linux-kernel - Re: [PATCH v2] x86/boot: define CC_HAVE_ASM

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Message-ID: <CAGXu5jJcPm+xDuCDeMzimWto4ThpHG5+fMnmQxLbmaf8RL7EUw@mail.gmail.com>
Date:   Thu, 27 Sep 2018 14:40:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/boot: define CC_HAVE_ASM_GOTO

On Thu, Sep 27, 2018 at 1:47 PM,  <ndesaulniers@...gle.com> wrote:
> Early prototypes of Clang with asm goto support produce 6 instances of
> the following warning:
>
> In file included from arch/x86/boot/compressed/misc.h:20:
> In file included from ./include/linux/elf.h:5:
> In file included from ./arch/x86/include/asm/elf.h:8:
> In file included from ./include/linux/thread_info.h:38:
> In file included from ./arch/x86/include/asm/thread_info.h:53:
> ./arch/x86/include/asm/cpufeature.h:150:2: warning: "Compiler lacks
> ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> [-W#warnings]
> your compiler arguments"
>  ^
>
> Since 6 files under arch/x86/boot/compressed/ include
> arch/x86/boot/compressed/misc.h AND
> arch/x86/boot/compressed/Makefile happens to redefine KBUILD_CFLAGS,
> which set these variables in the top level MAKEFILE.
>
> Suggested-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> v1 -> v2:
>   Updated commit message to provide more context as per Borislav.
>
>  arch/x86/boot/compressed/Makefile | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 28764dacf018..158c0b4e178a 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -56,6 +56,13 @@ KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
>  endif
>  LDFLAGS_vmlinux := -T
>
> +# check for 'asm goto'
> +ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
> +  CC_HAVE_ASM_GOTO := 1
> +  KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
> +  KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
> +endif
> +
>  hostprogs-y    := mkpiggy
>  HOST_EXTRACFLAGS += -I$(srctree)/tools/include
>
> --
> 2.19.0.605.g01d371f741-goog
>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Pixel Security