Debian Package rebuild
Rebuild of the Debian archive with clang
By Sylvestre Ledru (Debian, IRILL).
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.
The detailed list of errors with clang 13.0.0:
33859 packages have been rebuild. Among them, 994 (2.9 %) failed.
Most of the errors are explained with test cases.
| Type of error | Occurrence | clang % / Debian % | |
|---|---|---|---|
| Some headers could not be found | 75 | 7.55% / 0.22% | List of errors |
| Cannot be narrowed | 69 | 6.94% / 0.2% | List of errors |
| Linker error | 63 | 6.34% / 0.19% | List of errors |
| Testsuite is failing with clang | 62 | 6.24% / 0.18% | List of errors |
| Could not find objective C headers | 59 | 5.94% / 0.17% | List of errors |
| C++11 requires a space between literal and identifier - new in 3.8 | 50 | 5.03% / 0.15% | List of errors |
| Missing symbols at link time | 46 | 4.63% / 0.14% | List of errors |
| non-void function should return a value | 34 | 3.42% / 0.1% | List of errors |
| Relocation error | 27 | 2.72% / 0.08% | List of errors |
| Unknown argument in the command line | 18 | 1.81% / 0.05% | List of errors |
| Expected declaration (#define missing?) | 18 | 1.81% / 0.05% | List of errors |
| Variable set but not used - new in 13.0.0 | 18 | 1.81% / 0.05% | List of errors |
| No support of nested C function | 16 | 1.61% / 0.05% | List of errors |
| Unknown warning option | 15 | 1.51% / 0.04% | List of errors |
| Security: Format string is not a string literal | 14 | 1.41% / 0.04% | List of errors |
| Not allowed args fails the build | 12 | 1.21% / 0.04% | List of errors |
| Cannot find member in the struct | 11 | 1.11% / 0.03% | List of errors |
| Cannot use -o use multiple output | 10 | 1.01% / 0.03% | List of errors |
| Wrong main declaration | 10 | 1.01% / 0.03% | List of errors |
| Some files are gone in the process | 10 | 1.01% / 0.03% | List of errors |
| Redefinition failed | 8 | 0.8% / 0.02% | List of errors |
| No viable overloaded | 7 | 0.7% / 0.02% | List of errors |
| Unqualified lookup in templates | 6 | 0.6% / 0.02% | List of errors |
| Linker option unused | 6 | 0.6% / 0.02% | List of errors |
| Preprocessor differences | 6 | 0.6% / 0.02% | List of errors |
| Unsupported argument with another option | 5 | 0.5% / 0.01% | List of errors |
| Conflicting types | 5 | 0.5% / 0.01% | List of errors |
| Variable length array in structure won't be supported | 5 | 0.5% / 0.01% | List of errors |
| No matching function call | 5 | 0.5% / 0.01% | List of errors |
| No matching member or constructor call | 5 | 0.5% / 0.01% | List of errors |
| Void function should not return a value | 5 | 0.5% / 0.01% | List of errors |
| Missing exception specification | 5 | 0.5% / 0.01% | List of errors |
| Unknown Type Name | 4 | 0.4% / 0.01% | List of errors |
| Ambiguous declaration | 4 | 0.4% / 0.01% | List of errors |
| Argument unused caused failure | 4 | 0.4% / 0.01% | List of errors |
| Deprecated copy - new in 10.0 | 4 | 0.4% / 0.01% | List of errors |
| Unsupported include directive within macro arg | 4 | 0.4% / 0.01% | List of errors |
| Source think that it is Mac Os X because of clang | 4 | 0.4% / 0.01% | List of errors |
| Multiple definition | 3 | 0.3% / 0.01% | List of errors |
| Use of old GNU field designator | 3 | 0.3% / 0.01% | List of errors |
| Parameter list without types not allowed | 3 | 0.3% / 0.01% | List of errors |
| Ignored or unknown attributes | 3 | 0.3% / 0.01% | List of errors |
| does not allow access declarations - new in 6.0 | 3 | 0.3% / 0.01% | List of errors |
| Cannot pass non-trivial object of type 'xx' to variadic function - new in 6.0 | 3 | 0.3% / 0.01% | List of errors |
| implicit conversions | 3 | 0.3% / 0.01% | List of errors |
| Unsupported option | 2 | 0.2% / 0.01% | List of errors |
| Equality comparison with extraneous parentheses | 2 | 0.2% / 0.01% | List of errors |
| Access to a protected member | 2 | 0.2% / 0.01% | List of errors |
| Member is not a structure or union | 2 | 0.2% / 0.01% | List of errors |
| Explicit Specialization after instantiation | 2 | 0.2% / 0.01% | List of errors |
| Could not find a library | 2 | 0.2% / 0.01% | List of errors |
| Potential usage of an uninitialized variable | 2 | 0.2% / 0.01% | List of errors |
| The build timeout | 2 | 0.2% / 0.01% | List of errors |
| Forward declaration of class cannot have a nested name specifier | 2 | 0.2% / 0.01% | List of errors |
| Hides overloaded virtual function | 2 | 0.2% / 0.01% | List of errors |
| Implicit function error | 2 | 0.2% / 0.01% | List of errors |
| -Wvarargs: undefined behavior with va_start - new in 3.9 | 2 | 0.2% / 0.01% | List of errors |
| Optimization flag is not supported - new in 4.0 | 2 | 0.2% / 0.01% | List of errors |
| qmake: failed to parse default search paths from compiler - new in 6.0 | 2 | 0.2% / 0.01% | List of errors |
| Missing field initializer | 2 | 0.2% / 0.01% | List of errors |
| Moving a temporary object prevents copy elision | 2 | 0.2% / 0.01% | List of errors |
| Overrides a member function but is not marked override | 2 | 0.2% / 0.01% | List of errors |
| Unqualified lookup into dependent bases of class templates | 1 | 0.1% / 0% | List of errors |
| Configure failed | 1 | 0.1% / 0% | List of errors |
| Tautological comparison | 1 | 0.1% / 0% | List of errors |
| Unused parameter | 1 | 0.1% / 0% | List of errors |
| Unused function | 1 | 0.1% / 0% | List of errors |
| Cannot initialize a element | 1 | 0.1% / 0% | List of errors |
| Changes of default constructor | 1 | 0.1% / 0% | List of errors |
| Wrong C++ default declaration in a method | 1 | 0.1% / 0% | List of errors |
| Embedded directive has undefined behavior | 1 | 0.1% / 0% | List of errors |
| Header guard failure | 1 | 0.1% / 0% | List of errors |
| Absolute value error - new in 3.5.0 | 1 | 0.1% / 0% | List of errors |
| Invalid instruction mnemonic | 1 | 0.1% / 0% | List of errors |
| Unknown/unexpected directive | 1 | 0.1% / 0% | List of errors |
| Initializer element not compile-time constant | 1 | 0.1% / 0% | List of errors |
| Tautological pointer comparison - new in 3.5.0 | 1 | 0.1% / 0% | List of errors |
| Incorrect conversion - new in 3.6.0 | 1 | 0.1% / 0% | List of errors |
| Explicitly assigning value of variable | 1 | 0.1% / 0% | List of errors |
| illegal storage class on function | 1 | 0.1% / 0% | List of errors |
| Not categorized | 192 | 19.32% / 0.57% | List of errors |
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.
The full list of all the results with logs are available at the following URL:
The Debian archive is regularly rebuilt against the latest version of clang. This to achieve three goals:
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.
The procedure for 2.9 & 3.0 was the following:
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).
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.