ccache basedir doesn't work as expected

Question

I'm trying to make ccache work with the same source code built from different sibling directories. I've successfully set CCACHE_BASEDIR to the parent dir of these two siblings. If I do a build in bld1 and then switch to bld2 and build that copy (again, these are the same sources), I get no cache hits.

I'm now looking at the log output from setting CCACHE_LOGFILE. Unfortunately the log doesn't tell me what factors/data went into computing the hashes it looks up, I just see lots of "No such manifest file" message (for direct lookup, it seems).

Are there any other options I can use to debug the issue with ccache to figure out why it doesn't recognize these two source trees as identical?

Just to be clear, if I repeat the build in a given directory, I do indeed get lots of hits in the cache - so clearly ccache is working with an unchanging build path, it just doesn't seem to be working properly across directories.

Answer 1

The solution is most likely to set hash_dir = false (CCACHE_NOHASHDIR=1 if using environment variables) or setting -fdebug-prefix-map=old=new for relocating debug info to a common prefix (e.g. -fdebug-prefix-map=$PWD=.). More details can be found in the "Compiling in different directories" section in the ccache manual.