[U-Boot] in Kbuild, what is the difference between "extra-" and "obj-"?

[Robert P. J. Day]

  admittedly, this is more a kernel Kbuild question, but in
common/Makefile, i see the snippet:

extra-$(CONFIG_ENV_IS_EMBEDDED) += env_embedded.o
obj-$(CONFIG_ENV_IS_IN_EEPROM) += env_embedded.o
extra-$(CONFIG_ENV_IS_IN_FLASH) += env_embedded.o

what is the functional difference between using "extra-" and "obj-" in
the above? those three lines look ... inconsistent?

  anyway, what is going on there? thanks.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================