32cec3be97
by using this standard extension `adoc`, these files are rendered on gitlab & github Signed-off-by: Francois Perrad <francois.perrad@gadz.org> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
70 lines
2.9 KiB
Plaintext
70 lines
2.9 KiB
Plaintext
// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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[[ccache]]
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==== Using +ccache+ in Buildroot
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http://ccache.samba.org[ccache] is a compiler cache. It stores the
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object files resulting from each compilation process, and is able to
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skip future compilation of the same source file (with same compiler
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and same arguments) by using the pre-existing object files. When doing
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almost identical builds from scratch a number of times, it can nicely
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speed up the build process.
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+ccache+ support is integrated in Buildroot. You just have to enable
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+Enable compiler cache+ in +Build options+. This will automatically
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build +ccache+ and use it for every host and target compilation.
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The cache is located in the directory defined by the +BR2_CCACHE_DIR+
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configuration option, which defaults to
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+$HOME/.buildroot-ccache+. This default location is outside of
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Buildroot output directory so that it can be shared by separate
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Buildroot builds. If you want to get rid of the cache, simply remove
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this directory.
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You can get statistics on the cache (its size, number of hits,
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misses, etc.) by running +make ccache-stats+.
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The make target +ccache-options+ and the +CCACHE_OPTIONS+ variable
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provide more generic access to the ccache. For example
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-----------------
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# set cache limit size
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make CCACHE_OPTIONS="--max-size=5G" ccache-options
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# zero statistics counters
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make CCACHE_OPTIONS="--zero-stats" ccache-options
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-----------------
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+ccache+ makes a hash of the source files and of the compiler options.
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If a compiler option is different, the cached object file will not be
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used. Many compiler options, however, contain an absolute path to the
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staging directory. Because of this, building in a different output
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directory would lead to many cache misses.
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To avoid this issue, buildroot has the +Use relative paths+ option
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(+BR2_CCACHE_USE_BASEDIR+). This will rewrite all absolute paths that
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point inside the output directory into relative paths. Thus, changing
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the output directory no longer leads to cache misses.
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A disadvantage of the relative paths is that they also end up to be
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relative paths in the object file. Therefore, for example, the debugger
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will no longer find the file, unless you cd to the output directory
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first.
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See https://ccache.samba.org/manual.html#_compiling_in_different_directories[the
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ccache manual's section on "Compiling in different directories"] for
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more details about this rewriting of absolute paths.
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When +ccache+ is enabled in Buildroot using the +BR2_CCACHE=y+ option:
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* +ccache+ is used during the Buildroot build itself
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* +ccache+ is not used when building outside of Buildroot, for example
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when directly calling the cross-compiler or using the SDK
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One can override this behavior using the +BR2_USE_CCACHE+ environment
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variable: when set to +1+, usage of ccache is enabled (default during
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the Buildroot build), when unset or set to a value different from +1+,
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usage of ccache is disabled.
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