Explain the Makefile generated by mkmakefile (Linux kernel, buildroot, busybox)
===

The script mkmakefile generates the following Makefile in the builddir.

If invoked all targets are passed to the srcdir Makefile.

Can anyone explain why? Where is the magic?

<pre>
lastword = $(word $(words $(1)),$(1))
makedir := $(dir $(call lastword,\$(MAKEFILE_LIST)))

MAKEARGS := -C path_to_srcdir
MAKEARGS += O=$(if $(patsubst /%,,$(makedir)),$(CURDIR)/)$(patsubst %/,%,$(makedir))

MAKEFLAGS += --no-print-directory

.PHONY: all $(MAKECMDGOALS)

all	:= $(filter-out all Makefile,$(MAKECMDGOALS))

all:
	$(MAKE) $(MAKEARGS) $(all)

Makefile:;

$(all): all
	@:

%/: all
	@:
</pre>