Re: [PATCH] kconfig: fix extra output from savedefconfig on out-of-range defaults

[Julian Braha <julianbraha@gmail.com>]

CC: Arnd, Christophe

On 9/1/26 11:17, Geert Uytterhoeven wrote:

> FTR, this will impact all defconfigs that restrict SERIAL_8250_NR_UARTS
> to a value lower than 4:
> 
>     config SERIAL_8250_NR_UARTS
>             int "Maximum number of 8250/16550 serial ports"
>             depends on SERIAL_8250
>             default "4"
> 
>     config SERIAL_8250_RUNTIME_UARTS
>             int "Number of 8250/16550 serial ports to register at runtime"
>             depends on SERIAL_8250
>             range 0 SERIAL_8250_NR_UARTS
>             default "4"

I suspected that there could be some cases where these out-of-range
defaults were actually accidents and causing bugs, so I added a check
with my SMT solver [1], which also detected these two (powerpc-only):


  config DATA_SHIFT
    int "Data shift" if DATA_SHIFT_BOOL
    default 24 if STRICT_KERNEL_RWX && PPC64
    range 17 28 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) &&
PPC_BOOK3S_32
    range 14 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) &&
PPC_8xx
    range 20 24 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) &&
PPC_85xx
    default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
    default 18 if (DEBUG_PAGEALLOC || KFENCE) && PPC_BOOK3S_32
    default 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) &&
PPC_8xx && \
      (PIN_TLB_DATA || PIN_TLB_TEXT)
    default 19 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) &&
PPC_8xx
    default 24 if STRICT_KERNEL_RWX && PPC_85xx
    default PAGE_SHIFT

  config MODULES_SIZE
    int "Size of modules/execmem area (In Mbytes)" if MODULES_SIZE_BOOL
    range 1 256 if EXECMEM
    default 64 if EXECMEM && PPC_BOOK3S_32
    default 32 if EXECMEM && PPC_8xx
    default 0


The DATA_SHIFT case may be bug, where it should be 12, but incorrectly
adjusts to 20 when:
  PPC_85xx=y

  DEBUG_PAGEALLOC=y

  STRICT_KERNEL_RWX=n

  PAGE_SHIFT=12

The MODULES_SIZE case seems harmless since the only systems using that
option are PPC_BOOK3S_32 and PPC_8xx.

Anyway, this change to savedefconfig would also affect those 2.

[1] https://github.com/julianbraha/kconfirm/tree/smt

- Julian Braha