GNU make manual 翻译( 一百四十二)

5.7 Recursive Use of `make'
===========================

Recursive use of `make' means using `make' as a command in a makefile.
This technique is useful when you want separate makefiles for various
subsystems that compose a larger system.  For example, suppose you have
a subdirectory `subdir' which has its own makefile, and you would like
the containing directory's makefile to run `make' on the subdirectory.
You can do it by writing this:

     subsystem:
             cd subdir && $(MAKE)

or, equivalently, this (*note Summary of Options: Options Summary.):

     subsystem:
             $(MAKE) -C subdir
   
   You can write recursive `make' commands just by copying this example,
but there are many things to know about how they work and why, and about
how the sub-`make' relates to the top-level `make'.  You may also find
it useful to declare targets that invoke recursive `make' commands as
`.PHONY' (for more discussion on when this is useful, see *note Phony
Targets::).

   For your convenience, when GNU `make' starts (after it has processed
any `-C' options) it sets the variable `CURDIR' to the pathname of the
current working directory.  This value is never touched by `make'
again: in particular note that if you include files from other
directories the value of `CURDIR' does not change.  The value has the
same precedence it would have if it were set in the makefile (by
default, an environment variable `CURDIR' will not override this
value).  Note that setting this variable has no impact on the operation
of `make' (it does not cause `make' to change its working directory,
for example).