Re: [PATCH] arm64: link with -z norelro for LLD or aarch64-elf

From: Nick Desaulniers <ndesaulniers@google.com>
To: Will Deacon <will@kernel.org>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	kernel-team <kernel-team@android.com>,
	"Peter Smith" <Peter.Smith@arm.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	stable <stable@vger.kernel.org>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Fāng-ruì Sòng" <maskray@google.com>,
	"Quentin Perret" <qperret@google.com>,
	"Alan Modra" <amodra@gmail.com>,
	"kernelci . org bot" <bot@kernelci.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: link with -z norelro for LLD or aarch64-elf
Date: Thu, 17 Dec 2020 13:07:41 -0800	[thread overview]
Message-ID: <CAKwvOd=LZHzR11kuhT2EjFnUdFwu5hQmxiwqeLB2sKC0hWFY=g@mail.gmail.com> (raw)
In-Reply-To: <20201217120118.GC17544@willie-the-truck>

On Thu, Dec 17, 2020 at 4:01 AM Will Deacon <will@kernel.org> wrote:
>
> On Wed, Dec 16, 2020 at 04:40:51PM -0800, Nick Desaulniers wrote:
> > With newer GNU binutils, linking with BFD produces warnings for vmlinux:
> > aarch64-linux-gnu-ld: warning: -z norelro ignored
> >
> Given that, prior to 3b92fa7485eb, we used to pass '-z norelro' if
> CONFIG_RELOCATABLE then was this already broken with the ELF toolchain?

Yes, though it would have been hard to foresee the change to BFD ~6
months later.

Specifically, binutils-gdb
commit 5fd104addfddb ("Emit a warning when -z relro is unsupported")
was committed Fri Jun 19 09:50:20 2020 +0930. The first git tag that
describes this commit was binutils-2_35 which was tagged Fri Jul 24
11:05:23 2020 +0100.

I noticed about a month ago that the version of
binutils-aarch64-linux-gnu installed on my gLinux workstation had auto
updated to version 2.35.1; I was authoring kernel patches for DWARF v5
support, which relied on 2.35 for DWARF v5 assembler support.  I
suspect Quentin's host was auto updated as well, at which point he
noticed and mentioned to me since I had touched `-z norelro` last.

But if we look at
commit 3bbd3db86470 ("arm64: relocatable: fix inconsistencies in
linker script and options")
which was committed at Tue Dec 4 12:48:25 2018 +0000, it was not
possible to foresee that binutils-gdb would change to produce such a
warning for such an emulation mode.

So I'm not sure whether my patch should either:
- have a fixes tag for just the latest commit that touched anything
related to `-z norelro`, mine, 3b92fa7485eb.
- have an additional fixes tag for 3bbd3db86470 which first introduced
`-z norelro`.
- have no fixes tag

I'll respin a v2 folding in Ard's suggestions.  Meanwhile, I've filed:
- https://bugs.llvm.org/show_bug.cgi?id=48549 against LLD
- https://sourceware.org/bugzilla/show_bug.cgi?id=27093 against BFD
-- 
Thanks,
~Nick Desaulniers