Re: [PATCH kernel] powerpc/makefile: Do not redefine $(CPP) for preprocessor

[Daniel Axtens <dja@axtens.net>]

Hi Alexey,

> The $(CPP) (do only preprocessing) macro is already defined in Makefile.
> However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
> in flags duplication. Which is not a big deal by itself except for
> the flags which depend on other flags and the compiler checks them
> as it parses the command line.
>
> Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
> If clang+llvm+sanitizer are enabled, this results in
> -fno-lto -flto -fsanitize=cfi-mfcall  .... -fno-lto -flto -fsanitize=cfi-mfcall

Checkpatch doesn't like this line:
WARNING:COMMIT_LOG_LONG_LINE: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#14: 
-fno-lto -flto -fsanitize=cfi-mfcall  .... -fno-lto -flto -fsanitize=cfi-mfcall
However, it doesn't make sense to wrap the line so we should just ignore
checkpatch here.

> in the clang command line and triggers error:
>
> clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
>
> This removes unnecessary CPP redifinition.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/Makefile | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index c9d2c7825cd6..3a2f2001c62b 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -214,7 +214,6 @@ KBUILD_CPPFLAGS	+= -I $(srctree)/arch/$(ARCH) $(asinstr)
>  KBUILD_AFLAGS	+= $(AFLAGS-y)
>  KBUILD_CFLAGS	+= $(call cc-option,-msoft-float)
>  KBUILD_CFLAGS	+= -pipe $(CFLAGS-y)
> -CPP		= $(CC) -E $(KBUILD_CFLAGS)

I was trying to check the history to see why powerpc has its own
definition. It seems to date back at least as far as merging the two
powerpc platforms into one, maybe it was helpful then. I agree it
doesn't seem to be needed now.

Snowpatch claims that this breaks the build, but I haven't been able to
reproduce the issue in either pmac32 or ppc64 defconfig. I have sent it
off to a fork of mpe's linux-ci repo to see if any of those builds hit
any issues: https://github.com/daxtens/linux-ci/actions

Assuming that doesn't break, this patch looks good to me:
Reviewed-by: Daniel Axtens <dja@axtens.net>

Kind regards,
Daniel