Re: [PATCH 1/2] kbuild: Move testing of '-mfentry' back to Makefile from Kconfig

[sashiko-bot@kernel.org]

> Unlike cc-option in Kbuild, cc-option in Kconfig does not test options
> with either bit ('-m32' / '-m64') or endianness ('-mbig-endian' /
> '-mlittle-endian') flags because which flag to use may depend on the
> result of the configuration stage. This difference changes the result of
> testing for '-mfentry' support when using the kernel.org s390 cross
> compiler, which is configured for 32-bit by default.
> 
>   $ s390-linux-gcc -mfentry -o /dev/null -x c -c /dev/null
>   cc1: error: '-mfentry' is supported only for 64-bit CPUs
> 
> arch/s390/Makefile sets '-m64' in KBUILD_CPPFLAGS early, so '-mfentry'
> support was properly tested before the move to Kconfig.
> 
>   $ s390-linux-gcc -m64 -mfentry -o /dev/null -x c -c /dev/null
> 
> Ricardo reported another issue with moving this check from Kbuild to
> Kconfig, as '-mfentry' is not supported for x86_32 without '-fno-pic',
> which affects GCC builds that are configured with PIE enabled by
> default. arch/x86/Makefile adds '-fno-pic' to KBUILD_CFLAGS, so this
> works properly in Kbuild.
> 
> Move the '-mfentry' check back into Kbuild to avoid adding additional
> complexity to the Kconfig entry.
> 
> Fixes: 454e00cf8ee5 ("kbuild: avoid re-running compiler and linker probes")
> Reported-by: Ricardo Ribalda <ribalda@chromium.org>
> Closes: https://lore.kernel.org/20261020-pie-v1-1-9be09f2324b1@chromium.org/
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261020-kconfig-fix-mfentry-check-v1-0-428258bc0fc0@kernel.org?part=1