This is simple enough if you're okay with intermediary files littering the entire codebase. Targets and their intermediary files will be written right next to their sources and the whole tree will be a huge mess.

The makefile quickly gets complicated if one wants an organized source tree such as:

  source/module/file1.c
  source/module/file2.c
  source/main.c
  source/tools/tool.c

To be transformed into an architecture specific build tree whose organization automatically matches that of the source tree:

  build/$arch/prerequisites/module/file1.d
  build/$arch/prerequisites/module/file2.d
  build/$arch/prerequisites/main.d
  build/$arch/prerequisites/tools/tool.d
  build/$arch/objects/module/file1.o
  build/$arch/objects/module/file2.o
  build/$arch/objects/main.o
  build/$arch/objects/tools/tool.o
  build/$arch/executables/main
  build/$arch/executables/tool

The general solution to that is the explicit path method:

https://make.mad-scientist.net/papers/multi-architecture-bui...