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

Josh Poimboeuf
2020-11-13T19:54:25Z

On Tue, Nov 10, 2020 at 10:59:55AM -0800, Sami Tolvanen wrote:
> On Tue, Nov 10, 2020 at 9:46 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > On Mon, Nov 09, 2020 at 08:29:24PM -0600, Josh Poimboeuf wrote:
> > > On Mon, Nov 09, 2020 at 03:11:41PM -0800, Sami Tolvanen wrote:
> > > > CONFIG_XEN
> > > >
> > > > __switch_to_asm()+0x0: undefined stack state
> > > > xen_hypercall_set_trap_table()+0x0: <=== (sym)
> >
> > With your branch + GCC 9 I can recreate all the warnings except this
> > one.
>
> In a gcc build this warning is replaced with a different one:
>
> vmlinux.o: warning: objtool: __startup_secondary_64()+0x7: return with
> modified stack frame
>
> This just seems to depend on which function is placed right after the
> code in xen-head.S. With gcc, the disassembly looks like this:
>
> 0000000000000000 <asm_cpu_bringup_and_idle>:
> 0: e8 00 00 00 00 callq 5 <asm_cpu_bringup_and_idle+0x5>
> 1: R_X86_64_PLT32 cpu_bringup_and_idle-0x4
> 5: e9 f6 0f 00 00 jmpq 1000
> <xen_hypercall_set_trap_table>
> ...
> 0000000000001000 <xen_hypercall_set_trap_table>:
> ...
> ...
> 0000000000002000 <__startup_secondary_64>:
>
> With Clang+LTO, we end up with __switch_to_asm here instead of
> __startup_secondary_64.

I still don't see this warning for some reason.

Is it fixed by adding cpu_bringup_and_idle() to global_noreturns[] in
tools/objtool/check.c?

--
Josh