Clang patching

Dovecot is developed with some extra warning features developed for clang. Here’s how to build such a patched clang.

Prerequisites

To build llvm/clang, you’ll need cmake version 3.4.3.

Source Repos

There are github mirrors, but you can clone directly from llvm.org.

git clone https://llvm.org/git/llvm
cd tools
git clone https://llvm.org/git/clang

Here are some hints on how to build/hack clang:

  • If you want to debug clang with gdb, you need to have a debug build. This used to be the default, but apparently not nowadays. Note that Debug build takes ~15 GB of space vs non-debug build 5 GB. cmake -DCMAKE_BUILD_TYPE=Debug

  • With debug build you still want it to be optimized or the resulting compiler will be horribly slow. cmake -DLLVM_OPTIMIZED_TABLEGEN=ON

  • Even then it seems to be very slow. It’s possibly enough to use -DCMAKE_BUILD_TYPE=RelWithDebInfo

mkdir build
cd build
cmake -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++
-DLLVM_OPTIMIZED_TABLEGEN=ON -DCMAKE_BUILD_TYPE=Debug -G "Unix
Makefiles" ../

If you want to debug clang, you need to debug “clang -cc1” because otherwise it forks a new process and you can’t do much with it. See https://clang.llvm.org/docs/FAQ.html#id2

Dovecot Patches

Dovecot has some clang patches in https://dovecot.org/patches/clang/

These patches aid with sanity checking the dovecot build, e.g. static code analysis:

  • clang-strict-bool.diff - This is the most important one that implements -Wstrict-bool

  • clang-default-nonnull.diff - Add support for automatically marking pointer parameters as non-null. This was never fully implemented to work nicely.