kconfig: report select on a depending option

kconfig: report select on a depending option

[Jan Engelhardt]

Hi,


With the following combination of Kconfig config options, I can select 
TEST_Z, which will select TEST_X, even if TEST_Y=n. It also allows for 
awkward situations like TEST_Y=M, TEST_X=y, TEST_Z=y, which would yield 
a link time error when X uses Y's symbols.
Is there a way to have such potential errors reported with kconfig?

config TEST_Y
	tristate "Y"

config TEST_X
	depends on Y
	tristate "X"

config TEST_Z
	select TEST_Y
	tristate "Z"

thanks,
Jan

Re: kconfig: report select on a depending option

[Américo Wang]

On Thu, Mar 18, 2010 at 5:21 PM, Jan Engelhardt <jengelh@medozas.de> wrote:
> Hi,
>
>
> With the following combination of Kconfig config options, I can select
> TEST_Z, which will select TEST_X, even if TEST_Y=n. It also allows for
> awkward situations like TEST_Y=M, TEST_X=y, TEST_Z=y, which would yield
> a link time error when X uses Y's symbols.
> Is there a way to have such potential errors reported with kconfig?
>
> config TEST_Y
>        tristate "Y"
>
> config TEST_X
>        depends on Y
>        tristate "X"
>
> config TEST_Z
>        select TEST_Y

You mean "select TEST_X" here, right?

>        tristate "Z"
>

I think you should use "depends on X" instead of "select X".

Re: kconfig: report select on a depending option

[Michal Marek]

On 18.3.2010 10:21, Jan Engelhardt wrote:
> Hi,
> 
> 
> With the following combination of Kconfig config options, I can select 
> TEST_Z, which will select TEST_X, even if TEST_Y=n. It also allows for 
> awkward situations like TEST_Y=M, TEST_X=y, TEST_Z=y, which would yield 
> a link time error when X uses Y's symbols.

That's a known bug unfortunatelly
(Documentation/kbuild/kconfig-language.txt):
  Note:
        select should be used with care. select will force
        a symbol to a value without visiting the dependencies.
        By abusing select you are able to select a symbol FOO even
        if FOO depends on BAR that is not set.
        In general use select only for non-visible symbols
        (no prompts anywhere) and for symbols with no dependencies.
        That will limit the usefulness but on the other hand avoid
        the illegal configurations all over.
        kconfig should one day warn about such things.



> Is there a way to have such potential errors reported with kconfig?

No there isn't. There is a guy who wants to work on improving/rewriting
the kconfig depsolver during GSoC, let's see :). But a warning should be
easy to add now, I think.

Michal