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- // -*- 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.
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