linux-kernel - Re: [PATCH] powerpc: vdso: fix building with wrong-endian toolchain

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Date: Fri, 7 Jun 2024 07:43:29 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Michael Ellerman <mpe@...erman.id.au>, Arnd Bergmann <arnd@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>, linux-kbuild@...r.kernel.org,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: vdso: fix building with wrong-endian toolchain

On Fri, Jun 07, 2024 at 04:11:25PM +0200, Arnd Bergmann wrote:
> This patch seems to work as well for me, and is a little
> more logical, but it's also more invasive and has a
> higher regression risk:

Commit feb843a469fb ("kbuild: add $(CLANG_FLAGS) to KBUILD_CPPFLAGS")
did something similar for clang for the same reason, so I would say it
is worth pursuing this direction. It also avoids including KBUILD_CFLAGS
twice when generating .i files.

Cheers,
Nathan

> 8<---------
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 65261cbe5bfd..9ad4ca318e34 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -62,14 +62,14 @@ KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
>  endif
>  
>  ifdef CONFIG_CPU_LITTLE_ENDIAN
> -KBUILD_CFLAGS  += -mlittle-endian
> +KBUILD_CPPFLAGS        += -mlittle-endian
>  KBUILD_LDFLAGS += -EL
>  LDEMULATION    := lppc
>  GNUTARGET      := powerpcle
>  MULTIPLEWORD   := -mno-multiple
>  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-save-toc-indirect)
>  else
> -KBUILD_CFLAGS += $(call cc-option,-mbig-endian)
> +KBUILD_CPPFLAGS += $(call cc-option,-mbig-endian)
>  KBUILD_LDFLAGS += -EB
>  LDEMULATION    := ppc
>  GNUTARGET      := powerpc
> @@ -95,7 +95,7 @@ aflags-$(CONFIG_CPU_BIG_ENDIAN)               += $(call cc-option,-mbig-endian)
>  aflags-$(CONFIG_CPU_LITTLE_ENDIAN)     += -mlittle-endian
>  
>  ifeq ($(HAS_BIARCH),y)
> -KBUILD_CFLAGS  += -m$(BITS)
> +KBUILD_CPPFLAGS        += -m$(BITS)
>  KBUILD_AFLAGS  += -m$(BITS)
>  KBUILD_LDFLAGS += -m elf$(BITS)$(LDEMULATION)
>  endif
> @@ -176,7 +176,6 @@ KBUILD_CPPFLAGS     += -I $(srctree)/arch/powerpc $(asinstr)
>  KBUILD_AFLAGS  += $(AFLAGS-y)
>  KBUILD_CFLAGS  += $(call cc-option,-msoft-float)
>  KBUILD_CFLAGS  += $(CFLAGS-y)
> -CPP            = $(CC) -E $(KBUILD_CFLAGS)
>  
>  CHECKFLAGS     += -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
>  ifdef CONFIG_CPU_BIG_ENDIAN
> diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
> index 1b93655c2857..3516e71926e5 100644
> --- a/arch/powerpc/kernel/vdso/Makefile
> +++ b/arch/powerpc/kernel/vdso/Makefile
> @@ -59,7 +59,7 @@ ldflags-$(CONFIG_LD_IS_LLD) += $(call cc-option,--ld-path=$(LD),-fuse-ld=lld)
>  ldflags-$(CONFIG_LD_ORPHAN_WARN) += -Wl,--orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
>  
>  # Filter flags that clang will warn are unused for linking
> -ldflags-y += $(filter-out $(CC_AUTO_VAR_INIT_ZERO_ENABLER) $(CC_FLAGS_FTRACE) -Wa$(comma)%, $(KBUILD_CFLAGS))
> +ldflags-y += $(filter-out $(CC_AUTO_VAR_INIT_ZERO_ENABLER) $(CC_FLAGS_FTRACE) -Wa$(comma)%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
>  
>  CC32FLAGS := -m32
>  LD32FLAGS := -Wl,-soname=linux-vdso32.so.1
> --------->8
> 
>      Arnd