P4C

• Sample Backends in P4C
• Getting started
  • Installing packaged versions of P4C
  • Installing P4C from source
• Dependencies
  • Ubuntu dependencies
  • Fedora dependencies
  • macOS dependencies
  • Garbage collector
  • Crash dumps
• Development tools
  • Git setup
• Docker
• Bazel
• Build system
  • Defining new CMake targets
• Known issues
  • Frontend
  • Backends
• How to Contribute
• P4 Compiler Onboarding
• Contact

P4C is a 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. One fact attesting to the level of quality and completeness of P4C's code is that its front-end code, mid-end code, and P4C-graphs back end are used as the basis for at least one commercially supported P4 compiler.

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.

Sample Backends in P4C

P4C includes seven sample backends, catering to different target architectures and use cases:

• p4c-bm2-ss: can be used to target the P4 simple_switch written using the BMv2 behavioral model,
• p4c-dpdk: can be used to target the DPDK software switch (SWX) pipeline,
• p4c-ebpf: can be used to generate C code which can be compiled to eBPF and then loaded in the Linux kernel. The eBPF backend currently implements three architecture models: ebpf_model.p4 for packet filtering, xdp_model.p4 for XDP and the fully-featured PSA (Portable Switch Architecture) model.
• p4test: a source-to-source P4 translator which can be used for testing, learning compiler internals and debugging,
• p4c-graphs: can be used to generate visual representations of a P4 program; for now it only supports generating graphs of top-level control flows, and
• p4c-ubpf: can be used to generate eBPF code that runs in user-space.
• p4tools: a platform for P4 test utilities, including a test-case generator for P4 programs. Sample command lines:

Compile P4_16 or P4_14 source code. If your program successfully compiles, the command will create files with the same base name as the P4 program you supplied, and the following suffixes instead of the .p4:

• a file with suffix .p4i, which is the output from running the preprocessor on your P4 program.
• a file with suffix .json that is the JSON file format expected by BMv2 behavioral model simple_switch.

p4c --target bmv2 --arch v1model my-p4-16-prog.p4
p4c --target bmv2 --arch v1model --std p4-14 my-p4-14-prog.p4

By adding the option --p4runtime-files <filename>.txt as shown in the example commands below, P4C will also create a file <filename>.txt. This is a text format "P4Info" file, containing a description of the tables and other objects in your P4 program that have an auto-generated control plane API.

p4c --target bmv2 --arch v1model --p4runtime-files my-p4-16-prog.p4info.txt my-p4-16-prog.p4
p4c --target bmv2 --arch v1model --p4runtime-files my-p4-14-prog.p4info.txt --std p4-14 my-p4-14-prog.p4

All of these commands take the --help argument to show documentation of supported command line options. p4c --target-help shows the supported "target, arch" pairs.

p4c --help
p4c --target-help

Auto-translate P4_14 source to P4_16 source:

p4test --std p4-14 my-p4-14-prog.p4 --pp auto-translated-p4-16-prog.p4

Check syntax of P4_16 or P4_14 source code, without limitations that might be imposed by any particular compiler back end. There is no output for these commands other than error and/or warning messages.

p4test my-p4-16-prog.p4
p4test --std p4-14 my-p4-14-prog.p4

Generate GraphViz ".dot" files for parsers and controls of a P4_16 or P4_14 source program.

p4c-graphs my-p4-16-prog.p4
p4c-graphs --std p4-14 my-p4-14-prog.p4

Generate PDF of parser instance named "ParserImpl" generated by the p4c-graphs command above (search for graphviz below for its install instructions):

dot -Tpdf ParserImpl.dot > ParserImpl.pdf

Getting started

Installing packaged versions of P4C

P4C has package support for several Ubuntu and Debian distributions.

Ubuntu

A P4C package is available in the following repositories for Ubuntu 20.04 and newer.

source /etc/lsb-release
echo "deb http://download.opensuse.org/repositories/home:/p4lang/xUbuntu_${DISTRIB_RELEASE}/ /" | sudo tee /etc/apt/sources.list.d/home:p4lang.list
curl -fsSL https://download.opensuse.org/repositories/home:p4lang/xUbuntu_${DISTRIB_RELEASE}/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_p4lang.gpg > /dev/null
sudo apt-get update
sudo apt install p4lang-p4c

Debian

For Debian 11 (Bullseye) it can be installed as follows:

echo 'deb https://download.opensuse.org/repositories/home:/p4lang/Debian_11/ /' | sudo tee /etc/apt/sources.list.d/home:p4lang.list
curl -fsSL https://download.opensuse.org/repositories/home:p4lang/Debian_11/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_p4lang.gpg > /dev/null
sudo apt update
sudo apt install p4lang-p4c

If you cannot use a repository to install P4C, you can download the .deb file for your release and install it manually. You need to download a new file each time you want to upgrade P4C.

1. Go to p4lang-p4c package page on OpenSUSE Build Service, click on "Download package" and choose your operating system version.

2. Install P4C, changing the path below to the path where you downloaded the package.

sudo dpkg -i /path/to/package.deb

Installing P4C from source

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 20.04 here and for macOS 11 here. You can also look at the CI installation script.

3. Build. Building should also take place in a subdirectory named build.

   mkdir build
   cd build
   cmake .. <optional arguments>
   make -j4
   make -j4 check
   

   The cmake command takes the following optional arguments to further customize the build (see file CMakeLists.txt for the full list):

   • -DCMAKE_BUILD_TYPE=Release|Debug -- set CMAKE_BUILD_TYPE to Release or Debug to build with optimizations or with debug symbols to run in gdb. Default is Release.
   • -DCMAKE_INSTALL_PREFIX=<path> -- set the directory where make install installs the compiler. Defaults to /usr/local.
   • -DENABLE_BMV2=ON|OFF. Enable the bmv2 backend. Default ON.
   • -DENABLE_EBPF=ON|OFF. Enable the ebpf backend. Default ON.
   • -DENABLE_P4TC=ON|OFF. Enable the TC backend. Default ON.
   • -DENABLE_UBPF=ON|OFF. Enable the ubpf backend. Default ON.
   • -DENABLE_DPDK=ON|OFF. Enable the DPDK backend. Default ON.
   • -DENABLE_P4C_GRAPHS=ON|OFF. Enable the p4c-graphs backend. Default ON.
   • -DENABLE_P4FMT=ON|OFF. Enable the p4fmt backend. Default ON.
   • -DENABLE_P4TEST=ON|OFF. Enable the p4test backend. Default ON.
   • -DENABLE_TEST_TOOLS=ON|OFF. Enable the p4tools backend. Default OFF.
   • -DENABLE_DOCS=ON|OFF. Build documentation. Default is OFF.
   • -DENABLE_GC=ON|OFF. Enable the use of the garbage collection library. Default is ON.
   • -DENABLE_GTESTS=ON|OFF. Enable building and running GTest unit tests. Default is ON.
   • -DP4C_USE_PREINSTALLED_ABSEIL=ON|OFF. Try to find a system version of Abseil instead of a fetched one. Default is OFF.
   • -DP4C_USE_PREINSTALLED_PROTOBUF=ON|OFF. Try to find a system version of Protobuf instead of a CMake version. Default is OFF.
   • -DENABLE_ABSEIL_STATIC=ON|OFF. Enable the use of static abseil libraries. Default is ON. Only has an effect when P4C_USE_PREINSTALLED_ABSEIL is enabled.
   • -DENABLE_PROTOBUF_STATIC=ON|OFF. Enable the use of static protobuf libraries. Default is ON. Only has an effect when P4C_USE_PREINSTALLED_PROTOBUF is enabled.
   • -DENABLE_MULTITHREAD=ON|OFF. Use multithreading. Default is OFF.
   • -DBUILD_LINK_WITH_GOLD=ON|OFF. Use Gold linker for build if available.
   • -DBUILD_LINK_WITH_LLD=ON|OFF. Use LLD linker for build if available (overrides BUILD_LINK_WITH_GOLD).
   • -DENABLE_LTO=ON|OFF. Use Link Time Optimization (LTO). Default is OFF.
   • -DENABLE_WERROR=ON|OFF. Treat warnings as errors. Default is OFF.
   • -DCMAKE_UNITY_BUILD=ON|OFF . Enable unity builds for faster compilation. Default is OFF.

   If adding new targets to this build system, please see instructions.

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-ss-p4org program.p4 -o program.bmv2.json
   

If you plan to contribute to P4C, you'll find more useful information here.

Dependencies

Ubuntu 20.04 is the officially supported platform for P4C. There's also unofficial support for macOS 11. Other platforms are untested; you can try to use them, but YMMV.

• A C++17 compiler. GCC 9.1 or later or Clang 6.0 or later is required.

• git for version control

• CMake 3.16.3 or higher

• Boehm-Weiser garbage-collector C++ library

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

• Google Protocol Buffers v3.25.3 or higher for control plane API generation

• C++ boost library

• Python 3 for scripting and running tests

• Optional: Documentation generation requires Doxygen (1.12.0) 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
• graphs

Ubuntu dependencies

Most dependencies can be installed using apt-get install:

sudo apt-get install cmake g++ git automake libtool libgc-dev bison flex \
libfl-dev libboost-dev libboost-iostreams-dev \
libboost-graph-dev llvm pkg-config python3 python3-pip \
tcpdump

pip3 install --user -r requirements.txt

For documentation building:

Tools

• Download the Doxygen 1.12.0 binary

wget https://github.com/doxygen/doxygen/releases/download/Release_1_12_0/doxygen-1.12.0.linux.bin.tar.gz

• Extract and install Doxygen

tar xzvf doxygen-1.12.0.linux.bin.tar.gz
cd doxygen-1.12.0
sudo make install
cd .. 

• Install Graphviz

sudo apt-get install -y graphviz

Theme

git clone --depth 1 -b v2.3.3 https://github.com/jothepro/doxygen-awesome-css ./docs/doxygen/awesome_css

P4C also depends on Google Protocol Buffers (Protobuf). P4C requires version 3.0 or higher, so the packaged version provided in Ubuntu 20.04 should work. However, P4C typically installs its own version of Protobuf using CMake's FetchContent module (at the moment, 3.25.3). If you are experiencing issues with the Protobuf version shipped with your OS distribution, we recommend that to install Protobuf 3.25.3 from source. You can find instructions here. After cloning Protobuf and before you build, check-out version 3.25.3:

git checkout v3.25.3

Please note that while all Protobuf versions newer than 3.0 should work for P4C itself, you may run into trouble with Abseil, some extensions and other p4lang projects unless you install version 3.25.3.

P4C also depends on Google Abseil library. This library is also a pre-requisite for Protobuf of any version newer than 3.21. Therefore the use of Protobuf of suitable version automatically fulfils Abseil dependency. P4C typically installs its own version of Abseil using CMake's FetchContent module (Abseil LTS 20240116.1 at the moment).

CMake

P4C requires a CMake version of at least 3.16.3 or higher. On older systems, a newer version of CMake can be installed using pip3 install --user cmake==3.16.3. We have a CI test on Ubuntu 18.04 that uses this option, but there is no guarantee that this will lead to a successful build.

Fedora dependencies

sudo dnf install -y cmake g++ git automake libtool gc-devel bison flex \
libfl-devel gmp-devel boost-devel boost-iostreams boost-graph llvm pkg-config \
python3 python3-pip tcpdump

sudo pip3 install -r requirements.txt

For documentation building:

Tools

• Download the Doxygen 1.12.0 binary

wget https://github.com/doxygen/doxygen/releases/download/Release_1_12_0/doxygen-1.12.0.linux.bin.tar.gz

• Extract and install Doxygen

tar xzvf doxygen-1.12.0.linux.bin.tar.gz
cd doxygen-1.12.0
sudo make install
cd ..

• Install Graphviz

sudo dnf install -y graphviz

Theme

git clone --depth 1 -b v2.3.3 https://github.com/jothepro/doxygen-awesome-css ./docs/doxygen/awesome_css

You can also look at the dependencies installation script for a fresh Fedora instance.

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
  

  or with MacPorts

  sudo port install autoconf automake coreutils libtool boehmgc boost bison pkg-config
  

  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:

  • Download and install the Doxygen 1.12.0 DMG file from here.
  • Install Graphviz

  brew install graphviz
  

  Optional Documentation theme:

  git clone --depth 1 -b v2.3.3 https://github.com/jothepro/doxygen-awesome-css ./docs/doxygen/awesome_css
  

  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 use the version of Protobuf which is supplied with CMake's fetchcontent (3.25.3).

  The protobuf formula requires the following CMake variables to be set, otherwise CMake does not find the libraries or fails in linking. It is likely that manually installed Protobuf will require similar treatment.

  PB_PREFIX="$(brew --prefix --installed protobuf)"
  ./bootstrap.sh \
    -DProtobuf_INCLUDE_DIR="${PB_PREFIX}/include/" \
    -DProtobuf_LIBRARY="${PB_PREFIX}/lib/libprotobuf.dylib" \
    -DENABLE_PROTOBUF_STATIC=OFF
  

Garbage collector

P4c relies on BDW garbage collector to manage its memory. By default, the P4C executables are linked with the garbage collector library. When the GC causes problems, this can be disabled by setting ENABLE_GC cmake option to OFF. However, this will dramatically increase the memory usage by the compiler, and may become impractical for compiling large programs. Do not disable the GC, unless you really have to. We have noticed that this may be a problem on MacOS.

Crash dumps

P4c will use libbacktrace to produce readable crash dumps if it is available. This is an optional dependency; if it is not available everything should build just fine, but crash dumps will not be very readable.

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 or newer 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 build code documentation, after installing Doxygen and the other required packages:

# Starting from root directory of your copy of p4c repo
cd docs/doxygen
doxygen doxygen.cfg

The HTML output is available in docs/doxygen/build/html/index.html.

Git setup

Occasionally formatting commits are applied to P4C. These pollute the git history. To ignore these commits in git blame, run this command git config blame.ignoreRevsFile .git-blame-ignore-revs

The P4C code base is subject to a series of linter checks which are checked by CI. To avoid failing these checks and wasting unnecessary CI cycles and resources, you can install git commit hooks by running ./tools/install_git_hooks.sh These commit hooks will run on every commit and check the files you are planning to commit with cpplint and clang-format.

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.

Bazel

The project can also be build using Bazel:

bazel build //...

We run continuous integration to ensure this works with the latest version of Bazel.

We also provide a p4_library rule for invoking P4C during the build process of 3rd party Bazel projects.

See bazel/example for an example of how to use or extend P4C in your own Bazel project. You may use it as a template to get you started.

Build system

The build system is based on cmake. This section describes how it can be customized.

Defining new CMake targets

When building a new backend target, add it into the development tree in the extensions subdirectory. The cmake-based build system will automatically include it if it contains a CMakeLists.txt file.

For a new backend, the cmake file should contain the following rules:

IR definition files

Backend specific IR definition files should be added to the global list of IR_DEF_FILES as they are processed together with the core IR files. Use the following rule:

set (IR_DEF_FILES ${IR_DEF_FILES} ${MY_IR_DEF_FILES} PARENT_SCOPE)

where MY_IR_DEF_FILES is a list of file names with absolute path (for example, use ${CMAKE_CURRENT_SOURCE_DIR}).

If in addition you have additional supporting source files, they should be added to the ir sources, as follows:

set(EXTENSION_IR_SOURCES ${EXTENSION_IR_SOURCES} ${MY_IR_SRCS} PARENT_SCOPE)

Again, MY_IR_SRCS is a list of file names with absolute path.

Source files

Sources (.cpp and .h) should be added to the cpplint and clang-format target using the following rule:

add_cpplint_files (${CMAKE_CURRENT_SOURCE_DIR} "${MY_SOURCES_AND_HEADERS}")
add_clang_format_files (${CMAKE_CURRENT_SOURCE_DIR} "${MY_SOURCES_AND_HEADERS}")

Python files should be added to the black and isort target using the following rule:

add_black_files (${CMAKE_CURRENT_SOURCE_DIR} "${MY_SOURCES_AND_HEADERS}")

The P4C CMakeLists.txt will use that name to figure the full path of the files to lint.

clang-format, black, and isort need to be installed before the linter can be used. They can be installed with the following command:

pip3 install --user "clang-format==18.1.0" "black==24.3.0" "isort==5.13.2"

clang-format can be checked using the make clang-format command. Complaints can be fixed by running make clang-format-fix-errors. black and isort can be checked using the make black or make isort command respectively. Complaints can be fixed by running make black-fix-errors or make isort-fix-errors.

cpplint, clang-format, and black/isort run as checks as port of P4C's continuous integration process. To make sure that these tests pass, we recommend installing the appropriate git hooks. This can be done by running

./tools/install_git_hooks.sh

clang-format, cpplint, and black/isort checks will be enforced on every branch commit. In cases where checks are failing but the commit is sound, one can bypass the hook enforcement using git commit --no-verify.

Target

Define a target for your executable. The target should link against the core P4C_LIBRARIES and P4C_LIB_DEPS. P4C_LIB_DEPS are package dependencies. If you need additional libraries for your project, add them to P4C_LIB_DEPS.

In addition, your target should depend on the genIR target, since you need all the IR generation to happen before you start compiling your backend. If you chose to have your backend as a library (seem the backends/bmv2 example), the library should depend on genIR, and there is no longer necessary for your executable to depend on it.

add_executable(p4c-mybackend ${MY_SOURCES})
target_link_libraries (p4c-mybackend ${P4C_LIBRARIES} ${P4C_LIB_DEPS})
add_dependencies(p4c-mybackend genIR)

Tests

We implemented support equivalent to the automake make check rules. All tests should be included in make check and in addition, we support make check-* rules. To enable this support, add the following rules:

set(MY_DRIVER <driver or compiler executable>)

set (MY_TEST_SUITES
  ${P4C_SOURCE_DIR}/testdata/p4_16_samples/*.p4
  ${P4C_SOURCE_DIR}/testdata/p4_16_errors/*.p4
  )
set (MY_XFAIL_TESTS
  testdata/p4_16_errors/this_test_fails.p4
 )
p4c_add_tests("mybackend" ${MY_DRIVER} "${MY_TEST_SUITES}" "${MY_XFAIL_TESTS}")

In addition, you can add individual tests to a suite using the following macro:

set(isXFail FALSE)
set(SWITCH_P4 testdata/p4_14_samples/switch_20160512/switch.p4)

p4c_add_test_with_args ("mybackend" ${MY_DRIVER} ${isXFail}
  "switch_with_custom_profile" ${SWITCH_P4} "-DCUSTOM_PROFILE")

See the documentation for p4c_add_test_with_args and p4c_add_tests for more information on the arguments to these macros.

To pass custom arguments to P4C, you can set the environment variable P4C_ARGS:

make check P4C_ARGS="-Xp4c=MY_CUSTOM_FLAG"

When making changes to P4C, it is sometimes useful to be able to run the tests while overwriting the expected output files that are saved in this repository. One such situation is when your changes to P4C cause the names of compiler-generated local variables to change. To force the expected output files to be rewritten while running the tests, assign a value to the shell environment variable P4TEST_REPLACE. Here is one example Bash command to do so:

P4TEST_REPLACE=1 make check

Installation

Define rules to install your backend. Typically you need to install the binary, the additional architecture headers, and the configuration file for the P4C driver.

install (TARGETS p4c-mybackend
  RUNTIME DESTINATION ${P4C_RUNTIME_OUTPUT_DIRECTORY})
install (DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/p4include
  DESTINATION ${P4C_ARTIFACTS_OUTPUT_DIRECTORY})
install (FILES ${CMAKE_CURRENT_SOURCE_DIR}/driver/p4c.mybackend.cfg
  DESTINATION ${P4C_ARTIFACTS_OUTPUT_DIRECTORY}/p4c_src)

Known issues

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/clone/resubmit variants
  • Bypass_egress
  • Sample_ primitives
  • invalidate

• No support for P4_14 parser exceptions.

Backends

Bmv2 Backend

• Tables with multiple apply calls

See also unsupported P4_16 language features.

How to Contribute

We welcome and appreciate new contributions. Please take a moment to review our Contribution Guidelines to get started.

P4 Compiler Onboarding

Educational material on P4:

• General hands-on tutorials.
• Technical documentation on P4-related topics.
• Motivating P4: IEEE ICC 2018 // Keynote: Nick McKeown, Programmable Forwarding Planes Are Here To Stay
• Introducing P4-16 in detail:
  • Part 1: Introduction to P4_16. Part 1
  • Part 2: Introduction to P4_16. Part 2
• Material on the official P4 compiler:
  • Understanding the Open-Source P4-16 Compiler - February 15, 2022 - Mihai Budiu
  • Understanding P4-16 Open-Source Compiler, Part 2 - March 1, 2022 - Mihai Budiu
  • Compiler Design - Implementation Architecture.
• Introduction to P4Runtime: Next-Gen SDN Tutorial - Session 1: P4 and P4Runtime Basics

Contact

We appreciate your contributions and look forward to working with you to improve the P4 Compiler Project (P4C)!

• For further assistance or questions regarding contributions, reach out to us in our community chat. Joining link .
• For general P4-related questions, use the P4 forum.
• For other communication channels click here.