linux-kernel - Re: [PATCH] kbuild: hdrcheck: fix cross build with clang

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Message-ID: <20250221212603.GA3561672@ax162>
Date: Fri, 21 Feb 2025 13:26:03 -0800
From: Nathan Chancellor <nathan@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Nicolas Schier <nicolas@...sle.eu>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH] kbuild: hdrcheck: fix cross build with clang

On Fri, Feb 21, 2025 at 10:20:07PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The headercheck tries to call clang with a mix of compiler arguments
> that don't include the target architecture. When building e.g. x86
> headers on arm64, this produces a warning like
> 
>    clang: warning: unknown platform, assuming -mfloat-abi=soft
> 
> Add in the CLANG_FLAGS, which contain the target, in order to make it
> build properly.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

This looks like a similar problem as the one fixed by
commit 1b71c2fb04e7 ("kbuild: userprogs: fix bitsize and target
detection on clang"), should it be addressed in the same manner
(especially since I think the Fixes commit would be the same)? Given
that the filter expression is the same, maybe it would be possible to
unify them but that could happen as a follow up.

> ---
>  usr/include/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/usr/include/Makefile b/usr/include/Makefile
> index 58a9cbe4eba4..99f9e904adcd 100644
> --- a/usr/include/Makefile
> +++ b/usr/include/Makefile
> @@ -10,7 +10,7 @@ UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration
>  
>  # In theory, we do not care -m32 or -m64 for header compile tests.
>  # It is here just because CONFIG_CC_CAN_LINK is tested with -m32 or -m64.
> -UAPI_CFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
> +UAPI_CFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS) $(CLANG_FLAGS))
>  
>  # USERCFLAGS might contain sysroot location for CC.
>  UAPI_CFLAGS += $(USERCFLAGS)
> -- 
> 2.39.5
>