Development/Clang Code Analysis

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Clang Code Analysis

This short tutorial aims to describe how to run the Clang static code analyzer to generate reports.

Example results

Example generated results can be found here:

https://dev-builds.libreoffice.org/clang_reports/

Generated by this script: https://git.libreoffice.org/dev-tools/+/master/scan-build-report/scan-build-report.sh

Pre-requisites

Set up build environment

Follow the guidelines at: Building on Linux to set up your LibreOffice build environment.

Install LLVM/Clang packages

To install the binary packages that come with your Linux distribution run following commands.

On Ubuntu/Debian, you can install with command:

sudo apt install llvm clang clang-tools

On Fedora, you can install the packages by running this command:

sudo yum install llvm clang clang-analyzer

Install LLVM/Clang from source

Installing LLVM and Clang from the latest sources is recommended, as at the time of writing this tutorial c++ analysis is still very much a work in progress, and it makes sense to use the latest code with the best support for c++ analysis. You can install from scratch by following this guide:

https://clang.llvm.org/get_started.html

When running ./configure llvm/clang, please specify --enable-optimized. The default build generates a (bigger, slower) debug build. This switch generates a release build of llvm/clang.

../llvm/configure --enable-optimized

Install C++ Analyzer

In current versions of the build system, the analyzer does get installed when running make install.

Configure and build LibreOffice

Run ./autogen.sh

First you need to configure your build environment for analysis. This is done by running the scan-build command. A short tutorial about it can be found here: https://clang-analyzer.llvm.org/scan-build.html

scan-build --use-cc=clang --use-c++=clang++ ./autogen.sh

Note:

If you have clang installed in a non standard path, you need --use-analyzer=[directory of your clang binary file] even if Clang is already in $PATH.

Run ./configure.sh

Now we can build and analyze the LibreOffice code. By default the analyzer works by inserting the clang analyzer and performing the analysis before the code gets build. It does this by using Clang for analysis, and the default compiler (GCC in this case) alone. This is the least intrusive way of functioning for Clang. However, although Clang is meant as a drop-in replacement for GCC, it is not 100% compatible in some corner-cases. Unfortunately, some of these are hit in LibreOffice. Therefore we need to override the default behavior and also compile with Clang using --use-cc=clang --use-c++=clang++. I ran into weird issues when using ccache, where the analyzer tried to analyze all the files located in the cache. So I disabled it using --disable-ccache.

I enabled a debug build of LibreOffice, as there are some instances where debug code can assist the analyzer.

As much of the system libraries instead of the internal libreoffice supplied ones are used by specifying '--with-system-libs'.

scan-build --use-cc=clang --use-c++=clang++ ./configure --disable-ccache --enable-debug \ 
--with-system-libcmis=no --with-system-hsqldb=no --with-system-saxon=no --with-system-libs

Run make

You can now analyze+build LibreOffice.

mkdir /tmp/libreoffice
scan-build --use-cc=clang --use-c++=clang++ -o /tmp/libreoffice make

Done

You should now have the generated HTML report files.