By
Sylvestre Ledru (
Debian,
IRILL).
Presentation
This document presents the result of the rebuild of the Debian archive (the distribution) with clang, a C/C++ compiler.
clang is now ready to build software for production (either for C, C++ or Objective-C). This compiler is providing many more warnings and interesting errors than the gcc suite while not carrying the same legacy as gcc.
This rebuild has several goals. The first one is to prove (or not) that clang is a viable alternative. Second, building a software with different compilers improves the overall quality of code by providing different checks and alerts.
Rebuild results
The detailed list of errors with clang 13.0.0:
A
maintainer view is also available. This shows per developers which packages should be fixed.
Errors can be caused by several reasons:
Of course, a bug can hide other bugs.
Bugs (with patches) will be reported in the Debian bug tracker.
They will be tagged as wishlist.
Detailed results
The full list of all the results with logs are available at the following URL:
Status
The Debian archive is regularly rebuilt against the latest version of clang. This to achieve three goals:
1) See which packages get fixed
2) See the impact of new clang releases
3) Find bugs or gcc-compatibility issues in gcc itself
Annexes
Rebuild
The 2.9 and 3.0 rebuild itself have been done on a cluster called Grid 5000.
3.1, 3.2 and later rebuilds have been done on AWS, the Amazon cloud, sponsoring Debian.
Each packages in the Debian archive has been rebuild with the chroot described further.
For each packages failing to build from the source with clang, the package has been rebuild with a "normal" Debian sid chroot. If working, we considered that it was due to a clang bug. Otherwise, the package is not listed in this list.
Configuration of the chroot
The procedure for 2.9 & 3.0 was the following:
- a chroot has been created with a minimal build environment
- gcc and g++ have been put on hold to make sure then are not changed during the installation of the dependencies
(echo "gcc hold"|dpkg --set-selections)
- clang 3.0-5 has been installed (no changes from the version available in the
Debian archive has been made)
- /usr/bin/gcc, /usr/bin/g++ and /usr/bin/cpp symlinks has been changed to point to clang
- g++-4.6, gcc-4.6 and cpp-4.6 have been removed to make sure they are not used.
VERSION=4.6
cd /usr/bin
rm g++-$VERSION gcc-$VERSION cpp-$VERSION
ln -s clang++ g++-$VERSION
ln -s clang gcc-$VERSION
ln -s clang cpp-$VERSION
cd -
All packages of the archive (15658 sources packages) have been rebuild this chroot (even the one without any C or C++ code). Build dependencies used are the same as Debian. For example, that means that the libxml2 used to build a package will be the one from Debian, not the one built with clang.
From clang 3.1, with the EC2 Amazon cloud, an
chroot-setup-commands is used for each sbuild to setup the environnement.
The init code is the following:
apt-get update
echo "Install of clang"
apt-get update
apt-get install --yes --no-install-recommends clang -t unstable
echo "Replace gcc, g++ & cpp by clang"
cd /usr/bin
VERSIONS="4.8 4.7 4.6"
for VERSION in $VERSIONS; do
rm g++-$VERSION gcc-$VERSION cpp-$VERSION
ln -s clang++ g++-$VERSION
ln -s clang gcc-$VERSION
ln -s clang cpp-$VERSION
done
echo "Block the installation of new gcc version"
echo "gcc-4.6 hold"|dpkg --set-selections
echo "cpp-4.6 hold"|dpkg --set-selections
echo "g++-4.6 hold"|dpkg --set-selections
echo "gcc-4.7 hold"|dpkg --set-selections
echo "cpp-4.7 hold"|dpkg --set-selections
echo "g++-4.7 hold"|dpkg --set-selections
echo "Check if gcc, g++ & cpp are actually clang"
gcc --version|grep clang > /dev/null || exit 1
The same procedure has been used for the 3.2 rebuild except that the clang packages have been rebuild for unstable (instead of the experimental packages).
Acknowledgments
Many thanks to
Lucas Nussbaum for his time and patience.
Stefano Zacchiroli for the review (among other things).
Thanks also to
Grid 5000 for their infrastructure and Amazon for their credit to use AWS.
