Re: gcov/lcov problems with branch coverage and c++

[andre maute <andre dot maute at gmx dot de>]

On 02/02/2017 02:59 PM, Sven Eppler wrote:
> Hello,
> we are using GCOV/LCOV to produce test coverage for our projects.
> Recently we tried to enable branch-coverage additionally.
> But it looks like, this just doesn't yield the results we expected 
> from a high level developer view.
>
> I created a small test project to show the problem:
>
>    https://github.com/ghandmann/lcov-branch-coverage-weirdness
>
> Currently we use Ubuntu 16.04. with:
>  - gcc v5.4
>  - lcov & genhtml v1.12
>
> Our production code is build with c++11 enabled. The minimal example 
> isn't build with c++11 enabled,
> but as we experimented a bit with all different options (c++ standard, 
> optimization, -fno-exceptions)
> we didn't came up with a passable result. 

Experimenting on my Fedora with lcov 1.12 (not 1.13) and a fedora repo 
gcc-6.3.1 for fc24

$ g++ -vUsing built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/6.3.1/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap 
--enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr 
--mandir=/usr/share/man --infodir=/usr/share/info 
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared 
--enable-threads=posix --enable-checking=release --enable-multilib 
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions 
--enable-gnu-unique-object --enable-linker-build-id 
--with-linker-hash-style=gnu --enable-plugin --enable-initfini-array 
--disable-libgcj --with-isl --enable-libmpx 
--enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 
--build=x86_64-redhat-linux
Thread model: posix
gcc version 6.3.1 20161221 (Red Hat 6.3.1-1) (GCC)

The two variants
a) -fno-exceptions
b) -std=c++11 -fno-exceptions
give three times 100 percent

If you don't 'shut-down' the exceptions the branch coverage will be at 
60 percent.

Regards Andre