Re: [PATCH v4 0/7] x86/boot: Remove runtime relocations from compressed kernel

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
	Fangrui Song <maskray@google.com>,
	Dmitry Golovin <dima@golovin.in>,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Daniel Kiper <daniel.kiper@oracle.com>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>, "H . J . Lu" <hjl@sourceware.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 0/7] x86/boot: Remove runtime relocations from compressed kernel
Date: Tue, 14 Jul 2020 22:24:07 +0200	[thread overview]
Message-ID: <CA+icZUVcyAfXqyAQp+bjb0bx5z2Q0Bfyt899AxJASXY-GCRCrA@mail.gmail.com> (raw)
In-Reply-To: <20200714202100.GB902932@rani.riverdale.lan>

On Tue, Jul 14, 2020 at 10:21 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, Jul 14, 2020 at 10:08:04PM +0200, Sedat Dilek wrote:
> > > >
> > > > In any case, I think the right fix here would be to add -pie and
> > > > --no-dynamic-linker to LDFLAGS_vmlinux instead of KBUILD_LDFLAGS.
> > >
> > > Hmm, you might be right with moving to LDFLAGS_vmlinux.
> > >
> >
> > We will need the "ifndef CONFIG_LD_IS_LLD" as -r and -pie cannot be
> > used together.
> > Is that the or not the fact when moving to LDFLAGS_vmlinux?
>
> LDFLAGS_vmlinux will only be used to link boot/compressed/vmlinux,
> whereas KBUILD_LDFLAGS is used for all linker invocations, and in
> particular the little link to do the modversions stuff ends up using it.
>
> So once we move -pie --no-dynamic-linker to the more correct
> LDFLAGS_vmlinux and/or stop modversions running, we'll be fine. Being
> able to use -pie with lld is one of the goals of this series.
>

OK, I am doing a new full kernel build with:

$ git diff arch/x86/boot/compressed/Makefile

diff --git a/arch/x86/boot/compressed/Makefile
b/arch/x86/boot/compressed/Makefile
index 789d5d14d8b0..056a738e47c6 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -51,7 +51,7 @@ UBSAN_SANITIZE :=n
 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
-KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
+LDFLAGS_vmlinux += -pie $(call ld-option, --no-dynamic-linker)
 LDFLAGS_vmlinux := -T

 hostprogs      := mkpiggy

- Sedat -
