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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 22 Mar 2023 11:25:45 -0700
Message-ID: <CAKwvOdk0Lr-9gt0xAKvkcwA53+Wy8oeYQo1RJ7XH-LKCCURQCQ@mail.gmail.com>
Subject: Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
To:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
Cc:     Alexandre Ghiti <alex@ghiti.fr>,
        Alexandre Ghiti <alexghiti@rivosinc.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, nathan@kernel.org,
        linux-kbuild@vger.kernel.org, llvm@lists.linux.dev
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On Fri, Feb 24, 2023 at 7:58=E2=80=AFAM Bj=C3=B6rn T=C3=B6pel <bjorn@kernel=
.org> wrote:
>
> Alexandre Ghiti <alex@ghiti.fr> writes:
>
> > +cc linux-kbuild, llvm, Nathan, Nick
> >
> > On 2/15/23 15:36, Alexandre Ghiti wrote:
> >> From: Alexandre Ghiti <alex@ghiti.fr>
> >>
> > I tried a lot of things, but I struggle to understand, does anyone have
> > any idea? FYI, the same problem happens with LLVM.

Off the top of my head, no idea.

(Maybe as a follow up to this series, I wonder if pursuing
ARCH_HAS_RELR for ARCH=3Driscv is worthwhile?)

>
> Don't ask me *why*, but adding --emit-relocs to your linker flags solves
> "the NULL .rela.dyn" both for GCC and LLVM.
>
> The downside is that you end up with a bunch of .rela cruft in your
> vmlinux.

There was a patch just this week to use $(OBJCOPY) to strip these from
vmlinux (for x86). Looks like x86 uses --emit-relocs for KASLR:
https://lore.kernel.org/lkml/20230320121006.4863-1-petr.pavlu@suse.com/
--=20
Thanks,
~Nick Desaulniers