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The "transitional" symbol keyword, while working with the "olddefconfig"
target, was prompting during "oldconfig". This occurred because these
symbols were not being marked as user-defined when they received values
from transitional symbols that had user values. The "olddefconfig" target
explicitly doesn't prompt for anything, so this deficiency wasn't noticed.
The issue manifested when a symbol's value came from a transitional
symbol's user value but the receiving symbol wasn't marked with
SYMBOL_DEF_USER. Thus the "oldconfig" logic would then prompt for these
symbols unnecessarily.
Check after value calculation whether a symbol without a user value
gets its value from a single transitional symbol that does have a user
value. In such cases, mark the receiving symbol as user-defined to
prevent prompting.
Update regression tests to verify that symbols with transitional defaults
are not prompted in "oldconfig", except when conditional defaults evaluate
to 'no' and should legitimately be prompted.
Build tested with "make testconfig".
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/CAHk-=wgZjUk4Cy2XgNkTrQoO8XCmNUHrTe5D519Fij1POK+3qw@mail.gmail.com/
Fixes: f9afce4f32e9 ("kconfig: Add transitional symbol attribute for migration support")
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Link: https://lore.kernel.org/r/20250930154514.it.623-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
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During kernel option migrations (e.g. CONFIG_CFI_CLANG to CONFIG_CFI),
existing .config files need to maintain backward compatibility while
preventing deprecated options from appearing in newly generated
configurations. This is challenging with existing Kconfig mechanisms
because:
1. Simply removing old options breaks existing .config files.
2. Manually listing an option as "deprecated" leaves it needlessly
visible and still writes them to new .config files.
3. Using any method to remove visibility (.e.g no 'prompt', 'if n',
etc) prevents the option from being processed at all.
Add a "transitional" attribute that creates symbols which are:
- Processed during configuration (can influence other symbols' defaults)
- Hidden from user menus (no prompts appear)
- Omitted from newly written .config files (gets migrated)
- Restricted to only having help sections (no defaults, selects, etc)
making it truly just a "prior value pass-through" option.
The transitional syntax requires a type argument and prevents type
redefinition:
config NEW_OPTION
bool "New option"
default OLD_OPTION
config OLD_OPTION
bool
transitional
help
Transitional config for OLD_OPTION migration.
This allows seamless migration: olddefconfig processes existing
CONFIG_OLD_OPTION=y settings to enable CONFIG_NEW_OPTION=y, while
CONFIG_OLD_OPTION is omitted from newly generated .config files.
Added positive and negative testing via "testconfig" make target.
Co-developed-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250923213422.1105654-2-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
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