linux-kernel - Re: [PATCH v3 0/7] x86: Refactor and consolidate startup code

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Message-ID: <CAMj1kXEbLAUMSHe9uYGdtorTr7UBFiU6DHBhfzQjMs1QGLXXwQ@mail.gmail.com>
Date: Wed, 9 Apr 2025 08:47:45 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-efi@...r.kernel.org, x86@...nel.org, mingo@...nel.org, 
	linux-kernel@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>, 
	Dionna Amalie Glaze <dionnaglaze@...gle.com>, Kevin Loughlin <kevinloughlin@...gle.com>
Subject: Re: [PATCH v3 0/7] x86: Refactor and consolidate startup code

On Tue, 8 Apr 2025 at 20:16, Brian Gerst <brgerst@...il.com> wrote:
>
> On Tue, Apr 8, 2025 at 5:01 AM Ard Biesheuvel <ardb+git@...gle.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > Reorganize C code that is used during early boot, either in the
> > decompressor/EFI stub or the kernel proper, but before the kernel
> > virtual mapping is up.
> >
> > v3:
> > - keep rip_rel_ptr() around in PIC code - sadly, it is still needed in
> >   some cases
> > - remove RIP_REL_REF() uses in separate patches
> > - keep __head annotations for now, they will all be removed later
> > - disable objtool validation for library objects (i.e., pieces that are
> >   not linked into vmlinux)
> >
> > I will follow up with a series that gets rid of .head.text altogether,
> > as it will no longer be needed at all once the startup code is checked
> > for absolute relocations.
> >
> > The SEV startup code needs to be moved first, though, and this is a bit
> > more complicated, so I will decouple that effort from this series, also
> > because there is a known issue that needs to be fixed first related to
> > memory acceptance from the EFI stub.
>
> Is there anything to verify that the compiler doesn't do something
> unexpected with PIC code generation like create GOT references?
>

I will propose something along the lines of what is already being done
for the EFI stub:

------%<------

STUBCOPY_RELOC-$(CONFIG_X86_64) := R_X86_64_64

quiet_cmd_stubcopy = STUBCPY $@
      cmd_stubcopy =                                                    \
        $(STRIP) --strip-debug -o $@ $<;                                \
        if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then            \
                echo "$@: absolute symbol references not allowed in
the EFI stub" >&2; \
                /bin/false;                                             \
        fi;                                                             \
        $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@