Date:   Thu, 21 May 2020 19:42:55 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Fangrui Song <maskray@google.com>
Cc:     x86@kernel.org, Arvind Sankar <nivedita@alum.mit.edu>,
        linux-efi@vger.kernel.org, clang-built-linux@googlegroups.com,
        Nick Desaulniers <ndesaulniers@google.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        kbuild test robot <lkp@intel.com>
Subject: Re: [PATCH] x86/boot: Discard .discard.unreachable for
 arch/x86/boot/compressed/vmlinux
Message-ID: <202005211942.6E5061433@keescook>
References: <20200520182010.242489-1-maskray@google.com>
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In-Reply-To: <20200520182010.242489-1-maskray@google.com>
Sender: linux-efi-owner@vger.kernel.org
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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>

-- 
Kees Cook