is ccache working?

[Alexander Neundorf]

On Tuesday 03 August 2010, matthew wrote:
> On Sunday 01 August 2010 07:16:05 fabio de francesco wrote:
> > On Sunday 01 August 2010 11:42:29 Andreas Pakulat wrote:
> > > On 01.08.10 11:19:19, fabio de francesco wrote:
> > > > Hi all,
> > > >
> > > > I have the line "export CCACHE_DIR=/home/kdevel/var/tmp/ccache" in my
> > > > /home/kdevel/.bashrc but I don't find any file in that directory. Did
> > > > I miss something needed to make ccache properly working?
> > >
> > > This doesn't really have anything to do with KDE, you need to make sure
> > > that gcc/g++/... are pointing to ccache and not the real compiler.
> > > Usually this is done by setting up apropriate symlinks called gcc/g++
> > > somewhere in a directory and putting that directory first in PATH.
> > >
> > > Andreas
> >
> > I see that /usr/bin/gcc is not a symbolic link to ccache, anyway ccache
> > is working system wide and it regularly writes caches to /var/tmp/ccache.
> > By using "find /var/tmp/ccache -cmin 60" I see that these files are
> > regularly updated when I compile programs with Gentoo's "emerge world".
> > Because of ccache working with system updates I wouldn't make links that
> > can break things as they are now.
> >
> > Therefore I've made both /home/kdevel/bin/g++ and /home/kdevel/bin/gcc
> > symbolic links to /usr/bin/ccache. The /home/kdevel/bin directory is the
> > first listed in $PATH for the kdevel user. After doing this I re-compiled
> > kdelibs as kdevel user and then I checked /home/kdevel/var/tmp/ccache,
> > but the directory is still empty.
> >
> > I think this problem is KDE related because the advice to export
> > CCACHE_DIR in ~/.bashrc is taken from the tutorial in developing KDE from
> > the
> > techbase.kde.org site.
> >
> > Please, what am I missing?
> >
> > Regards,
> >
> > fabio
>
> One thing to take note of, cmake, when first runs, stores the complete path
> to gcc in the CMakeCache.txt.  It will not update this value normally. 
> Even if the path changes, it remains constant.  So adding ccache to your
> path will *not* make KDE's build use ccache.  You either have to manually
> replace the value (as far as I know, unsupported and dangerous), or
> recreate your build directory.  I seem to remember reading about this
> behaviour inside of cmake's documentation, so I don't think this is KDE
> specific.

Yes, that's correct.
CMake stores the full path to the compiler in the cache, and you should not 
manually change that.
All other values in the cache, like the results of try_compile() etc., have 
been produced with that compiler, if you change the compiler, they all might 
be wrong. So, don't (manually) change the compiler in an existing build tree.

Alex