I've been trying this for a few days and now noticed u-boot no longer builds with an output dir ( `make O=subdir whatever` ).
It sure took me ages to figure it was CDPATH, but CDPATH it is. I won't retry without making that "cd @" thing a subfunction (that might involve making its own completion, but that's easy compared to debugging make... I still don't know WHY it broke, just that it's CDPATH that broke it -- it decided to duplicate the subdir arg when invoking a submake so make was now left with a weird unknown target, but it obviously wouldn't say that and just failed weirdly)
Interesting, thanks for sharing. I would be tempted to call this a bug in the Makefile if this is the case. CDPATH is a standard bash environment variable, people use it in various ways: https://github.com/search?q=%22export+CDPATH%22&type=code
If all these causes the build to fail then the maintainers of that build should be informed.
It sure took me ages to figure it was CDPATH, but CDPATH it is. I won't retry without making that "cd @" thing a subfunction (that might involve making its own completion, but that's easy compared to debugging make... I still don't know WHY it broke, just that it's CDPATH that broke it -- it decided to duplicate the subdir arg when invoking a submake so make was now left with a weird unknown target, but it obviously wouldn't say that and just failed weirdly)