On Thu, Apr 06, 2023, Thomas Huth wrote:
> On 06/04/2023 01.01, Sean Christopherson wrote:
> > On Wed, 29 Mar 2023 14:38:14 +0200, Thomas Huth wrote:
> > > Recent versions of objcopy (e.g. from Fedora 37) complain:
> > >
> > > objcopy: x86/vmx.elf: warning: empty loadable segment detected at
> > > vaddr=0x400000, is this intentional?
> > >
> > > Seems like we can silence these warnings by properly specifying
> > > program headers in the linker script.
> > >
> > > [...]
> >
> > Applied to kvm-x86 next, thanks!
>
> Thanks for picking it up!
>
> > On the topic of annoying warnings, this one is also quite annoying:
> >
> > ld: warning: setjmp64.o: missing .note.GNU-stack section implies executable stack
> > ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
> >
> > I thought "-z noexecstack" would make it go away, but either I'm wrong or I'm not
> > getting the flag set in the right place.
>
> I never saw that warning here before, but I'm currently also still using an
> older version of GCC and binutils here since my development machine is still
> using RHEL 8 ...
>
> Anyway, does this happen for the normal builds, or for the efi builds?
Normal builds with gcc 12. I figured out what I got wrong, the "-z noexecstack"
needs to be passed to the linker, not the compiler/assembler. This does the trick,
I'll post an official patch later today:
diff --git a/x86/Makefile.common b/x86/Makefile.common
index 365e199f..c57d418a 100644
--- a/x86/Makefile.common
+++ b/x86/Makefile.common
@@ -62,7 +62,7 @@ else
# We want to keep intermediate file: %.elf and %.o
.PRECIOUS: %.elf %.o
-%.elf: LDFLAGS = -nostdlib $(arch_LDFLAGS)
+%.elf: LDFLAGS = -nostdlib $(arch_LDFLAGS) -z noexecstack
%.elf: %.o $(FLATLIBS) $(SRCDIR)/x86/flat.lds $(cstart.o)
$(LD) $(LDFLAGS) -T $(SRCDIR)/x86/flat.lds -o $@ \
$(filter %.o, $^) $(FLATLIBS)
> I can see a .note.GNU-stack entry in x86/efi/elf_x86_64_efi.lds ... maybe we
> need something similar in x86/flat.lds ?
I believe that just telling the linker that those sections don't need relocation
info. I suspect it's unnecessary copy+paste from UEFI sources.
The linker warning from setjmp64.o (and cstart64.o) is yelling about _not_ having
.note.GNU-stack, which is a magic section that tells the linker that the binary
doesn't need an executable stack. If I'm reading the NOTE correctly, it's saying
that the ability to have an executable stack is soon going away.
