linux-kernel - Re: [PATCH] arm64: build with baremetal linker target instead of Linux when available

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Message-ID: <CAKv+Gu_TkTj5sD-FjTF=GQnNvSVNF37gCpQHxJAHy0+n=SmUbA@mail.gmail.com>
Date:   Thu, 19 Jul 2018 09:18:29 +0900
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Olof Johansson <olof@...om.net>,
        Andrew Pinski <apinski@...ium.com>,
        Yury Norov <ynorov@...iumnetworks.com>
Cc:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Kocialkowski <contact@...lk.fr>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: build with baremetal linker target instead of
 Linux when available

On 14 July 2018 at 00:30, Olof Johansson <olof@...om.net> wrote:
> Not all toolchains have the baremetal elf targets, RedHat/Fedora ones
> in particular. So, probe for whether it's available and use the previous
> (linux) targets if it isn't.
>
> Reported-by: Laura Abbott <labbott@...hat.com>
> Cc: Paul Kocialkowski <contact@...lk.fr>
> Signed-off-by: Olof Johansson <olof@...om.net>
> ---
>  arch/arm64/Makefile    | 9 +++++----
>  scripts/Kbuild.include | 4 ++--
>  2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index e7101b19d590..efe61a2e4b5e 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -60,15 +60,16 @@ ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
>  KBUILD_CPPFLAGS        += -mbig-endian
>  CHECKFLAGS     += -D__AARCH64EB__
>  AS             += -EB
> -# We must use the linux target here, since distributions don't tend to package
> -# the ELF linker scripts with binutils, and this results in a build failure.
> -LDFLAGS                += -EB -maarch64linuxb
> +# Prefer the baremetal ELF build target, but not all toolchains include
> +# it so fall back to the standard linux version if needed.
> +LDFLAGS                += -EB $(call ld-option, -maarch64elfb, -maarch64linuxb)
>  UTS_MACHINE    := aarch64_be
>  else
>  KBUILD_CPPFLAGS        += -mlittle-endian
>  CHECKFLAGS     += -D__AARCH64EL__
>  AS             += -EL
> -LDFLAGS                += -EL -maarch64linux # See comment above
> +# Same as above, prefer ELF but fall back to linux target if needed.
> +LDFLAGS                += -EL $(call ld-option, -maarch64elf, -maarch64linux)
>  UTS_MACHINE    := aarch64
>  endif
>

Did anyone check if just removing these options altogether would be an option?

The commit that introduced them does not even mention them, but only
mentions adding -mabi=lp64 to the cc/as flags:

commit 3d6a7b99e3fa29b92d6288487e057e0a596bd2b0
Author: Andrew Pinski <apinski@...ium.com>
Date:   Mon Sep 18 11:20:20 2017 +0100

    arm64: ensure the kernel is compiled for LP64

    The kernel needs to be compiled as a LP64 binary for ARM64, even when
    using a compiler that defaults to code-generation for the ILP32 ABI.
    Consequently, we need to explicitly pass '-mabi=lp64' (supported on
    gcc-4.9 and newer).

> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index c8156d61678c..1e13f502b42f 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -163,8 +163,8 @@ cc-ldoption = $(call try-run,\
>         $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>
>  # ld-option
> -# Usage: LDFLAGS += $(call ld-option, -X)
> -ld-option = $(call try-run, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2))
> +# Usage: LDFLAGS += $(call ld-option, -X, -Y)
> +ld-option = $(call try-run, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2),$(3))
>
>  # ar-option
>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
> --
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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