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Locating presence conditions in variable software systems
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README.md

PCLocator

PCLocator architecture

PCLocator is a Java tool that analyzes presence conditions in variable software systems written in the programming language C. (There are some slides available online.)

A presence condition describes under which circumstances a file or block of code is included in the compiled product. A naive, but slow solution is enumerating all possible configurations of the software.

There are better tools available to analyze variability in C. PCLocator integrates the following tools:

  • TypeChef and xtc, variability-aware C parsers
  • FeatureCoPP, a tool for physical separation of annotated features that includes a cpp parser
  • Kmax, a variability-aware analyzer Kconfig/Kbuild Makefiles

This tool addresses a challenge case of the SPLC 2018 Challenge Track and is mentioned in our paper PCLocator: A Tool Suite to Automatically Identify Configurations for Code Locations.

Getting started

The easiest way to set up PCLocator is to download a prepared JAR distribution here.

To build from source, additionally to cloning the repository, you need to download the libraries here (every JAR file but PCLocator.jar) and copy them to the lib folder. Generate the output jar from IntelliJ using Build > Build Artifacts... and run scripts/post_build.sh.

Usage

PCLocator requires Java 1.8. Run it with:

java -jar PCLocator.jar <arguments>

If you don't provide any arguments, detailed usage information will be printed.

To use one of the shell scripts described below, run chmod +x *.sh to make them executable.

Virtual Machine

PCLocator comes with a virtual machine for reproducible results. (It does not have to be used though.) To use it, install Vagrant. The JAR distribution ships with a Vagrantfile, so just run vagrant up while in the distribution folder. You will be prompted to install the hashicorp/precise64 box, a Ubuntu VM. As provider, we used VirtualBox.

When the VM is running, use vagrant ssh to enter a shell. To set up PCLocator and its dependencies (notably Java), run:

cd PCLocator
./setup.sh

After accepting the Java License Agreement, PCLocator can be used as described in this README. (Maybe consider adjusting the RAM size vb.memory in the Vagrantfile, then run vagrant reload.)

Examples

Presence condition

Extract a single presence condition for the line <line> in a C file <file> (using the default parser, a combination of the tools above):

java -jar PCLocator.jar <file>:<line>

Leave off the <line> to get a tabular overview of all presence conditions using all parsers.

To account for platform-specific macro usage, it is suggested to generate a platform header file with echo - | gcc -dM - -E -std=gnu99 and pass it with --platform.

Configuration space

Derive the satisfying configuration space from a feature model in the DIMACS format (see here and here):

java -jar PCLocator.jar --configure <dimacs_file> <file>:<line>

Only features declared in the DIMACS file are considered when deriving configurations to prevent compiler-specific macros being added to the configuration. Some DIMACS files are included in the scripts directory.

Build system

To consider build system information in projects which use Kconfig/Kbuild, you can use Kmax. PCLocator takes a Kmax unit_pc file (including presence conditions for every directory and file in the project). Have a look at kmax-vm if you want to generate such a file. Some files for Busybox and Linux are included in the scripts directory.

Run the analysis with

java -jar PCLocator.jar --locator kmax --kmaxfile <unit_pc_file> --projectroot <root_directory> <file>:<line>

<root_directory> should be the directory the entries in the unit_pc file refer to, i.e. the root directory of the analyzed project.

Explanation

When analyzing individual lines, add --explain to the command line to get an explanation for how the presence condition for the analyzed line has been located.

Analyses

Variability Bugs Database

To analyze the VBDB (Abal et. al ASE14), build PCLocator and cd into scripts/vbdb.

Use vbdb_annotate.sh to produce a file containing presence conditions and configurations for each file and quickly assess the results.

Use vbdb.sh to locate presence conditions and vbdb_configure.sh to derive configurations. Just pass them the location and any additional arguments, e.g.:

./vbdb.sh --explain splc18challengecase/vbdb/linux/simple/8c82962.c:58

vbdb_configure.sh takes as first argument the feature model:

./vbdb_configure.sh linux.dimacs splc18challengecase/vbdb/linux/simple/8c82962.c:58

Use vbdb_challenge.sh to tackle the challenge. It takes as first argument the program location to analyze (see locations.txt for reference), any following arguments are propagated to PCLocator, e.g.

./vbdb_challenge.sh splc18challengecase/vbdb/marlin/simple/2d22902.c:11 --limit 1

It will enumerate configurations that include the given program locations and generate some files in the challenge directory: the preprocessed C file, the compilation result (if any) and a log file containing any errors (a log file for each configuration and an additional log file containing all errors PCLocator returned).

Note that by default, like with the *_configure.sh scripts, the entire configuration space is enumerated. To sample, say, just one configuration, pass --limit 1 like above. (Or --timelimit 1s to limit configuration space deduction to one second. Note that the preprocessing/compilation steps may take much longer.)

For convenience, vbdb_challenge_peek.sh enumerates every location given in the challenge and analyzes only one configuration using vbdb_challenge.sh. It takes no arguments.

Evaluation has been done using vbdb_evaluate.sh. This generates CSV files and preprocessed C files with statistical information.

BusyBox

To analyze BusyBox, build PCLocator and cd into scripts/busybox. Use busybox.sh to locate presence conditions and busybox_configure.sh to derive configurations. Just pass them the location and any additional arguments, e.g.:

./busybox.sh --parser typechef busybox-1.18.5/modutils/modprobe.c:1

With busybox_compile.sh you can compile some configuration that includes the given program location. It takes as first argument the program location to analyze, any following arguments are propagated to PCLocator, e.g.

./busybox_compile.sh busybox-1.18.5/modutils/lsmod.c:50 --parser featurecopp

The final binary can be executed with busybox-1.18.5/busybox. We have only tried random samples, so compilation might fail due to libraries missing. This can be resolved by installing the missing libraries.

Evaluation has been done using busybox_evaluate.sh and busybox_sample.sh. Like with VBDB, this generates statistical information. Some evaluation results can be found in the evaluation directory.

The Kmax files have been generated using kmax-vm. The DIMACS file from the TypeChef BusyBox analysis is used.

Note that we analyze BusyBox 1.18.5 here because a feature model was freely available. For newer versions, check out KBuildMiner to transform KConfig files to a feature model.

Manual library setup

Setting up the lib folder can be a little involved, because the integrated tools depend on different versions of the same library.

Here are instructions to reproduce the libraries provided above, if needed:

  • Build TypeChef according to its instructions (sbt assembly).
  • Edit the JAR (e.g., by extracting and re-zipping it) and remove the xtc folder. This is necessary because the xtc version included by TypeChef is outdated.
  • Copy the resulting JAR to lib/TypeChef.jar.
  • Download xtc (which includes SuperC) and copy the included JAR files (ccl.jar, javabdd.jar, javacc.jar, javancss.jar, JFlex.jar, jhbasic.jar, junit.jar, rats-runtime.jar, rats.jar, xtc.jar) to lib.
  • From FeatureCoPP.jar, extract choco-solver-4.0.4-with-dependencies.jar and JCParser.jar and copy them to lib.
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