linux-kernel - Re: [PATCH] arm64: link with -z norelro for LLD or aarch64-elf

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Date:   Thu, 17 Dec 2020 12:01:19 +0000
From:   Will Deacon <will@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        kernel-team <kernel-team@...roid.com>,
        Peter Smith <Peter.Smith@....com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        stable <stable@...r.kernel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Fāng-ruì Sòng <maskray@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Alan Modra <amodra@...il.com>,
        "kernelci . org bot" <bot@...nelci.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: link with -z norelro for LLD or aarch64-elf

On Wed, Dec 16, 2020 at 04:40:51PM -0800, Nick Desaulniers wrote:
> With newer GNU binutils, linking with BFD produces warnings for vmlinux:
> aarch64-linux-gnu-ld: warning: -z norelro ignored
> 
> BFD can produce this warning when the target emulation mode does not
> support RELRO relocation types, and -z relro or -z norelro is passed.
> 
> Alan Modra clarifies:
>   The default linker emulation for an aarch64-linux ld.bfd is
>   -maarch64linux, the default for an aarch64-elf linker is
>   -maarch64elf.  They are not equivalent.  If you choose -maarch64elf
>   you get an emulation that doesn't support -z relro.
> 
> The ARCH=arm64 kernel prefers -maarch64elf, but may fall back to
> -maarch64linux based on the toolchain configuration.
> 
> LLD will always create RELRO relocation types regardless of target
> emulation.
> 
> To avoid the above warning when linking with BFD, pass -z norelro only
> when linking with LLD or with -maarch64linux.

Given that, prior to 3b92fa7485eb, we used to pass '-z norelro' if
CONFIG_RELOCATABLE then was this already broken with the ELF toolchain?

Will