On 04/26/2016 01:56 PM, Jesper Dangaard Brouer wrote:
On Tue, 26 Apr 2016 13:44:06 +0200
Daniel Borkmann <daniel@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
---
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+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?
You mean how to build with clang? There are various docs/snippets out
there, for example, see the 'Build LLVM and Clang development libs'
part of [1], that you can tweak for your README with.
[1] https://gist.github.com/brendangregg/cfa482acb71aa577789c
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