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

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Date:	Tue, 26 Apr 2016 13:56:47 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	netdev@...r.kernel.org, bblanco@...mgrid.com,
	borkmann@...earbox.net, alexei.starovoitov@...il.com,
	linux-kbuild@...r.kernel.org, brouer@...hat.com
Subject: Re: [net-next PATCH 3/4] samples/bpf: add a README file to get
 users started

On Tue, 26 Apr 2016 13:44:06 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:

> 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 <brouer@...hat.com>
> > ---
> >   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.

Can you come up with a formulation/desc I can use instead then?

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer