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From: Ard Biesheuvel <ardb@kernel.org>
To: sedat.dilek@gmail.com
Cc: Kees Cook <keescook@chromium.org>,
	Fangrui Song <maskray@google.com>, X86 ML <x86@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	linux-efi <linux-efi@vger.kernel.org>,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	kbuild test robot <lkp@intel.com>
Subject: Re: [PATCH] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
Date: Fri, 22 May 2020 17:59:35 +0200
Message-ID: <CAMj1kXG0qbg-hs1Hj1ER1bMidAMjh1voaOdoCh-zhQ+QgVhy5w@mail.gmail.com> (raw)
In-Reply-To: <CA+icZUXmuJ8rka7zvGRV=eb3tdi_ro5R33o=yncGhRJ2DtB5=Q@mail.gmail.com>

On Fri, 22 May 2020 at 17:57, Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Fri, May 22, 2020 at 5:54 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Fri, 22 May 2020 at 08:51, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > On Fri, May 22, 2020 at 4:43 AM Kees Cook <keescook@chromium.org> wrote:
> > > >
> > > > On Wed, May 20, 2020 at 11:20:10AM -0700, 'Fangrui Song' via Clang Built Linux wrote:
> > > > > In the latest efi tree, ce5e3f909fc0ed67e58367b9c56a54c20a51080b
> > > > > "efi/printf: Add 64-bit and 8-bit integer support",
> > > > > arch/x86/boot/compressed/vmlinux may have an undesired
> > > > > .discard.unreachable section from drivers/firmware/efi/libstub/vsprintf.stub.o
> > > > >
> > > > > .discard.unreachable contains an R_X86_64_PC32 relocation, which will be
> > > > > warned by LLD: a non-SHF_ALLOC section (.discard.unreachable) is not
> > > > > part of the memory image, thus conceptually the distance between a
> > > > > non-SHF_ALLOC and a SHF_ALLOC is not a constant which can be resolved at
> > > > > link time.
> > > > >
> > > > > % ld.lld -m elf_x86_64 -T arch/x86/boot/compressed/vmlinux.lds ... -o arch/x86/boot/compressed/vmlinux
> > > > > ld.lld: warning: vsprintf.c:(.discard.unreachable+0x0): has non-ABS relocation R_X86_64_PC32 against symbol ''
> > > > >
> > > > > Reuse the DISCARDS macro which includes .discard.* to drop .discard.unreachable
> > > > >
> > > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > > > Signed-off-by: Fangrui Song <maskray@google.com>
> > > >
> > > > Yay macro usage! :)
> > > >
> > > > Reviewed-by: Kees Cook <keescook@chromium.org>
> > > >
> > >
> > > Feel free to add...
> > >
> > >    Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # build and boot on
> > > Linux v5.7-rc6+ with Clang and LLD v10.0.1-rc1
> > >
> > > ...together with one more patches in the x86/boot area:
> > >
> > > x86/boot: Correct relocation destination on old linkers
> > >
> > > Next run will include:
> > >
> > > x86/boot: Add .text.startup to setup.ld (v2)
> > >
> > > - Sedat -
> > >
> > > [1] https://github.com/llvm/llvm-project/releases/tag/llvmorg-10.0.1-rc1
> >
> > Thanks, I'll queue this up.
>
> Just FYI:
> It's in tip.git#x86/build already.
>
> - Sedat -
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/build&id=d6ee6529436a15a0541aff6e1697989ee7dc2c44

Thanks for the head's up. I'll remove it from my branch again.

      reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-20 18:20 Fangrui Song
2020-05-20 19:19 ` Arvind Sankar
2020-05-22  2:42 ` Kees Cook
2020-05-22  6:51   ` Sedat Dilek
2020-05-22 15:54     ` Ard Biesheuvel
2020-05-22 15:57       ` Sedat Dilek
2020-05-22 15:59         ` Ard Biesheuvel [this message]

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