Re: [PATCH 1/2] Makefile: Strip leading spaces when preprocessing generated_defconfig

[Yao Zi <ziyao@disroot.org>]

On Sun, Apr 27, 2025 at 05:19:04PM +0200, Heinrich Schuchardt wrote:
> Am 27. April 2025 16:50:10 MESZ schrieb Yao Zi <ziyao@disroot.org>:
> >Clang's preprocessor may emit extra spaces for lines starting with '#'.
> >Lines with these extra characters cannot be handled by Kconfig and will
> >be ignored with warnings like,
> >
> 
> 
> Do you have an example for reprocing the issue?

Sure,

	clang-19 -E -nostdinc -P -I . -undef -x assembler-with-cpp \
		configs/starfive_visionfive2_defconfig

or a smaller example for demonstrating the behaviour,

	cat << EOF | clang -E -P -x assembler-with-cpp -
	# comment line
	normal line
	EOF

and you could see the strange indentation. For reproducing the exact
Kconfig warnings,

	make ARCH=riscv \
		CC='clang-19 --target=riscv64-unknown-linux-musl' \
		starfive_visionfive2_defconfig

(Clang is called clang-19 on my machine)

> Is there an understanding why Clang behaves in this way?

Sadly I have no idea. I guess it may serve for improving
human-readability of the preprocessed output.

This piece of Makefile (processing defconfigs with C preprocessor) is
U-Boot specific and doesn't exist in Linux kernel, thus it's unlikely
to have someone noted the bahaviour difference of preprocessors before.

Honestly saying sedding the output isn't a clean solution, but I cannot
come up with a better way. It'll be nice to have a flag to control the
format of output, but I didn't find one.

Am looking forward to further suggestions and documentation on this.

> Best regards 
> 
> Heinrich 

Thanks,
Yao Zi

> >        unexpected data:  # CONFIG_OF_BOARD_FIXUP is not set
> >
> >Those options that is expected to be assigned explicitly with N will be
> >set to the default value, messing up board configurations.
> >
> >Let's sed these spaces away to ensure board configurations could be
> >correctly generated with Clang.
> >
> >Fixes: 2027e99e61a ("Makefile: Run defconfig files through the C preprocessor")
> >Reported-by: Nathaniel Hourt <I@nathaniel.land>
> >Signed-off-by: Yao Zi <ziyao@disroot.org>
> >---
> > scripts/kconfig/Makefile | 1 +
> > 1 file changed, 1 insertion(+)
> >
> >diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
> >index 079add4d5da..ba30652f01a 100644
> >--- a/scripts/kconfig/Makefile
> >+++ b/scripts/kconfig/Makefile
> >@@ -94,6 +94,7 @@ endif
> > 
> > %_defconfig: $(obj)/conf
> > 	$(Q)$(CPP) -nostdinc -P -I $(srctree) -undef -x assembler-with-cpp $(srctree)/arch/$(SRCARCH)/configs/$@ -o generated_defconfig
> >+	$(Q)sed -i -e 's/^[[:space:]]//' generated_defconfig
> > 	$(Q)$< $(silent) --defconfig=generated_defconfig $(Kconfig)
> > 
> > # Added for U-Boot (backward compatibility)
>