| // -*- mode:doc; -*- |
| // vim: set syntax=asciidoc: |
| |
| [[ccache]] |
| ==== Using +ccache+ in Buildroot |
| |
| http://ccache.samba.org[ccache] is a compiler cache. It stores the |
| object files resulting from each compilation process, and is able to |
| skip future compilation of the same source file (with same compiler |
| and same arguments) by using the pre-existing object files. When doing |
| almost identical builds from scratch a number of times, it can nicely |
| speed up the build process. |
| |
| +ccache+ support is integrated in Buildroot. You just have to enable |
| +Enable compiler cache+ in +Build options+. This will automatically |
| build +ccache+ and use it for every host and target compilation. |
| |
| The cache is located in +$HOME/.buildroot-ccache+. It is stored |
| outside of Buildroot output directory so that it can be shared by |
| separate Buildroot builds. If you want to get rid of the cache, simply |
| remove this directory. |
| |
| You can get statistics on the cache (its size, number of hits, |
| misses, etc.) by running +make ccache-stats+. |
| |
| The make target +ccache-options+ and the +CCACHE_OPTIONS+ variable |
| provide more generic access to the ccache. For example |
| |
| ----------------- |
| # set cache limit size |
| make CCACHE_OPTIONS="--max-size=5G" ccache-options |
| |
| # zero statistics counters |
| make CCACHE_OPTIONS="--zero-stats" ccache-options |
| ----------------- |
| |
| +ccache+ makes a hash of the source files and of the compiler options. |
| If a compiler option is different, the cached object file will not be |
| used. Many compiler options, however, contain an absolute path to the |
| staging directory. Because of this, building in a different output |
| directory would lead to many cache misses. |
| |
| To avoid this issue, buildroot has the +Use relative paths+ option |
| (+BR2_CCACHE_USE_BASEDIR+). This will rewrite all absolute paths that |
| point inside the output directory into relative paths. Thus, changing |
| the output directory no longer leads to cache misses. |
| |
| A disadvantage of the relative paths is that they also end up to be |
| relative paths in the object file. Therefore, for example, the debugger |
| will no longer find the file, unless you cd to the output directory |
| first. |
| |
| See https://ccache.samba.org/manual.html#_compiling_in_different_directories[the |
| ccache manual's section on "Compiling in different directories"] for |
| more details about this rewriting of absolute paths. |
