linux-kernel - Re: [PATCH] x86/build: fix compiler support check for CONFIG

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Date:   Wed, 5 Dec 2018 11:22:16 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Meelis Roos <mroos@...ux.ee>, "H. Peter Anvin" <hpa@...or.com>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/build: fix compiler support check for
 CONFIG_RETPOLINE

Hi Masahiro,


Thanks for fixing.
There is a question still confusing me. There are many CONFIG_* used in 
arch/x86/Makefile.
Will they also be impacted or not?

# grep CONFIG_ arch/x86/Makefile
ifeq ($(CONFIG_X86_32),y)
         cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)
         cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)
  ......
drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
drivers-$(CONFIG_PCI)      += arch/x86/pci/
drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/
drivers-$(CONFIG_PM) += arch/x86/power/
drivers-$(CONFIG_FB) += arch/x86/video/
ifeq ($(CONFIG_X86_DECODER_SELFTEST),y)

Thanks
Zhenzhong
On 2018/12/5 11:00, Masahiro Yamada wrote:
> It is wrong to add CONFIG option diagnostic to the Makefile parse
> stage.
>
> Once you are hit by the error about non-retpoline compiler, the
> compilation still breaks even after disabling CONFIG_RETPOLINE.
>
> The easiest fix is to move this check to the "archprepare" like commit
> 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> compiler") did.
>
> Link: https://lkml.org/lkml/2018/12/4/206
> Reported-by: Meelis Roos <mroos@...ux.ee>
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
>   arch/x86/Makefile | 14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f41..ae0148b 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
>   KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>   
>   # Avoid indirect branches in kernel to deal with Spectre
> -ifdef CONFIG_RETPOLINE
> -ifeq ($(RETPOLINE_CFLAGS),)
> -  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
> -endif
> -  KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
> -endif
> +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
>   
>   archscripts: scripts_basic
>   	$(Q)$(MAKE) $(build)=arch/x86/tools relocs
> @@ -307,6 +302,13 @@ ifndef CC_HAVE_ASM_GOTO
>   	@echo Compiler lacks asm-goto support.
>   	@exit 1
>   endif
> +ifdef CONFIG_RETPOLINE
> +ifeq ($(RETPOLINE_CFLAGS),)
> +	@echo "You are building kernel with non-retpoline compiler." >&2
> +	@echo "Please update your compiler." >&2
> +	@false
> +endif
> +endif
>   
>   archclean:
>   	$(Q)rm -rf $(objtree)/arch/i386