Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections - Jean-Philippe Brucker

From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Ingo Molnar <mingo@redhat.com>, James Morse <james.morse@arm.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Borislav Petkov <bp@suse.de>,
	Peter Collingbourne <pcc@google.com>,
	Ingo Molnar <mingo@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections
Date: Tue, 27 Oct 2020 11:08:44 +0100	[thread overview]
Message-ID: <20201027100844.GA1514990@myrica> (raw)
In-Reply-To: <CAMj1kXHXk3BX6mz6X_03sj_pSLj9Ck-=1S57tV3__N9JQOcDEw@mail.gmail.com>

Hi,

On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote:
> > > > Note that even on plain be2881824ae9eb92, I get:
> > > >
> > > >     aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
> > > >     aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
> > > >
> > > > The parent commit obviously doesn't show that (but probably still has
> > > > the problem).
> >
> > Reverting both
> > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement")
> > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections")
> > seems to solve my problems, without any ill effects?
> >
> 
> I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0)

I have the same problem with one of my debug configs and Linux v5.10-rc1,
and can reproduce with the Debian 8.3.0 toolchain, by using the arm64
defconfig and disabling CONFIG_MODULES:

ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group
ld: Unexpected GOT/PLT entries detected!
ld: Unexpected run-time procedure linkages detected!

Adding -fno-pie to this command doesn't fix the problem.

Note that when cross-building with a GCC 10.2 and binutils 2.35.1 I also
get several "aarch64-linux-gnu-ld: warning: -z norelro ignored" in
addition to the error, but I don't get that warning with the 8.3.0
toolchain.

Thanks,
Jean

> 
> The presence of .data.rel.ro and .got.plt sections suggests that the
> toolchain is using -fpie and/or -z relro to build shared objects
> rather than a fully linked bare metal binary.
> 
> Which toolchain are you using? Does adding -fno-pie to the compiler
> command line and/or adding -z norelro to the linker command line make
> any difference?
> 
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