Re: [PATCH v2 1/3] vmlinux.lds.h: Add .gnu.version* to DISCARDS

[Fangrui Song]

On 2020-06-22, Kees Cook wrote:
> On Mon, Jun 22, 2020 at 03:00:43PM -0700, Fangrui Song wrote:
> > On 2020-06-22, Kees Cook wrote:
> > > For vmlinux linking, no architecture uses the .gnu.version* section,
> > > so remove it via the common DISCARDS macro in preparation for adding
> > > --orphan-handling=warn more widely.
> > >
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > ---
> > > include/asm-generic/vmlinux.lds.h | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > > index db600ef218d7..6fbe9ed10cdb 100644
> > > --- a/include/asm-generic/vmlinux.lds.h
> > > +++ b/include/asm-generic/vmlinux.lds.h
> > > @@ -934,6 +934,7 @@
> > > 	*(.discard)							\
> > > 	*(.discard.*)							\
> > > 	*(.modinfo)							\
> > > +	*(.gnu.version*)						\
> > > 	}
> > >
> > > /**
> > > --
> > > 2.25.1
> >
> > I wonder what lead to .gnu.version{,_d,_r} sections in the kernel.
>
> This looks like a bug in bfd.ld? There are no versioned symbols in any
> of the input files (and no output section either!)
>
> The link command is:
> $ ld -m elf_x86_64 --no-ld-generated-unwind-info -z noreloc-overflow -pie \
> --no-dynamic-linker   --orphan-handling=warn -T \
> arch/x86/boot/compressed/vmlinux.lds \
> arch/x86/boot/compressed/kernel_info.o \
> arch/x86/boot/compressed/head_64.o arch/x86/boot/compressed/misc.o \
> arch/x86/boot/compressed/string.o arch/x86/boot/compressed/cmdline.o \
> arch/x86/boot/compressed/error.o arch/x86/boot/compressed/piggy.o \
> arch/x86/boot/compressed/cpuflags.o \
> arch/x86/boot/compressed/early_serial_console.o \
> arch/x86/boot/compressed/kaslr.o arch/x86/boot/compressed/kaslr_64.o \
> arch/x86/boot/compressed/mem_encrypt.o \
> arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/acpi.o \
> -o arch/x86/boot/compressed/vmlinux
>
> None of the inputs have the section:
>
> $ for i in arch/x86/boot/compressed/kernel_info.o \
> arch/x86/boot/compressed/head_64.o arch/x86/boot/compressed/misc.o \
> arch/x86/boot/compressed/string.o arch/x86/boot/compressed/cmdline.o \
> arch/x86/boot/compressed/error.o arch/x86/boot/compressed/piggy.o \
> arch/x86/boot/compressed/cpuflags.o \
> arch/x86/boot/compressed/early_serial_console.o \
> arch/x86/boot/compressed/kaslr.o arch/x86/boot/compressed/kaslr_64.o \
> arch/x86/boot/compressed/mem_encrypt.o \
> arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/acpi.o \
> ; do echo -n $i": "; readelf -Vs $i | grep 'version'; done
> arch/x86/boot/compressed/kernel_info.o: No version information found in this file.
> arch/x86/boot/compressed/head_64.o: No version information found in this file.
> arch/x86/boot/compressed/misc.o: No version information found in this file.
> arch/x86/boot/compressed/string.o: No version information found in this file.
> arch/x86/boot/compressed/cmdline.o: No version information found in this file.
> arch/x86/boot/compressed/error.o: No version information found in this file.
> arch/x86/boot/compressed/piggy.o: No version information found in this file.
> arch/x86/boot/compressed/cpuflags.o: No version information found in this file.
> arch/x86/boot/compressed/early_serial_console.o: No version information found in this file.
> arch/x86/boot/compressed/kaslr.o: No version information found in this file.
> arch/x86/boot/compressed/kaslr_64.o: No version information found in this file.
> arch/x86/boot/compressed/mem_encrypt.o: No version information found in this file.
> arch/x86/boot/compressed/pgtable_64.o: No version information found in this file.
> arch/x86/boot/compressed/acpi.o: No version information found in this file.
>
> And it's not in the output:
>
> $ readelf -Vs arch/x86/boot/compressed/vmlinux | grep version
> No version information found in this file.
>
> So... for the kernel we need to silence it right now.

Re-link with -M (or -Map file) to check where .gnu.version{,_d,_r} input
sections come from?

If it is a bug, we should probably figure out which version of binutils
has fixed the bug.