linux-kernel - Re: [PATCH v2 01/18] kbuild: add ld-name macro and support for GNU gold

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Date:   Wed, 15 Nov 2017 13:53:32 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Alex Matveev <alxmtvv@...il.com>, Andi Kleen <ak@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 01/18] kbuild: add ld-name macro and support for GNU gold

On Wed, Nov 15, 2017 at 1:34 PM, Sami Tolvanen <samitolvanen@...gle.com> wrote:
> GNU gold may require different flags than GNU ld. Add a macro for
> detecting the linker and conditionally add gold specific flags from
> LDFLAGS_GOLD.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

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

(It does seem weird to have only LDFLAGS instead of KBUILD_LDFLAGS,
but that's not really a problem for this patch exactly.)

-Kees

> ---
>  Makefile               | 5 +++++
>  scripts/Kbuild.include | 4 ++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/Makefile b/Makefile
> index 763ab35df12a..f976af9525bf 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -827,6 +827,11 @@ include scripts/Makefile.kasan
>  include scripts/Makefile.extrawarn
>  include scripts/Makefile.ubsan
>
> +# Add any flags specific to ld.gold
> +ifeq ($(ld-name),gold)
> +LDFLAGS                += $(LDFLAGS_GOLD)
> +endif
> +
>  # Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
>  # last assignments
>  KBUILD_CPPFLAGS += $(ARCH_CPPFLAGS) $(KCPPFLAGS)
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 9ffd3dda3889..584d6cecd7c0 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -172,6 +172,10 @@ ld-option = $(call try-run,\
>  # Important: no spaces around options
>  ar-option = $(call try-run, $(AR) rc$(1) "$$TMP",$(1),$(2))
>
> +# ld-name
> +# Expands to either bfd or gold
> +ld-name = $(shell $(LD) -v 2>&1 | grep -q "GNU gold" && echo gold || echo bfd)
> +
>  # ld-version
>  # Note this is mainly for HJ Lu's 3 number binutil versions
>  ld-version = $(shell $(LD) --version | $(srctree)/scripts/ld-version.sh)
> --
> 2.15.0.448.gf294e3d99a-goog
>



-- 
Kees Cook
Pixel Security