Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

Sami Tolvanen
2020-11-13T22:55:04Z

On Fri, Nov 13, 2020 at 2:34 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Fri, Nov 13, 2020 at 12:24:32PM -0800, Sami Tolvanen wrote:
> > > I still don't see this warning for some reason.
> >
> > Do you have CONFIG_XEN enabled? I can reproduce this on ToT master as follows:
> >
> > $ git rev-parse HEAD
> > 585e5b17b92dead8a3aca4e3c9876fbca5f7e0ba
> > $ make defconfig && \
> > ./scripts/config -e HYPERVISOR_GUEST -e PARAVIRT -e XEN && \
> > make olddefconfig && \
> > make -j110
> > ...
> > $ ./tools/objtool/objtool check -arfld vmlinux.o 2>&1 | grep secondary
> > vmlinux.o: warning: objtool: __startup_secondary_64()+0x2: return with
> > modified stack frame
> >
> > > Is it fixed by adding cpu_bringup_and_idle() to global_noreturns[] in
> > > tools/objtool/check.c?
> >
> > No, that didn't fix the warning. Here's what I tested:
>
> I think this fixes it:
>
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> Subject: [PATCH] x86/xen: Fix objtool vmlinux.o validation of xen hypercalls
>
> Objtool vmlinux.o validation is showing warnings like the following:
>
> # tools/objtool/objtool check -barfld vmlinux.o
> vmlinux.o: warning: objtool: __startup_secondary_64()+0x2: return with modified stack frame
> vmlinux.o: warning: objtool: xen_hypercall_set_trap_table()+0x0: <=== (sym)
>
> Objtool falls through all the empty hypercall text and gets confused
> when it encounters the first real function afterwards. The empty unwind
> hints in the hypercalls aren't working for some reason. Replace them
> with a more straightforward use of STACK_FRAME_NON_STANDARD.
>
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> arch/x86/xen/xen-head.S | 9 ++++-----
> include/linux/objtool.h | 8 ++++++++
> 2 files changed, 12 insertions(+), 5 deletions(-)

Confirmed, this fixes the warning, also in LTO builds. Thanks!

Tested-by: Sami Tolvanen <samitolvanen@google.com>

Sami