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Crab: A C++ Library for Building Program Static Analyses

Crab is a C++ library for building program static analyses based on Abstract Interpretation. Crab provides a rich set of abstract domains, Kleene-based fixpoint solvers, as well as different analyses such as dataflow, inter-procedural and backward. The design of Crab is quite modular so that it is easy to plugin new abstract domains and solvers or build new analyses.

Crab abstract domains can reason about memory contents, C-like arrays and numerical properties. Crab uses efficient implementations of popular numerical domains such as Zones and Octagons and novel domains to reason, for instance, about symbolic terms (aka uninterpreted functions). Crab also implements popular non-relational domains such as interval or congruences using efficient environment maps, and allows the combination of arbitrary domains via standard reduced product constructions. Crab also provides non-convex domains such as specialized disjunctive intervals called Boxes based on linear decision diagrams and a more general value partitioning strategy that lifts an arbitrary domain to an over-approximation of its disjunction completion. In addition to these domains, all developed by Crab authors, the Crab library integrates popular abstract domain libraries such as Apron, Elina, and PPLite.

Crab provides the state-of-the-art interleaved fixpoint solver that uses Bourdoncle's Weak Topological Ordering to select the set of widening points. To mitigate precision losses during widening, Crab implements some popular techniques such as widening with thresholds and lookahead widening.

Crab provides two different implementations of inter-procedural analyses: a top-down with memoization inter-procedural analysis with support for recursive calls, and a hybrid of bottom-up + top down analysis. Last but not least, Crab also implements a more experimental backward analysis that can be used to compute necessary preconditions and/or reduce the number of false alarms.

Crab does not analyze directly a mainstream programming language but instead it analyzes its own CFG-based intermediate representation called CrabIR. CrabIR is three-address code and it is strongly typed. In CrabIR, control flow is defined via non-deterministic goto instructions. Apart from standard boolean and arithmetic operations, CrabIR provides special assume and assert statements. The former can be used to refine the control flow and the latter provides a simple mechanishm to check for user-defined properties. In spite of its simple design, CrabIR is rich enough to represent languages such as LLVM.

Crab is actively under development. If you find a bug please open an Github issue. Pull requests with new features are very welcome. The available documentation can be found in our wiki. If you use this library please cite this paper.

Docker

A (nightly) pre-built version of Crab that runs all tests can be obtained using Docker:

docker pull seahorn/crab:bionic
docker run -v `pwd`:/host -it seahorn/crab:bionic

Requirements

Crab is written in C++ and relies on the Boost library. The main requirements are:

• C++11 compiler
• Boost >= 1.65
• GMP
• MPFR (if -DCRAB_USE_APRON=ON or -DCRAB_USE_ELINA=ON)
• FLINT (only if -DCRAB_USE_PPLITE=ON)

In linux, you can install requirements typing the commands:

sudo apt-get install libboost-all-dev libboost-program-options-dev
sudo apt-get install libgmp-dev
sudo apt-get install libmpfr-dev	
sudo apt-get install libflint-dev

Compilation and Installation

To install Crab, type:

 1. mkdir build && cd build
 2. cmake -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR ../
 3. cmake --build . --target install 

The tests directory contains many examples of how to build programs written in CrabIR and compute invariants using different analyses and abstract domains. To compile these tests add option -DCRAB_ENABLE_TESTS=ON to line 2.

and then, for instance, to run test1:

build/test-bin/test1

Include third-party abstract domain libraries

The Boxes/Apron/Elina/PPLite domains require third-party libraries. To avoid the burden to users who are not interested in those domains, the installation of the libraries is optional.

• If you want to use the Boxes domain then add -DCRAB_USE_LDD=ON option.

• If you want to use the Apron library domains then add -DCRAB_USE_APRON=ON option.

• If you want to use the Elina library domains then add -DCRAB_USE_ELINA=ON option.

• If you want to use the PPLite library domains then add -DCRAB_USE_PPLITE=ON option.

Important: Apron and Elina are currently not compatible so you cannot enable -DCRAB_USE_APRON=ON and -DCRAB_USE_ELINA=ON at the same time.

For instance, to install Crab with Boxes and Apron, type:

 1. mkdir build && cd build
 2. cmake -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR -DCRAB_USE_LDD=ON -DCRAB_USE_APRON=ON ../
 3. cmake --build . --target ldd && cmake ..
 4. cmake --build . --target apron && cmake ..	
 5. cmake --build . --target install 	

Lines 3 and 4 will download, compile and install the Boxes and Apron domains, respectively. Replace apron at line 4 with elina or pplite if you want to use Elina or PPLite instead. If you have already compiled and installed these libraries in your machine then skip commands at line 3 and 4 and add the following options at line 2.

• For Apron: -DAPRON_ROOT=$APRON_INSTALL_DIR
• For Elina: -DELINA_ROOT=$ELINA_INSTALL_DIR
• For Boxes: -DCUDD_ROOT=$CUDD_INSTALL_DIR -DLDD_ROOT=$LDD_INSTALL_DIR
• For PPLite: -DPPLITE_ROOT=$PPLITE_INSTALL_DIR -DFLINT_ROOT=$FLINT_INSTALL_DIR

Using Crab library in other C++ projects

To include Crab in your C++ application you need to:

• Include the C++ header files located at the $INSTALL_DIR/crab/include, and

• Link your application with the Crab libraries installed in $INSTALL_DIR/crab/lib.

If you compile with Boxes/Apron/Elina/PPLite you need also to include $INSTALL_DIR/EXT/include and link with $INSTALL_DIR/EXT/lib where EXT=apron|elina|ldd|pplite.

CMake

If your project uses cmake then you just need to add in your project's CMakeLists.txt:

add_subdirectory(crab)
include_directories(${CRAB_INCLUDE_DIRS})

And then link your executable with ${CRAB_LIBS}

Make

If your project uses make, read this sample Makefile.