I remember when you added "module_obj" we discussed that that is an incomplete scheme and to properly calculate source paths, we would need to add an array that will contain obj/src/build dirs. Along the lines of:

  Modules []struct{
    Obj string
    Src string
    BuildSrc string
  }

If that works, it would be preferable because it extends the existing scheme to modules (implements what's currently not implemented) rather than introduces a whole new layer of complexity on top.
If it doesn't work, I would like to understand why.
Note that modules are not necessary placed relative to the kernel dir.

Actually that won't work and too complicated to support even Android different versions while the current PR implementation is much simple and support old or new OSes.

I only need to add 2 or 3 rules to fit for all modules. (even in Android S, there are two kernel trees which can be fixed by the PR with these 2 or 3 rules)

About why, there can be multiple kind of paths even inside one module. for example one module I have which can be decoded to have such file paths: (aussming kernel_src is /path_to_build/kernel_platform/common, kernel_build_src is /path_to_build/out/XXX/common)

/path_to_build/xxx/ccc.c // abosulate path for out of tree modules
Another_kernel_tree/aaa/bbb/ccc.c // relative path to another kernel tree but having Another_kernel_tree prefix
../../kernel_platform/la/ddd/ccc.c // la is a soft link to some other level of directory
../../../path_to_some_other_dir // another kind of relative path without soft link

And the clean_rules can be simple to fit for all modules, user can easily find the rules by check /rawcoverfiles or just decode the paths in all the modules/vmlinux. (Also, if there is any issue, when DoHTML shown, it will report can not open/load error for file path too).

  "clean_rules": [
     "/path_to_build/out/XXX/Another_kernel_tree/Another_kernel_tree:../../kernel_platform/Another_kernel_tree",
     "Another_kernel_tree:../../kernel_platform/Another_kernel_tree",
     "../la:../..",
     "../../..:../.."
  ],

For in-tree-module + one kernel tree (the current OSes), no impact by the PR.

And one more note is that I got 300+ modules loaded, it doesn't seem to be reasonable to add 300+ BuildSrc for modules in config.