Re: [PATCH] [RFC] Kbuild: avoid "make tinyconfig" warnings

[Josh Triplett <josh@joshtriplett.org>]

On Wed, Jul 06, 2016 at 03:56:25PM +0200, Arnd Bergmann wrote:
> On Monday, July 4, 2016 12:58:15 PM CEST Josh Triplett wrote:
> > On Mon, Jul 04, 2016 at 12:51:56PM -0700, Josh Triplett wrote:
> > > On Mon, Jul 04, 2016 at 04:25:55PM +0200, Arnd Bergmann wrote:
> > > > The introduction of "make *.config" as a shorthand for merging configuration
> > > > files unfortunately introduced some build warnings that we see in every
> > > > single run of the various build bots testing tinyconfig:
> > > > 
> > > > .config:966:warning: override: NOHIGHMEM changes choice state
> > > > .config:965:warning: override: SLOB changes choice state
> > > > .config:963:warning: override: KERNEL_XZ changes choice state
> > > > .config:962:warning: override: CC_OPTIMIZE_FOR_SIZE changes choice state
> > > > .config:933:warning: override: SLOB changes choice state
> > > > .config:930:warning: override: CC_OPTIMIZE_FOR_SIZE changes choice state
> > > > .config:870:warning: override: SLOB changes choice state
> > > > .config:868:warning: override: KERNEL_XZ changes choice state
> > > > .config:867:warning: override: CC_OPTIMIZE_FOR_SIZE changes choice state
> > > > 
> > > > This changes the behavior for tinyconfig again, so we call the special
> > > > allnoconfig target directly, with the fragment as the KCONFIG_ALLCONFIG
> > > > file so it gets merged into the configuration. The disadvantage of
> > > > this approach is that we cannot pass another KCONFIG_ALLCONFIG on
> > > > the command line, that would again have to be done using the mergeconfig
> > > > script afterwards.
> > > > 
> > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > > > Fixes: 63a91033d52e ("kbuild: add generic mergeconfig target, %.config")
> > > > Link: https://storage.kernelci.org/mainline/v4.7-rc6/x86-tinyconfig/build.log
> > > 
> > > Thanks for fixing this.
> > > Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> > > 
> > > As another possibility, which would preserve the ability to use
> > > KCONFIG_ALLCONFIG, what about adding a parameter to mergeconfig to
> > > disable this warning?  I've seen many other uses of mergeconfig in
> > > production systems that have the same problem.
> > 
> > Actually, I just realized something: does this actually do the right
> > thing if both tiny.config files exist?  The documentation for
> > KCONFIG_ALLCONFIG doesn't suggest that it can take two files as
> > arguments.  And if it can, this also need quotes; otherwise, this will
> > expand to "... allnoconfig KCONFIG=path/to/a/tiny.config
> > another/path/to/a/tiny.config".
> 
> You are right, my patch doesn't work.
> 
> I can think of a few other ways to work around this, though none seems
> perfect:
> 
> - add a flag to the kconfig tool to ignore 'choice' symbol overrides and not
>   warn about them (as you suggested). This may be problematic if there
>   are cases in which the warning is actually helpful.

As long as this remains an option and not the default, I don't think it
would cause problems.

> - drop the feature of allowing multiple tiny.config files to be combined
>   and instead have the x86 file include everything from the architecture
>   independent file. This would only be a small annoyance, but it doesn't
>   solve the other cases you mention in which we see similar warnings.

And I'd rather not duplicate the base config into every
architecture-specific tiny.config; that'll become even more problematic
if other architectures add their own.

> - change merge_config.sh to do a 'savedefconfig' step before applying
>   the fragment, so it doesn't warn about choice statements that are
>   overridden from their default, as opposed to having conflicting choices.

This sounds like a potentially interesting approach.  This would produce
warnings only if overriding explicit configuration, but not when
changing a choice from the implicit default?

- Josh Triplett