Oh, now I see.   CBUILD/CHOST are not (only) about "arch", it’s (also) about "phases" and "paths".   CHOST runs (already installed) packages’ binaries.   CBUILD does everything else: fetch sources, build sources, move built binaries (i.e. "install/merge").   Thanks!   P.S. If you can, reply, please, to  https://archives.gentoo.org/gentoo-user/message/cf1cbe72d7d2337f6ebf6a29c5460c3a   Sincerely, Alexander Kurakin.