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From:   Fangrui Song <maskray@google.com>
Date:   Thu, 23 Mar 2023 13:01:15 -0700
Message-ID: <CAFP8O3+UO0x9aETSnOkL7=473mX0wrt+ueuB9UgOJaf+N0p7gw@mail.gmail.com>
Subject: Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        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 Wed, Mar 22, 2023 at 11:26=E2=80=AFAM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Feb 24, 2023 at 7:58=E2=80=AFAM Bj=C3=B6rn T=C3=B6pel <bjorn@kern=
el.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 ha=
ve
> > > 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?)

(I had thought about this for my own fun, but the currently only
implementation arch/arm64/kernel/head.S uses assembly.
Every port needs to write some assembly for the same task, which is a pity.
In FreeBSD rtld, glibc, and musl, DT_RELR code is target-independent.)


> >
> > Don't ask me *why*, but adding --emit-relocs to your linker flags solve=
s
> > "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/
> --
> Thanks,
> ~Nick Desaulniers
>


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