khoronzhuk]

Basically it only enables that was added by previous couple fixes.
For sure, just make tools/include to be included after sysroot
headers.

export ARCH=arm
export CROSS_COMPILE=arm-linux-gnueabihf-
make samples/bpf/ SYSROOT="path/to/sysroot"

Sysroot contains correct libs installed and its headers ofc.
Useful when working with NFC or virtual machine.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 samples/bpf/Makefile   |  5 +++++
 samples/bpf/README.rst | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 4edc5232cfc1..68ba78d1dbbe 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -177,6 +177,11 @@ ifeq ($(ARCH), arm)
 CLANG_EXTRA_CFLAGS := $(D_OPTIONS)
 endif
 
+ifdef SYSROOT
+ccflags-y += --sysroot=${SYSROOT}
+PROGS_LDFLAGS := -L${SYSROOT}/usr/lib
+endif
+
 ccflags-y += -I$(objtree)/usr/include
 ccflags-y += -I$(srctree)/tools/lib/bpf/
 ccflags-y += -I$(srctree)/tools/testing/selftests/bpf/
diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
index 5f27e4faca50..786d0ab98e8a 100644
--- a/samples/bpf/README.rst
+++ b/samples/bpf/README.rst
@@ -74,3 +74,13 @@ samples for the cross target.
 export ARCH=arm64
 export CROSS_COMPILE="aarch64-linux-gnu-"
 make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
+
+If need to use environment of target board (headers and libs), the SYSROOT
+also can be set, pointing on FS of target board:
+
+export ARCH=arm64
+export CROSS_COMPILE="aarch64-linux-gnu-"
+make samples/bpf/ SYSROOT=~/some_sdk/linux-devkit/sysroots/aarch64-linux-gnu
+
+Setting LLC and CLANG is not necessarily if it's installed on HOST and have
+in its targets appropriate arch triple (usually it has several arches).
-- 
2.17.1