p4c

p4c is a new, alpha-quality reference compiler for the P4 programming language. It supports both P4-14 and P4-16; you can find more information about P4 here and the specifications for both versions of the language here.

p4c is modular; it provides a standard frontend and midend which can be combined with a target-specific backend to create a complete P4 compiler. The goal is to make adding new backends easy.

The code contains three sample backends:

• p4c-bm2-ss: can be used to target the P4 simple_switch written using the BMv2 behavioral model https://github.com/p4lang/behavioral-model
• p4c-ebpf: can be used to generate C code which can be compiled to EBPF https://en.wikipedia.org/wiki/Berkeley_Packet_Filter and then loaded in the Linux kernel for packet filtering
• p4test: a source-to-source P4 translator which can be used for testing, learning compiler internals and debugging.

Getting started

1. Clone the repository. It includes submodules, so be sure to use --recursive to pull them in:

   git clone --recursive https://github.com/p4lang/p4c.git
   

   If you forgot --recursive, you can update the submodules at any time using:

   git submodule update --init --recursive
   

2. Install dependencies. You can find specific instructions for Ubuntu 16.04 here and for macOS 10.12 here.

3. Build. By default, building takes place in a subdirectory named build.

   ./bootstrap.sh
   cd build
   make -j4
   make check -j4
   

4. (Optional) Install the compiler and the P4 shared headers globally.

   sudo make install
   

   The compiler driver p4c and binaries for each of the backends are installed in /usr/local/bin by default; the P4 headers are placed in /usr/local/share/p4c.

5. You're ready to go! You should be able to compile a P4-16 program for BMV2 using:

   p4c -b bmv2-v1model-p4org program.p4 -o program.bmv2.json
   

If you plan to contribute to p4c, you'll find more useful information here.

Dependencies

Ubuntu 16.04 is the officially supported platform for p4c. There's also unofficial support for macOS 10.12. Other platforms are untested; you can try to use them, but YMMV.

• A C++11 compiler. GCC 4.9 or later or Clang 3.3 or later is required.

• git for version control

• GNU autotools for the build process

• Boehm-Weiser garbage-collector C++ library

• GNU Bison and Flex for the parser and lexical analyzer generators.

• Google Protocol Buffers 3.0 for control plane API generation

• GNU multiple precision library GMP

• C++ boost library (minimally used)

• Python 2.7 for scripting and running tests

• Optional: Documentation generation (enabled when configuring with --enable-doxygen-doc) requires Doxygen (1.8.10 or higher) and Graphviz (2.38.0 or higher).

Backends may have additional dependencies. The dependencies for the backends included with p4c are documented here:

• BMv2
• eBPF

Ubuntu dependencies

Most dependencies can be installed using apt-get install:

sudo apt-get install g++ git automake libtool libgc-dev bison flex libfl-dev libgmp-dev libboost-dev libboost-iostreams-dev pkg-config python python-scapy python-ipaddr tcpdump

For documentation building: sudo apt-get install -y doxygen graphviz texlive-full

An exception is Google Protocol Buffers; p4c depends on version 3.0, which is not available until Ubuntu 16.10. For earlier releases of Ubuntu, you'll need to install from source. You can find instructions here. Check out the newest tag in the 3.0 series (v3.0.2 as of this writing) before you build.

git checkout v3.0.2

Please note that while newer versions should work for p4c itself, you may run into trouble with some extensions unless you install version 3.0, so you may want to install from source even on newer releases of Ubuntu.

macOS dependencies

Installing on macOS:

• Enable XCode's command-line tools:

  xcode-select --install
  

• Install Homebrew:

  /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
  

  Be sure to add /usr/local/bin/ to your $PATH.

• Install dependencies using Homebrew:

  brew install autoconf automake libtool bdw-gc boost bison pkg-config
  

  Install GMP built in C++11 mode:

  brew install gmp --c++11
  

  By default, Homebrew doesn't link programs into /usr/local/bin if they would conflict with a version provided by the base system. This includes Bison, since an older version ships with macOS. make check depends on the newer Bison we just installed from Homebrew (see #83), so you'll want to add it to your $PATH one way or another. One simple way to do that is to request that Homebrew link it into /usr/local/bin:

  brew link --force bison
  

  Optional documentation building tools:

  brew install doxygen graphviz
  

  Homebrew offers a protobuf formula. It installs version 3.2, which should work for p4c itself but may cause problems with some extensions. It's preferable to install Protocol Buffers 3.0 from source using the instructions here. Check out the newest tag in the 3.0 series (v3.0.2 as of this writing) before you build.

Development tools

There is a variety of design and development documentation here.

We recommend using clang++ with no optimizations for speeding up compilation and simplifying debugging.

We recommend installing a new version of gdb., because older gdb versions do not always handle C++11 correctly.

We recommend exuberant ctags for navigating source code in Emacs and vi. sudo apt-get install exuberant-ctags. The Makefile targets make ctags and make etags generate tags for vi and Emacs respectively. (Make sure that you are using the correct version of ctags; there are several competing programs with the same name in existence.)

To enable building code documentation, please run bootstrap.sh --enable-doxygen-doc. This enables the make docs rule to generate documentation. The HTML output is available in build/doxygen-out/html/index.html.

Docker

A Dockerfile is included. You can generate an image which contains a copy of p4c in /p4c/build by running:

docker build -t p4c .

On some platforms Docker limits the memory usage of any container, even containers used during the docker build process. On macOS in particular the default is 2GB, which is not enough to build p4c. Increase the memory limit to at least 4GB via Docker preferences or you are likely to see "internal compiler errors" from gcc which are caused by low memory.

Known issues

The P4C compiler is in early development. Issues with the compiler are tracked on GitHub. Before opening a new issue, please check whether a similar issue is already opened. Opening issues and submitting a pull request with fixes for those issues is much appreciated.

In addition to the list of issues on Github, there are a number of currently unsupported features listed below:

Frontend

P4_14 features not supported in P4_16

• extern/blackbox attributes -- there is support for carrying them in the IR, but they are lost if P4_16 code is output. Backends can access them from the IR

• Nonstandard extension primitives from P4_14

  • Execute_meter extra arguments
  • Recirculate variants
  • Bypass_egress
  • Sample_ primitives
  • invalidate

• No support for P4_14 parser exceptions.

Backends

Bmv2 Backend

• All checksum verification happens in the parser.
• Range "set" not supported in parser transitions
• Tables with multiple apply calls

See also unsupported P4_16 language features.