Subject: Re: [net-next PATCH 3/4] samples/bpf: add a README file to get users started

From: Daniel Borkmann <[email-masked]>
Date: Tue, 26 Apr 2016 13:44:06 +0200

On 04/26/2016 01:09 PM, Jesper Dangaard Brouer wrote:
> Getting started with using examples in samples/bpf/ is not
> straightforward.  There are several dependencies, and specific
> versions of these dependencies.
>
> Just compiling the example tool is also slightly obscure, e.g. one
> need to call make like:
>
>   make samples/bpf/
>
> Do notice the "/" slash after the directory name.
>
> Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
> ---
>   samples/bpf/README.rst |   67 ++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 67 insertions(+)
>   create mode 100644 samples/bpf/README.rst
>
> diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
> new file mode 100644
> index 000000000000..3e1ac05d8e7c
> --- /dev/null
> +++ b/samples/bpf/README.rst
> @@ -0,0 +1,67 @@
> +eBPF sample programs
> +====================
> +
> +This kernel samples/bpf directory contains a mini eBPF library, test
> +stubs, verifier test-suite and examples for using eBPF.
> +
> +Build dependencies
> +==================
> +
> +Compiling requires having installed:
> + * clang
> + * llvm >= version 3.7.0
> +
> +Note that LLVM's tool 'llc' must support target 'bpf', list with command::
> +
> + $ llc --version
> + LLVM (http://llvm.org/):
> +  LLVM version 3.x.y
> +  [...]
> +  Host CPU: xxx
> +
> +  Registered Targets:
> +    [...]
> +    bpf        - BPF (host endian)
> +    bpfeb      - BPF (big endian)
> +    bpfel      - BPF (little endian)
> +    [...]
> +
> +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 compiling goto kernel top level build directory and run make like::
> +
> + make samples/bpf/
> +
> +Do notice the "/" slash after the directory name.
> +
> +Manually compiling LLVM with 'bpf' support
> +------------------------------------------
> +
> +In some LLVM versions the BPF target were marked experimental.  To
> +compile LLVM manually and enable BPF target run (build dependencies
> +are cmake and gcc-c++)::
> +
> + $ git clone http://llvm.org/git/llvm.git
> + $ cd llvm
> + $ mkdir build; cd build
> + $ cmake .. -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=BPF
> + $ make

That's perhaps a bit misleading in the sense that when you clone the
tree from git, you'd nowadays invoke cmake normally with LLVM_TARGETS_TO_BUILD
instead of LLVM_EXPERIMENTAL_TARGETS_TO_BUILD for BPF, as BPF is not an
experimental target anymore. It's probably also recommended to clone
clang into tools/ dir as well under your llvm/ repo when you compile
from scratch anyways.

> +It is also possible to point make to the newly compile 'llc' command
> +via redefining LLC on the make command line::
> +
> + make samples/bpf/ LLC=~/git/llvm/build/bin/llc
> +
>