Development Tips

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.

Code Coverage Testing

Compile using --coverage flags:

$ EXTRA_CFLAGS=--coverage EXTRA_LDFLAGS=--coverage ./configure

Build and run unit tests:

$ make check NOVALGRIND=1

Get coverage as HTML:

$ lcov -q --directory . --capture -o cov.info
$ summary="`lcov --summary cov.info 2>&1 \| sed -e 's/$/<br>/'`"
$ genhtml -q -k --legend -o cov cov.info

The HTML content is now in the "cov" directory. Note that the lcov command can generate some warnings about missing *.gcda files, like:

geninfo: WARNING: gcov did not create any files for .../src/lib-otp/.libs/otp-parity.gcda!
geninfo: WARNING: gcov did not create any files for .../src/lib/.libs/ioloop-notify-kqueue.gcda!
geninfo: WARNING: gcov did not create any files for .../src/lib/.libs/ioloop-notify-none.gcda!

clang

If using clang, create llvm-gcov.sh script:

#!/bin/bash
exec llvm-cov gcov "$@"

Then add --gcov-tool llvm-gcov.sh parameter:

$ lcov -q --gcov-tool llvm-gcov.sh --directory . --capture -o cov.info

Issues

Code coverage output isn't written if _exit() is used.