Re: [PATCH v2] scripts: Do not strip .rela.dyn section

[Alexandre Ghiti]

On 07/04/2025 10:15, Alexandre Ghiti wrote:
> Hi Masahiro,
>
> On Fri, Apr 4, 2025 at 5:25 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> > On Fri, Apr 4, 2025 at 12:45 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
> > > Hi Ard,
> > >
> > > On 03/04/2025 17:11, Ard Biesheuvel wrote:
> > > > On Thu, 3 Apr 2025 at 16:42, Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote:
> > > > > riscv uses the .rela.dyn section to relocate the kernel at runtime but
> > > > > that section is stripped from vmlinux. That prevents kexec to
> > > > > successfully load vmlinux since it does not contain the relocations info
> > > > > needed.
> > > > Maybe explain that .rela.dyn contains runtime relocations, which are
> > > > only emitted if they are actually needed - as opposed to the static
> > > > relocations that are not emitted as SHF_ALLOC sections, and are not
> > > > considered to be part of the runtime image in the first place.
> > >
> > > Ok I'll do.
> > >
> > >
> > > > It
> > > > would be nice if we could use --remove-relocations= here, which only
> > > > removes static relocations, but unfortunately, llvm-objcopy does not
> > > > support this.
> > > >
> > > > Also, I wonder if this should apply to all of .rel.dyn, .rela.dyn and
> > > > .relr.dyn, as they all carry runtime relocations.
> > >
> > > Ok, I'll add them to the next version.
> > >
> > >
> > > > Finally, I'd be curious to know why RISC-V relies on --emit-relocs in
> > > > the first place? Is the relocs check really needed? If not, it would
> > > > be a nice opportunity to get rid of Makefile.postlink entirely.
> > >
> > > So I had to check and it happens that this was an issue with the
> > > toolchain, I should check if that still happens with newer ones.
> > >
> > > commit 559d1e45a16dcf1542e430ea3dce9ab625be98d0
> > > Author: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> > > Date:   Wed Mar 29 06:53:29 2023 +0200
> > >
> > >       riscv: Use --emit-relocs in order to move .rela.dyn in init
> >
> >
> >
> > So,
> >
> > Fixes: 559d1e45a16d ("riscv: Use --emit-relocs in order to move
> > .rela.dyn in init")
> >
> > Is this the correct tag?
> This is the initial culprit yes, but if we use this tag, the fix won't
> apply. So I decided to pick Ard's patch so that this fix can be easily
> backported to 6.14, and I'll come up with a new version for previous
> releases. Is that ok with you?


And I have just looked at 6.15-rc1 and noticed that the relocation 
stripping was moved to Makefile.vmlinux, so this fix won't apply to 6.14 
neither.

I'll then use the initial culprit, which is Fixes: 559d1e45a16d ("riscv: 
Use --emit-relocs in order to move.rela.dyn in init").

Sorry for the noise,

Alex


> Thanks,
>
> Alex
>
> > --
> > Best Regards
> > Masahiro Yamada
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