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 22:08:04 +0200	[thread overview]
Message-ID: <CA+icZUXBggJtwtWmyXEwgu1WztrcTiLrZCW1_QqSw2SiThOkfQ@mail.gmail.com> (raw)
In-Reply-To: <CA+icZUXoZzhUMRsVVexazd=oFK4vKa1KJN5=_KXz+fcYxcA4Rw@mail.gmail.com>

On Tue, Jul 14, 2020 at 9:53 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, Jul 14, 2020 at 9:29 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > On Tue, Jul 14, 2020 at 08:30:14PM +0200, Sedat Dilek wrote:
> > > > I did a full new build...
> > > >
> > > > ...and it fails with ld.lld-11 as linker:
> > > >
> > > > ld.lld-11 -m elf_x86_64 -pie  --no-dynamic-linker -r -o
> > > > arch/x86/boot/compressed/.tmp_misc.o arch/x86/boot/compressed/misc.o
> > > > -T arch/x86/boot/compressed/.tmp_misc.ver; mv -f
> > > > arch/x86/boot/compressed/.tmp_misc.o arch/x86/boot/compressed/misc.o;
> > > > rm -f arch/x86/boot/compressed/.tmp_misc.ver; fi
> > > > *** ld.lld-11: error: -r and -pie may not be used together ***
> > > > make[5]: *** [scripts/Makefile.build:281:
> > > > arch/x86/boot/compressed/misc.o] Error 1
> > > >
> > > > It's annoying to fail on the last minutes of a build.
> > > > Sorry for being very honest.
> > > >
> > >
> > > I applied this diff...
> > >
> > > $ git diff arch/x86/boot/compressed/Makefile
> > > diff --git a/arch/x86/boot/compressed/Makefile
> > > b/arch/x86/boot/compressed/Makefile
> > > index 789d5d14d8b0..9ba52a656838 100644
> > > --- a/arch/x86/boot/compressed/Makefile
> > > +++ b/arch/x86/boot/compressed/Makefile
> > > @@ -51,7 +51,10 @@ 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.
> > > +# LLD linker does not allow -r and -pie options to be used together.
> > > +ifndef CONFIG_LD_IS_LLD
> > >  KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
> > > +endif
> > >  LDFLAGS_vmlinux := -T
> > >
> > >  hostprogs      := mkpiggy
> > >
> > > ...and was able to build, assemble, link arch/x86/boot/compressed/*.
> > >
> > > - Sedat -
> >
> > Thanks for the test.
> >
> > Can you share your .config? The error messages look like they're coming
> > from running modversions on misc.o, which is unexpected as it shouldn't
> > have any exported symbols, and it doesn't in my builds.
> >
> > 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?

I cannot test as I modified my local Git and re-invoking my
build-script is doing a whole new build-dance.

- Sedat -