bpf

eBPF sample programs

This directory contains a test stubs, verifier test-suite and examples for using eBPF. The examples use libbpf from tools/lib/bpf.

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

Cross compiling samples

In order to cross-compile, say for arm64 targets, export CROSS_COMPILE and ARCH environment variables before calling make. This will direct make to build 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