Merge branch 'samples-bpf-user-experience'

HOSTLOADLIBES_map_perf_test += -lelf -lrt

HOSTLOADLIBES_test_overhead += -lelf -lrt

# 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

CLANG ?= clang

# Trick to allow make to be run from this directory

all:

	$(MAKE) -C ../../ $$PWD/

clean:

	$(MAKE) -C ../../ M=$$PWD clean

	@rm -f *~

# Verify LLVM compiler tools are available and bpf target is supported by llc

.PHONY: verify_cmds verify_target_bpf $(CLANG) $(LLC)

verify_cmds: $(CLANG) $(LLC)

	@for TOOL in $^ ; do \

		if ! (which -- "$${TOOL}" > /dev/null 2>&1); then \

			echo "*** ERROR: Cannot find LLVM tool $${TOOL}" ;\

			exit 1; \

		else true; fi; \

	done

verify_target_bpf: verify_cmds

	@if ! (${LLC} -march=bpf -mattr=help > /dev/null 2>&1); then \

		echo "*** ERROR: LLVM (${LLC}) does not support 'bpf' target" ;\

		echo "   NOTICE: LLVM version >= 3.7.1 required" ;\

		exit 2; \

	else true; fi

$(src)/*.c: verify_target_bpf

# asm/sysreg.h - inline assembly used by it is incompatible with llvm.

# But, there is no easy way to fix it, so just exclude it since it is

# useless for BPF samples.

$(obj)/%.o: $(src)/%.c

	clang $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \

	$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \

		-D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \

		-O2 -emit-llvm -c $< -o -| llc -march=bpf -filetype=obj -o $@

		-O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf -filetype=obj -o $@

eBPF sample programs

====================

This directory contains a mini eBPF library, test stubs, verifier

test-suite and examples for using eBPF.

Build dependencies

==================

Compiling requires having installed:

 * clang >= version 3.4.0

 * llvm >= version 3.7.1

Note that LLVM's tool 'llc' must support target 'bpf', list version

and supported targets with command: ``llc --version``

Kernel headers

--------------

There are usually dependencies to header files of the current kernel.

To avoid installing devel kernel headers system wide, as a normal

user, simply call::

 make headers_install

This will creates a local "usr/include" directory in the git/build top

level directory, that the make system automatically pickup first.

Compiling

=========

For building the BPF samples, issue the below command from the kernel

top level directory::

 make samples/bpf/

Do notice the "/" slash after the directory name.

It is also possible to call make from this directory.  This will just

hide the the invocation of make as above with the appended "/".

Manually compiling LLVM with 'bpf' support

------------------------------------------

Since version 3.7.0, LLVM adds a proper LLVM backend target for the

BPF bytecode architecture.

By default llvm will build all non-experimental backends including bpf.

To generate a smaller llc binary one can use::

 -DLLVM_TARGETS_TO_BUILD="BPF"

Quick sniplet for manually compiling LLVM and clang

(build dependencies are cmake and gcc-c++)::

 $ git clone http://llvm.org/git/llvm.git

 $ cd llvm/tools

 $ git clone --depth 1 http://llvm.org/git/clang.git

 $ cd ..; mkdir build; cd build

 $ cmake .. -DLLVM_TARGETS_TO_BUILD="BPF;X86"

 $ make -j $(getconf _NPROCESSORS_ONLN)

It is also possible to point make to the newly compiled 'llc' or

'clang' command via redefining LLC or CLANG on the make command line::

 make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang