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I previously submitted a fix for a bug in the choice feature [1], where
I mentioned, "Another (much cleaner) approach would be to remove the
tristate choice support entirely".
There are more issues in the tristate choice feature. For example, you
can observe a couple of bugs in the following test code.
[Test Code]
config MODULES
def_bool y
modules
choice
prompt "tristate choice"
default A
config A
tristate "A"
config B
tristate "B"
endchoice
Bug 1: the 'default' property is not correctly processed
'make alldefconfig' produces:
CONFIG_MODULES=y
# CONFIG_A is not set
# CONFIG_B is not set
However, the correct output should be:
CONFIG_MODULES=y
CONFIG_A=y
# CONFIG_B is not set
The unit test file, scripts/kconfig/tests/choice/alldef_expected_config,
is wrong as well.
Bug 2: choice members never get 'y' with randconfig
For the test code above, the following combinations are possible:
A B
(1) y n
(2) n y
(3) m m
(4) m n
(5) n m
(6) n n
'make randconfig' never produces (1) or (2).
These bugs are fixable, but a more critical problem is the lack of a
sensible syntax to specify the default for the tristate choice.
The default for the choice must be one of the choice members, which
cannot specify any of the patterns (3) through (6) above.
In addition, I have never seen it being used in a useful way.
The following commits removed unnecessary use of tristate choices:
- df8df5e4bc37 ("usb: get rid of 'choice' for legacy gadget drivers")
- bfb57ef0544a ("rapidio: remove choice for enumeration")
This commit removes the tristate choice support entirely, which allows
me to delete a lot of code, making further refactoring easier.
Note:
This includes the revert of commit fa64e5f6a35e ("kconfig/symbol.c:
handle choice_values that depend on 'm' symbols"). It was suspicious
because it did not address the root cause but introduced inconsistency
in visibility between choice members and other symbols.
[1]: https://lore.kernel.org/linux-kbuild/20240427104231.2728905-1-masahiroy@kernel.org/T/#m0a1bb6992581462ceca861b409bb33cb8fd7dbae
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
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Commit fbe98bb9ed3d ("kconfig: Fix defconfig when one choice menu
selects options that another choice menu depends on") fixed defconfig
when two choices interact (i.e. calculating the visibility of a choice
requires to calculate another choice).
The test code in that commit log was based on the real world example,
and complicated. So, I shrunk it down to the following:
defconfig.choice:
---8<---
CONFIG_CHOICE_VAL0=y
---8<---
---8<---
config MODULES
def_bool y
option modules
choice
prompt "Choice"
config CHOICE_VAL0
tristate "Choice 0"
config CHOICE_VAL1
tristate "Choice 1"
endchoice
choice
prompt "Another choice"
depends on CHOICE_VAL0
config DUMMY
bool "dummy"
endchoice
---8<---
Prior to commit fbe98bb9ed3d,
$ scripts/kconfig/conf --defconfig=defconfig.choice Kconfig.choice
resulted in:
CONFIG_MODULES=y
CONFIG_CHOICE_VAL0=m
# CONFIG_CHOICE_VAL1 is not set
CONFIG_DUMMY=y
where the expected result would be:
CONFIG_MODULES=y
CONFIG_CHOICE_VAL0=y
# CONFIG_CHOICE_VAL1 is not set
CONFIG_DUMMY=y
Roughly, this weird behavior happened like this:
Symbols are calculated a couple of times. First, all symbols are
calculated in conf_read(). The first 'choice' is evaluated to 'y'
due to the SYMBOL_DEF_USER flag, but sym_calc_choice() clears it
unless all of its choice values are explicitly set by the user.
conf_set_all_new_symbols() clears all SYMBOL_VALID flags. Then, only
choices are calculated. Here, the SYMBOL_DEF_USER for the first choice
has been forgotten, so it is evaluated to 'm'. set_all_choice_values()
sets SYMBOL_DEF_USER again to choice symbols.
When calculating the second choice, due to 'depends on CHOICE_VAL0',
it triggers the calculation of CHOICE_VAL0. As a result, SYMBOL_VALID
is set for CHOICE_VAL0.
Symbols except choices get the final chance of re-calculation in
conf_write(). In a normal case, CHOICE_VAL0 would be re-calculated,
then the first choice would be indirectly re-calculated with the
SYMBOL_DEF_USER which has been recalled by set_all_choice_values(),
which would be evaluated to 'y'. But, in this case, CHOICE_VAL0 has
already been marked as SYMBOL_VALID, so this re-calculation does not
happen. Then, =m from the conf_set_all_new_symbols() phase is written
out to the .config file.
Add a unit test for this naive case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>
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