On Mon, Jan 22, 2018 at 4:21 AM, Florian Weimer <fwei...@redhat.com> wrote:
> I tried this:
>
> struct C {
> virtual ~C();
> virtual void f();
> };
>
> void
> f (C *p)
> {
> p->f();
> p->f();
> }
>
> with r256939 and -mindirect-branch=thunk -O2 on x86-64 GNU/Linux, and got
> this:
>
> _Z1fP1C:
> .LFB0:
> .cfi_startproc
> pushq %rbx
> .cfi_def_cfa_offset 16
> .cfi_offset 3, -16
> movq (%rdi), %rax
> movq %rdi, %rbx
> jmp .LIND1
> .LIND0:
> pushq 16(%rax)
> jmp __x86_indirect_thunk
> .LIND1:
> call .LIND0
> movq (%rbx), %rax
> movq %rbx, %rdi
> popq %rbx
> .cfi_def_cfa_offset 8
> movq 16(%rax), %rax
> jmp __x86_indirect_thunk_rax
> .cfi_endproc
>
> This doesn't look quite right. x86-64 is supposed to have asynchronous
> unwind tables by default, but there is nothing that reflects the change in
> the (relative) frame address after .LIND0. I think that region really has
> to be moved outside of the .cfi_startproc/.cfi_endproc bracket.
I'd like to remove __x86_indirect_thunk since it can't be made compatible
with CET:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83970
That means -mindirect-branch=thunk should imply -mindirect-branch-register.
When -fno-plt is used with __x86_indirect_thunk_reg, linker can convert call
via GOT to direct branch if function is locally defined:
https://groups.google.com/forum/#!topic/x86-64-abi/eED5lzn3_Mg
H.J.
