ccache is a C compiler cache.
ccache can save a large amount of compilation time on recurring builds and builds restarted from a clean repository after make clean or git clean. It is well suited for e.g. u-boot and Linux compilation.
Caching the host compiler
Caching "native" builds is easily done by adding in the beginning of your $PATH a special directory, which contains links to ccache to override the usual compiler.
On e.g. Debian this directory is readily available as /usr/lib/ccache, So you can do:
$ export PATH="/usr/lib/ccache:$PATH"
Typical links found in this folder are:
c++ -> ../../bin/ccache
cc -> ../../bin/ccache
g++ -> ../../bin/ccache
gcc -> ../../bin/ccache
etc...
Caching the cross compiler
Caching cross-compiled builds can be done in the same way as native builds, provided you create links of the form e.g. arm-linux-gnueabihf-gcc pointing to ccache.
But there is an even more convenient way for those projects, which rely on a $CROSS_COMPILE environment variable (as is the case for e.g. u-boot and Linux). You can prefix the cross compiler with ccache there in e.g. the following way:
$ export CROSS_COMPILE="ccache arm-linux-gnueabihf-"
Monitoring efficiency
Now that your builds are cached, you might want to see how much is "spared" with this technique. ccache -s will tell you all sorts of statistics, such as:
cache directory /home/vstehle/.ccache
cache hit (direct) 10852
cache hit (preprocessed) 3225
cache miss 19000
called for link 33267
called for preprocessing 9463
compile failed 3
preprocessor error 1
couldn't find the compiler 117
unsupported source language 921
unsupported compiler option 2167
no input file 31681
files in cache 51694
cache size 1.3 Gbytes
max cache size 4.0 Gbytes
Here you see a somewhat typical 50%/50% hit/miss ratio.
Enjoy!
