linux-kernel - Re: [PATCH v5 2/4] riscv: Introduce CONFIG

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Message-ID: <b588dd9e-dff8-3458-0c7d-149e3990bca7@forissier.org>
Date:   Wed, 10 Jun 2020 16:10:24 +0200
From:   Jerome Forissier <jerome@...issier.org>
To:     Alexandre Ghiti <alex@...ti.fr>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <Anup.Patel@....com>,
        Atish Patra <Atish.Patra@....com>,
        Zong Li <zong.li@...ive.com>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org
Cc:     Anup Patel <anup@...infault.org>
Subject: Re: [PATCH v5 2/4] riscv: Introduce CONFIG_RELOCATABLE



On 6/7/20 9:59 AM, Alexandre Ghiti wrote:
[...]

> +config RELOCATABLE
> +	bool
> +	depends on MMU
> +	help
> +          This builds a kernel as a Position Independent Executable (PIE),
> +          which retains all relocation metadata required to relocate the
> +          kernel binary at runtime to a different virtual address than the
> +          address it was linked at.
> +          Since RISCV uses the RELA relocation format, this requires a
> +          relocation pass at runtime even if the kernel is loaded at the
> +          same address it was linked at.

Is this true? I thought that the GNU linker would write the "proper"
values by default, contrary to the LLVM linker (ld.lld) which would need
a special flag: --apply-dynamic-relocs (by default the relocated places
are set to zero). At least, it is my experience with Aarch64 on a
different project. So, sorry if I'm talking nonsense here -- I have not
looked at the details.

-- 
Jerome