1eBPF sample programs
  2====================
  3
  4This directory contains a test stubs, verifier test-suite and examples
  5for using eBPF. The examples use libbpf from tools/lib/bpf.
  6
  7Build dependencies
  8==================
  9
 10Compiling requires having installed:
 11 * clang >= version 3.4.0
 12 * llvm >= version 3.7.1
 13
 14Note that LLVM's tool 'llc' must support target 'bpf', list version
 15and supported targets with command: ``llc --version``
 16
 17Clean and configuration
 18-----------------------
 19
 20It can be needed to clean tools, samples or kernel before trying new arch or
 21after some changes (on demand)::
 22
 23 make -C tools clean
 24 make -C samples/bpf clean
 25 make clean
 26
 27Configure kernel, defconfig for instance::
 28
 29 make defconfig
 30
 31Kernel headers
 32--------------
 33
 34There are usually dependencies to header files of the current kernel.
 35To avoid installing devel kernel headers system wide, as a normal
 36user, simply call::
 37
 38 make headers_install
 39
 40This will create a local "usr/include" directory in the git/build top
 41level directory, that the make system will automatically pick up first.
 42
 43Compiling
 44=========
 45
 46For building the BPF samples, issue the below command from the kernel
 47top level directory::
 48
 49 make M=samples/bpf
 50
 51It is also possible to call make from this directory.  This will just
 52hide the invocation of make as above.
 53
 54Manually compiling LLVM with 'bpf' support
 55------------------------------------------
 56
 57Since version 3.7.0, LLVM adds a proper LLVM backend target for the
 58BPF bytecode architecture.
 59
 60By default llvm will build all non-experimental backends including bpf.
 61To generate a smaller llc binary one can use::
 62
 63 -DLLVM_TARGETS_TO_BUILD="BPF"
 64
 65We recommend that developers who want the fastest incremental builds
 66use the Ninja build system, you can find it in your system's package
 67manager, usually the package is ninja or ninja-build.
 68
 69Quick sniplet for manually compiling LLVM and clang
 70(build dependencies are ninja, cmake and gcc-c++)::
 71
 72 $ git clone https://github.com/llvm/llvm-project.git
 73 $ mkdir -p llvm-project/llvm/build
 74 $ cd llvm-project/llvm/build
 75 $ cmake .. -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \
 76            -DLLVM_ENABLE_PROJECTS="clang"    \
 77            -DCMAKE_BUILD_TYPE=Release        \
 78            -DLLVM_BUILD_RUNTIME=OFF
 79 $ ninja
 80
 81It is also possible to point make to the newly compiled 'llc' or
 82'clang' command via redefining LLC or CLANG on the make command line::
 83
 84 make M=samples/bpf LLC=~/git/llvm-project/llvm/build/bin/llc CLANG=~/git/llvm-project/llvm/build/bin/clang
 85
 86Cross compiling samples
 87-----------------------
 88In order to cross-compile, say for arm64 targets, export CROSS_COMPILE and ARCH
 89environment variables before calling make. But do this before clean,
 90configuration and header install steps described above. This will direct make to
 91build samples for the cross target::
 92
 93 export ARCH=arm64
 94 export CROSS_COMPILE="aarch64-linux-gnu-"
 95
 96Headers can be also installed on RFS of target board if need to keep them in
 97sync (not necessarily and it creates a local "usr/include" directory also)::
 98
 99 make INSTALL_HDR_PATH=~/some_sysroot/usr headers_install
100
101Pointing LLC and CLANG is not necessarily if it's installed on HOST and have
102in its targets appropriate arm64 arch (usually it has several arches).
103Build samples::
104
105 make M=samples/bpf
106
107Or build samples with SYSROOT if some header or library is absent in toolchain,
108say libelf, providing address to file system containing headers and libs,
109can be RFS of target board::
110
111 make M=samples/bpf SYSROOT=~/some_sysroot