linux-kernel - Re: [PATCH v2] x86/build: fix compiler support check for CONFIG

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Message-ID: <34aa8fad-ee7f-6833-41a2-00a92b4ad369@oracle.com>
Date:   Wed, 5 Dec 2018 15:10:49 +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 v2] x86/build: fix compiler support check for
 CONFIG_RETPOLINE


On 2018/12/5 14:27, Masahiro Yamada wrote:
> It is troublesome to add a diagnostic like this to the Makefile
> parse stage because the top-level Makefile could be parsed with
> a stale include/config/auto.conf.
>
> 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
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Reported-by: Meelis Roos <mroos@...ux.ee>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
> Changes in v2:
>    - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
>    - Rephase the commit log a bit, hoping the cause of the issue will be clearer
>
>   arch/x86/Makefile | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f41..75ef499 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -220,9 +220,6 @@ 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 += $(RETPOLINE_CFLAGS)
>   endif
>   
> @@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
>   	@echo Compiler lacks asm-goto support.
>   	@exit 1
>   endif
> +ifdef CONFIG_RETPOLINE
> +ifeq ($(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
Acked-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>

-- 
Regards
Zhenzhong