PING^2: [PATCH] i386: Add TARGET_INDIRECT_BRANCH_REGISTER

PING^2: [PATCH] i386: Add TARGET_INDIRECT_BRANCH_REGISTER

[H.J. Lu]

On Thu, Feb 8, 2018 at 10:05 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Sun, Jan 28, 2018 at 11:56 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Sat, Jan 27, 2018 at 2:12 PM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>>> For
>>>
>>> ---
>>> struct C {
>>>   virtual ~C();
>>>   virtual void f();
>>> };
>>>
>>> void
>>> f (C *p)
>>> {
>>>   p->f();
>>>   p->f();
>>> }
>>> ---
>>>
>>> -mindirect-branch=thunk-extern -O2 on x86-64 GNU/Linux generates:
>>>
>>> _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
>>>
>>> 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.  That region really has to be moved outside of
>>> the .cfi_startproc/.cfi_endproc bracket.
>>>
>>> This patch adds TARGET_INDIRECT_BRANCH_REGISTER to force indirect
>>> branch via register when -mindirect-branch=thunk-extern is used.  Now,
>>> -mindirect-branch=thunk-extern -O2 on x86-64 GNU/Linux generates:
>>>
>>> _Z1fP1C:
>>> .LFB0:
>>>         .cfi_startproc
>>>         pushq   %rbx
>>>         .cfi_def_cfa_offset 16
>>>         .cfi_offset 3, -16
>>>         movq    (%rdi), %rax
>>>         movq    %rdi, %rbx
>>>         movq    16(%rax), %rax
>>>         call    __x86_indirect_thunk_rax
>>>         movq    (%rbx), %rax
>>>         movq    %rbx, %rdi
>>>         popq    %rbx
>>>         .cfi_def_cfa_offset 8
>>>         movq    16(%rax), %rax
>>>         jmp     __x86_indirect_thunk_rax
>>>         .cfi_endproc
>>>
>>> Now "-mindirect-branch=thunk-extern" is equivalent to
>>> "-mindirect-branch=thunk-extern -mindirect-branch-register", which is
>>> used by Linux kernel.
>>>
>>> Tested on i686 and x86-64.  OK for trunk?
>>>
>>> Thanks.
>>>
>>> H.J.
>>> ----
>>> gcc/
>>>
>>>         PR target/84039
>>>         * config/i386/constraints.md (Bs): Replace
>>>         ix86_indirect_branch_register with
>>>         TARGET_INDIRECT_BRANCH_REGISTER.
>>>         (Bw): Likewise.
>>>         * config/i386/i386.md (indirect_jump): Likewise.
>>>         (tablejump): Likewise.
>>>         (*sibcall_memory): Likewise.
>>>         (*sibcall_value_memory): Likewise.
>>>         Peepholes of indirect call and jump via memory: Likewise.
>>>         * config/i386/i386.opt: Likewise.
>>>         * config/i386/predicates.md (indirect_branch_operand): Likewise.
>>>         (GOT_memory_operand): Likewise.
>>>         (call_insn_operand): Likewise.
>>>         (sibcall_insn_operand): Likewise.
>>>         (GOT32_symbol_operand): Likewise.
>>>         * config/i386/i386.h (TARGET_INDIRECT_BRANCH_REGISTER): New.
>>>
>>
>> Here is the updated patch  to disallow *sibcall_GOT_32 and *sibcall_value_GOT_32
>> for TARGET_INDIRECT_BRANCH_REGISTER.
>>
>> Tested on i686 and x86-64.  OK for trunk?
>>
>
> Hi Jan,
>
> https://gcc.gnu.org/ml/gcc-patches/2018-01/msg02233.html
>
> Is OK for trunk?
>

Hi Jan,

Can you take a look?  I have more retpoline patches which
depend on this one.

Thanks.


-- 
H.J.