[ccache] Feature request: Hash the compiler by version and machine
ablock at blocksoftware.net
Tue Oct 28 14:55:24 GMT 2008
I'm currently working on a project that recompiles gcc before even
starting with the actual project source. This means that in every
rebuild, large parts of the project are compiled with a freshly compiled
ccache currently checks differences in the used compiler version by
either doing a size/modification-date hash or a full hash of the
compiler binary (undocumented feature that I found). Both ways result in
a cache miss for every source file when doing a full rebuild of our project.
A solution to this would be to add a new hashing mechanism that uses the
output of "gcc -dumpversion" and "gcc -dumpmashine" to has the compiler
A maybe more secure way (to avoid wrong cache hits) would be to use the
output of "gcc --v", because it also includes the configure options used
when compiling the gcc package. Problem with this is, that the output of
--v includes absolute pathes (e.g. the --prefix option), which would
again lead to cache misses if the whole project is recompiled in a
different place. To avoid this, ccache could filter out all pathes from
the output of --v...but this again could lead to wrong cache hits in
My suggestion would be to implement both solutions and use environment
variables (as usual in ccache) to switch between the used hashing
method. Also an option that enables/disables filtering of --v would be
To Andrew (or other ccache developers):
Would you consider implementing these features? I'd be happy to do it by
myself, but I would need to know if you generally accept patches and
features from other developers.
Maybe you know a better way to fix problems like I've described above?
Either by using existing features/options or new features/options.
Thanks and greetings,
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