d0e628cd81
The difference between extra-y and always-y is obscure.
Basically, Kbuild builds targets listed in extra-y and always-y in
visited Makefiles without relying on any dependency.
The difference is that extra-y is used to list the targets needed for
vmlinux whereas always-y is used to list the targets that must be always
built irrespective of final targets.
Kbuild skips extra-y when it is building only modules (i.e.
'make modules'). This is the long-standing behavior since extra-y was
introduced in 2003, and it is explained in that commit log [1].
For clarification, this is the extra-y vs always-y table:
extra-y always-y
'make' y y
'make vmlinux' y y
'make modules' n y
Kbuild skips extra-y also when building external modules since obviously
it never builds vmlinux.
Unfortunately, extra-y is wrongly used in many places of upstream code,
and even in external modules.
Using extra-y in external module Makefiles is wrong. What you should
use is probably always-y or 'targets'.
The current documentation for extra-y is misleading. I rewrote it, and
moved it to the section 3.7.
always-y is not documented anywhere. I added.
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=f94e5fd7e5d09a56a60670a9bb211a791654bba8
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.