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57 lines
2.2 KiB
57 lines
2.2 KiB
# Simple Kconfig recursive issue |
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# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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# |
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# Test with: |
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# |
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# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig |
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# |
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# This Kconfig file has a simple recursive dependency issue. In order to |
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# understand why this recursive dependency issue occurs lets consider what |
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# Kconfig needs to address. We iterate over what Kconfig needs to address |
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# by stepping through the questions it needs to address sequentially. |
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# |
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# * What values are possible for CORE? |
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# |
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# CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values |
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# that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y', |
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# CORE must be 'y' too. |
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# |
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# * What influences CORE_BELL_A_ADVANCED ? |
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# |
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# As the name implies CORE_BELL_A_ADVANCED is an advanced feature of |
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# CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y' |
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# we know CORE_BELL_A_ADVANCED can be 'y' too. |
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# |
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# * What influences CORE_BELL_A ? |
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# |
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# CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A. |
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# |
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# But that is a problem, because this means that in order to determine |
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# what values are possible for CORE we ended up needing to address questions |
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# regarding possible values of CORE itself again. Answering the original |
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# question of what are the possible values of CORE would make the kconfig |
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# tools run in a loop. When this happens Kconfig exits and complains about |
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# the "recursive dependency detected" error. |
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# |
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# Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be |
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# obvious that an easy to solution to this problem should just be the removal |
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# of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already |
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# since CORE_BELL_A depends on CORE. Recursive dependency issues are not always |
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# so trivial to resolve, we provide another example below of practical |
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# implications of this recursive issue where the solution is perhaps not so |
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# easy to understand. Note that matching semantics on the dependency on |
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# CORE also consist of a solution to this recursive problem. |
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mainmenu "Simple example to demo kconfig recursive dependency issue" |
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config CORE |
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tristate |
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config CORE_BELL_A |
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tristate |
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depends on CORE |
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config CORE_BELL_A_ADVANCED |
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tristate |
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depends on CORE_BELL_A |
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select CORE
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