linux-kernel - Re: kbuild: Fail if gold linker is detected

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Date:   Tue, 16 Jul 2019 10:06:06 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        "H.J. Lu" <hjl.tools@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kbuild@...r.kernel.org
Subject: Re: kbuild: Fail if gold linker is detected

On Tue, Jul 16, 2019 at 02:47:56PM +0200, Thomas Gleixner wrote:
> The gold linker has known issues of failing the build in random and
> predictible ways. H.J. stated:
> 
>   "Since building a workable kernel for different kernel configurations
>    isn't a requirement for gold, I don't recommend gold for kernel."
> 
> So instead of dealing with attempts to duct tape gold support without
> understanding the root cause, fail the build when gold is detected.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/r/CAMe9rOqMqkQ0LNpm25yE_Yt0FKp05WmHOrwc0aRDb53miFKM+w@mail.gmail.com
> ---
>  scripts/Kconfig.include |    3 +++
>  1 file changed, 3 insertions(+)
> 
> --- a/scripts/Kconfig.include
> +++ b/scripts/Kconfig.include
> @@ -35,5 +35,8 @@ ld-option = $(success,$(LD) -v $(1))
>  $(error-if,$(failure,command -v $(CC)),compiler '$(CC)' not found)
>  $(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found)
>  
> +# Fail if the linker is gold as it's not capable of linking the kernel proper
> +$(error-if,$(success, command -v $(LD) -v | grep -q gold), gold linker '$(LD)' not supported)

Why are there two '-v' flags here? The second one is ignored since
command -v just prints out the path of the binary that is being used,
which would work in most cases but not if gold is the default system
linker.

$ command -v ld.gold -v
/usr/bin/ld.gold

$ command -v ld.gold
/usr/bin/ld.gold

$ command ld.gold -v
GNU gold (GNU Binutils 2.32) 1.16

Thus, wouldn't it be better to just call $(LD) directly, like
CC_IS_GCC and CC_IS_CLANG in init/Kconfig?

$(success, $(LD) -v | grep -q gold)

Cheers,
Nathan