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

Arvind Sankar
2020-07-14T20:35:42Z

On Tue, Jul 14, 2020 at 10:27:25PM +0200, Sedat Dilek wrote:
> On Tue, Jul 14, 2020 at 10:24 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > 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 -
>
> Not my day - today.
>
> $ git diff arch/x86/boot/compressed/Makefile
> diff --git a/arch/x86/boot/compressed/Makefile
> b/arch/x86/boot/compressed/Makefile
> index 789d5d14d8b0..9784ed37a5d7 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -51,8 +51,8 @@ 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 := -T
> +LDFLAGS_vmlinux += -pie $(call ld-option, --no-dynamic-linker)
>
> hostprogs := mkpiggy
> HOST_EXTRACFLAGS += -I$(srctree)/tools/include
>
> - Sedat -

Nope -- -T needs to be last, since it's (trickily) put together with the
first prerequisite $(obj)/vmlinux.lds.