Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20200405082451.694910-1-jiaxun.yang@flygoat.com> <20200407080611.859256-1-jiaxun.yang@flygoat.com>
In-Reply-To: <20200407080611.859256-1-jiaxun.yang@flygoat.com>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 7 Apr 2020 10:21:56 -0700
Message-ID: <CAKwvOd=Upj_OcrhBnqf1=woCRm-g2wqjv882R0HQeMJu12Uq9w@mail.gmail.com>
Subject: Re: [PATCH v2] MIPS: Truncate load-y into 32bit for 32bit kernel
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     linux-mips@vger.kernel.org,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Fangrui Song <maskray@google.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Apr 7, 2020 at 1:07 AM Jiaxun Yang <jiaxun.yang@flygoat.com> wrote:
>
> LLD failed to link vmlinux with 64bit load address for 32bit ELF
> while bfd will strip 64bit address into 32bit silently.
> To fix LLD build, we should truncate load address provided by platform
> into 32bit for 32bit kernel.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> Reviewed-by: Fangrui Song <maskray@google.com>
> Tested-by: Nathan Chancellor <natechancellor@gmail.com>
>
> --
> V2: Take MaskRay's shell magic.

V2 is way too clever, V1 was much more readable.

Can this tag be added to the commit to help us track when and where it lands?
Link: https://github.com/ClangBuiltLinux/linux/issues/786

> ---
>  arch/mips/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index e1c44aed8156..f8fd3c39fb55 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -286,6 +286,9 @@ ifdef CONFIG_64BIT
>        $(error CONFIG_CPU_DADDI_WORKAROUNDS unsupported without -msym32)
>      endif
>    endif
> +else
> +       # Truncate address into 32-bit
> +       load-y := 0x$(shell echo "$(load-y)" | rev | head -c 8 | rev)
>  endif
>
>  KBUILD_AFLAGS  += $(cflags-y)
> --

-- 
Thanks,
~Nick Desaulniers