Re: [PATCH] kbuild: improve sanity check for ARCH variable on x86

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kbuild: unnormalized x86 ARCH variants force 64BIT and break defconfig
--

commit 3a5958b43dbec65a7ac36420afb7bc18b48749a2
Author: Cao Jin <pino.cao2022@gmail.com>

kbuild: improve sanity check for ARCH variable on x86

This commit replaces the explicit i386 and x86_64 checks in the top-level
Makefile with a findstring check matching "86" to set SRCARCH := x86 for
additional x86 architecture name variants such as i486, i586, i686, and
x86_32.

> diff --git a/Makefile b/Makefile
> index 8d23af898d44d..a32e20a8d41dd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -410,12 +410,10 @@ ARCH		?= $(SUBARCH)
>  UTS_MACHINE 	:= $(ARCH)
>  SRCARCH 	:= $(ARCH)
>  
> -# Additional ARCH settings for x86
> -ifeq ($(ARCH),i386)
> -        SRCARCH := x86
> -endif
> -ifeq ($(ARCH),x86_64)
> -        SRCARCH := x86
> +# Additional sanity check for cmdline ARCH settings for x86. This catch
> +# more name variants than "i386" and "x86_64".
> +ifneq ($(findstring 86,$(ARCH)),)
> +    SRCARCH := x86
>  endif

[Severity: Medium]
When make is invoked with ARCH=i486, ARCH=i586, ARCH=i686, or ARCH=x86_32,
setting SRCARCH := x86 leaves $(ARCH) unnormalized for downstream x86 build
files.

In arch/x86/Kconfig, the 64BIT symbol checks $(ARCH) directly:

config 64BIT
	bool "64-bit kernel" if "$(ARCH)" = "x86"
	default "$(ARCH)" != "i386"

Because $(ARCH) is neither "x86" nor "i386" for i486, i586, i686, and
x86_32, the prompt condition evaluates to false and the default expression
evaluates to y. Doesn't this force an unconfigurable 64-bit (CONFIG_64BIT=y,
CONFIG_X86_64=y) build when one of these 32-bit x86 ARCH variants is
requested?

Similarly, arch/x86/Makefile selects KBUILD_DEFCONFIG using $(ARCH):

ifeq ($(ARCH),x86)
  ifeq ($(shell uname -m | sed -e 's/i.86/i386/'),i386)
        KBUILD_DEFCONFIG := i386_defconfig
  else
        KBUILD_DEFCONFIG := x86_64_defconfig
  endif
else
        KBUILD_DEFCONFIG := $(ARCH)_defconfig
endif

Since arch/x86/configs/ only provides i386_defconfig and x86_64_defconfig,
won't running defconfig with ARCH=i486, ARCH=i586, ARCH=i686, or
ARCH=x86_32 still fail trying to find arch/x86/configs/$(ARCH)_defconfig?

>  
>  # Additional ARCH settings for sparc

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261020001738.2607318-1-pino.cao2022@gmail.com?part=1