From: Nathan Chancellor <nathan@kernel•org>
To: Alexey Kardashevskiy <aik@ozlabs•ru>, linuxppc-dev@lists•ozlabs.org
Cc: Michal Marek <michal.lkml@markovi•net>,
linux-kbuild@vger•kernel.org,
Masahiro Yamada <masahiroy@kernel•org>,
Nick Desaulniers <ndesaulniers@google•com>,
linux-kernel@vger•kernel.org, clang-built-linux@googlegroups•com
Subject: Re: [PATCH kernel v3] powerpc/makefile: Do not redefine $(CPP) for preprocessor
Date: Thu, 13 May 2021 11:59:14 -0700 [thread overview]
Message-ID: <dedc7262-2956-37b2-ebfd-ae8eb9b56716@kernel.org> (raw)
In-Reply-To: <20210513115904.519912-1-aik@ozlabs.ru>
On 5/13/2021 4:59 AM, Alexey Kardashevskiy wrote:
> 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
>
> -emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
> -fsanitize=cfi-mfcall -fno-lto ...
>
> in the clang command line and triggers error:
>
> clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
>
> This removes unnecessary CPP redefinition. Which works fine as in most
> place KBUILD_CFLAGS is passed to $CPP except
> arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
> 1. add -m(big|little)-endian to $CPP
> 2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores -m(big|little)-endian if
> the building platform does not support big endian (such as x86).
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs•ru>
> ---
> Changes:
> v3:
> * moved vdso cleanup in a separate patch
> * only add target to KBUILD_CPPFLAGS for CLANG
>
> v2:
> * fix KBUILD_CPPFLAGS
> * add CLANG_FLAGS to CPPFLAGS
> ---
> Makefile | 1 +
> arch/powerpc/Makefile | 3 ++-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 15b6476d0f89..5b545bef7653 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -576,6 +576,7 @@ CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -
> ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
> ifneq ($(CROSS_COMPILE),)
> CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> +KBUILD_CPPFLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
You can avoid the duplication here by just doing:
KBUILD_CPPFLAGS += $(CLANG_FLAGS)
I am still not super happy about the flag duplication but I am not sure
I can think of a better solution. If KBUILD_CPPFLAGS are always included
when building .o files, maybe we should just add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS instead of KBUILD_CFLAGS?
> endif
> ifeq ($(LLVM_IAS),1)
> CLANG_FLAGS += -integrated-as
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 3212d076ac6a..306bfd2797ad 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -76,6 +76,7 @@ endif
>
> ifdef CONFIG_CPU_LITTLE_ENDIAN
> KBUILD_CFLAGS += -mlittle-endian
> +KBUILD_CPPFLAGS += -mlittle-endian
> KBUILD_LDFLAGS += -EL
> LDEMULATION := lppc
> GNUTARGET := powerpcle
> @@ -83,6 +84,7 @@ 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
> @@ -208,7 +210,6 @@ 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 $(KBUILD_CFLAGS)
>
> CHECKFLAGS += -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
> ifdef CONFIG_CPU_BIG_ENDIAN
>
next prev parent reply other threads:[~2021-05-13 18:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 11:59 [PATCH kernel v3] powerpc/makefile: Do not redefine $(CPP) for preprocessor Alexey Kardashevskiy
2021-05-13 18:59 ` Nathan Chancellor [this message]
2021-05-14 1:56 ` Alexey Kardashevskiy
2021-05-14 2:42 ` Masahiro Yamada
2021-05-14 3:41 ` Alexey Kardashevskiy
2021-05-14 8:46 ` Segher Boessenkool
2021-05-17 3:23 ` Alexey Kardashevskiy
2021-05-17 19:10 ` Segher Boessenkool
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