linux/Documentation/kbuild
Masahiro Yamada 45c7f555bf kconfig: doc: document behavior of 'select' and 'imply' followed by 'if'
Documentation/kbuild/kconfig-language.rst explains the behavior of
'select' as follows:

  reverse dependencies can be used to force a lower limit of
  another symbol. The value of the current menu symbol is used as the
  minimal value <symbol> can be set to.

This is not true when the 'select' property is followed by 'if'.

[Test Code]

    config MODULES
            def_bool y
            modules

    config A
            def_tristate y
            select C if B

    config B
            def_tristate m

    config C
            tristate

[Result]

    CONFIG_MODULES=y
    CONFIG_A=y
    CONFIG_B=m
    CONFIG_C=m

If "the value of A is used as the minimal value C can be set to",
C must be 'y'.

The actual behavior is "C is selected by (A && B)". The lower limit of
C is downgraded due to B being 'm'.

This behavior is kind of weird, and this has arisen several times in
the mailing list.

I do not know whether it is a bug or intended behavior. Anyway, it is
not feasible to change it now because many Kconfig files are written
based on this behavior. The same applies to 'imply'.

Document this (but reserve the possibility for a future change).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
2024-06-06 20:05:15 +09:00
..
gcc-plugins.rst docs/core-api: expand Fedora instructions for GCC plugins 2022-09-27 13:21:44 -06:00
headers_install.rst Kbuild updates for v5.3 2019-07-12 16:03:16 -07:00
index.rst Kbuild updates for v5.7 2020-03-31 16:03:39 -07:00
issues.rst docs: kbuild: fix build with pdf and fix some minor issues 2019-07-15 11:03:04 -03:00
kbuild.rst docs: kbuild: add INSTALL_DTBS_PATH 2023-10-18 17:16:09 +09:00
kconfig-language.rst kconfig: doc: document behavior of 'select' and 'imply' followed by 'if' 2024-06-06 20:05:15 +09:00
kconfig-macro-language.rst kconfig: doc: fix $(fileno) to $(filename) 2020-12-21 16:01:44 +09:00
Kconfig.recursion-issue-01 docs: kconfig: Fix grammar and formatting 2024-02-15 06:55:47 +09:00
Kconfig.recursion-issue-02 docs: use the lore redirector everywhere 2021-10-12 13:58:19 -06:00
kconfig.rst docs: kbuild/kconfig: reformat/cleanup 2024-02-19 18:20:39 +09:00
Kconfig.select-break kbuild: document recursive dependency limitation / resolution 2015-10-08 15:36:16 +02:00
llvm.rst Documentation/llvm: Note s390 LLVM=1 support with LLVM 18.1.0 and newer 2024-03-31 21:09:50 +09:00
makefiles.rst kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
modules.rst kbuild: doc: replace arch/$(ARCH)/ with arch/$(SRCARCH)/ 2020-12-21 13:56:58 +09:00
reproducible-builds.rst Documentation: kbuild: Add description of git for reproducible builds 2022-10-28 00:16:29 +09:00