The CL updates the Kconfig:
1. Replace the USE_NULL_ISA with BUILD_ISA
2. The USE_XXX_ISAs are depends on BUILD_ISA
3. If the BUILD_ISA is set, at least one of USE_XXX_ISAs must be set
4. Refactor the USE_KVM option
Change-Id: I2a600dea9fb671263b0191c46c5790ebbe91a7b8
These are not yet consumed by anything, but convert all the settings
from SCons variables to Kconfig variables.
If you have existing SConsopts files which need to be converted, you
should take a look at KCONFIG.md to learn about how kconfig is used in
gem5. You should decide if any variables need to be available to C++ or
kconfig itself, and whether those are options which should be detected
automatically, or should be up to the user. Options which should be
measured automatically should still be in SConsopts files, while user
facing options should be added to new or existing Kconfig files.
Generally, make sure you're storing c++/kconfig visible options in
env['CONF'][...]. Also remove references to sticky_vars since persistent
options should now be handled with kconfig, and export_vars since
everything in env['CONF'] is now exported automatically.
Switch SCons/gem5 to use Kconfig for configuration, except EXTRAS which
is still a sticky SCons variable. This is necessary because EXTRAS also
controls what config options exist. If it came from Kconfig itself, then
there would be a circular dependency. This dependency could
theoretically be handled by reparsing the Kconfig when EXTRAS
directories were added or removed, but that would be complicated, and
isn't supported by kconfiglib. It wouldn't be worth the significant
effort it would take to add it, just to use Kconfig more purely.
Change-Id: I29ab1940b2d7b0e6635a490452d05befe5b4a2c9
