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SubjectRe: [PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE
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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@linux.ee>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.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@oracle.com>

--
Regards
Zhenzhong

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