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

    > Will do some digging on the others...

    Thanks!

    Sami

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