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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /Documentation/kbuild/Kconfig.recursion-issue-01 | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/kbuild/Kconfig.recursion-issue-01')
-rw-r--r-- | Documentation/kbuild/Kconfig.recursion-issue-01 | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/Documentation/kbuild/Kconfig.recursion-issue-01 b/Documentation/kbuild/Kconfig.recursion-issue-01 new file mode 100644 index 0000000000..e8877db046 --- /dev/null +++ b/Documentation/kbuild/Kconfig.recursion-issue-01 @@ -0,0 +1,57 @@ +# Simple Kconfig recursive issue +# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +# +# Test with: +# +# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig +# +# This Kconfig file has a simple recursive dependency issue. In order to +# understand why this recursive dependency issue occurs lets consider what +# Kconfig needs to address. We iterate over what Kconfig needs to address +# by stepping through the questions it needs to address sequentially. +# +# * What values are possible for CORE? +# +# CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values +# that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y', +# CORE must be 'y' too. +# +# * What influences CORE_BELL_A_ADVANCED ? +# +# As the name implies CORE_BELL_A_ADVANCED is an advanced feature of +# CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y' +# we know CORE_BELL_A_ADVANCED can be 'y' too. +# +# * What influences CORE_BELL_A ? +# +# CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A. +# +# But that is a problem, because this means that in order to determine +# what values are possible for CORE we ended up needing to address questions +# regarding possible values of CORE itself again. Answering the original +# question of what are the possible values of CORE would make the kconfig +# tools run in a loop. When this happens Kconfig exits and complains about +# the "recursive dependency detected" error. +# +# Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be +# obvious that an easy to solution to this problem should just be the removal +# of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already +# since CORE_BELL_A depends on CORE. Recursive dependency issues are not always +# so trivial to resolve, we provide another example below of practical +# implications of this recursive issue where the solution is perhaps not so +# easy to understand. Note that matching semantics on the dependency on +# CORE also consist of a solution to this recursive problem. + +mainmenu "Simple example to demo kconfig recursive dependency issue" + +config CORE + tristate + +config CORE_BELL_A + tristate + depends on CORE + +config CORE_BELL_A_ADVANCED + tristate + depends on CORE_BELL_A + select CORE |