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    Subjectkbuild: Invalid configuration generated for dependent choices by 'conf' but not by 'mconf', with reason
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    Hi,

    Consider the following Kconfig file:

    config MODULES
    def_bool y

    choice
    tristate "C1"
    config A
    tristate "A"
    config B
    tristate "B"
    endchoice

    choice
    bool "C2" if A
    config C
    bool "C"
    config D
    bool "D"
    endchoice

    When this Kconfig file is used with a configuration file containing
    just "CONFIG_A=y", conf generates the following invalid configuration:

    CONFIG_MODULES=y
    CONFIG_A=m
    # CONFIG_B is not set
    CONFIG_C=y
    # CONFIG_D is not set

    mconf on the other hand generates the correct configuration:

    CONFIG_MODULES=y
    CONFIG_A=y
    # CONFIG_B is not set
    CONFIG_C=y
    # CONFIG_D is not set

    To see this, compare the .config files generated by the following commands:

    $ scripts/kconfig/conf --defconfig=bug_config bug_Kconfig

    $ cp bug_config .config
    $ scripts/kconfig/mconf bug_Kconfig

    The root cause of the problem is the sym_calc_value(csym) call at the
    end of conf_set_all_new_symbols(). Since the second 'choice' depends
    on A, that call causes the value of A to be calculated. But this also
    causes SYMBOL_VALID to be set on A, preventing it from being
    reevaluated later when the configuration is written in conf_write().
    This reevaluation is required to get the correct value since only by
    then will the choice have SYMBOL_DEF_USER set on it (set in
    set_all_choice_values()).

    Some possible fixes:
    (1) Add another sym_clear_all_valid() call at the end of
    conf_set_all_new_symbols(). This is kinda wasteful.
    (2) Just randomize_choice_values() seems to actually need the
    sym_calc_value(csym). It could probably be moved into that function,
    perhaps doing the additional sym_clear_all_valid() there unless
    there's something neater you could do.

    It would probably be safer if someone more familiar with the
    randomization stuff wrote the actual patch.

    Linux version is 3.7.0-rc4, though this bug has likely been around a while.

    /Ulf


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