have ccache link against the same file in different directories

Question

I'm using ccache with git-worktree. So many of the same files are shared across multiple directories. Problem is that ccache doesn't check if the file is the same, and is compiled again. Is there a ccache option that would allow it to check the cache across multiple source directories?

Answer 1

ccache (by default since version 3.3) adds the current working directory to the hash if -g is used, which only makes it possible to get cache hits within the same source directory. Another similar issue is if you use absolute paths in compiler arguments, then you need to use the base_dir configuration setting.

More details from the "Compiling in different directories" section in the ccache manual:

• If you build with -g (or similar) to add debug information to the object file, you must either:

  1. use the -fdebug-prefix-map=old=new option for relocating debug info to a common prefix (e.g. -fdebug-prefix-map=$PWD=.); or
  2. set hash_dir = false.

• If you use absolute paths anywhere on the command line (e.g. the source code file path or an argument to compiler options like -I and -MF), you must to set base_dir to an absolute path to a “base directory”. ccache will then rewrite absolute paths under that directory to relative before computing the hash.