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Masahiro Yamada d0e628cd81 kbuild: doc: clarify the difference between extra-y and always-y
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>
2020-12-21 13:57:07 +09:00
arch tweewide: Fix most Shebang lines 2020-12-08 23:30:04 +09:00
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Documentation kbuild: doc: clarify the difference between extra-y and always-y 2020-12-21 13:57:07 +09:00
drivers Char/Misc driver fixes for 5.10-rc7 2020-12-06 11:48:17 -08:00
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include TTY fixes for 5.10-rc7 2020-12-06 11:43:50 -08:00
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kernel A set of updates for the interrupt subsystem: 2020-12-06 11:15:55 -08:00
lib
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scripts Makefile.extrawarn: remove -Wnested-externs warning 2020-12-08 23:30:05 +09:00
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tools tweewide: Fix most Shebang lines 2020-12-08 23:30:04 +09:00
usr
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.cocciconfig
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MAINTAINERS A set of updates for the interrupt subsystem: 2020-12-06 11:15:55 -08:00
Makefile Linux 5.10-rc7 2020-12-06 14:25:12 -08:00
README

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.