Re: RFC: (almost) getting rid of FIXUP/RESTORE_TOP_OF_STACK?

Andy Lutomirski
2015-02-25T16:09:46Z

On Tue, Feb 24, 2015 at 3:45 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
> On 02/24/2015 12:58 AM, Andy Lutomirski wrote:
>>> - Next possible change is to use PUSH insns to build the stack. Something along the lines of
>>> swapgs
>>> mov %rsp,%gs:old_rsp
>>> mov %gs:kernel_stack,%rsp
>>> sti
>>> push $__USER_DS /* pt_regs->ss */
>>> push %gs:old_rsp /* ->rsp */
>>> push %r11 /* ->rflags */
>>> push $__USER_CS /* ->cs */
>>> push %rcx /* ->rip */
>>> push %rax /* ->orig_rax */
>>> push %rdi
>>> push %rsi
>>> push %rdx
>>> push %rcx
>>> push $-ENOSYS /* ->rax */
>>> push %r8
>>> push %r9
>>> push %r10
>>> push %r11
>>> sub $(6*8),%rsp /* rbx, rbp, r12-r15 not saved */
>
> Correction:
> push %r11
> sub $(6*8),%rsp /* rbx, rbp, r12-r15 not saved */
> should be
> sub $(7*8),%rsp /* r11, rbx, rbp, r12-r15 not saved */
> since we don't need to save r11 either.
>
>>
>> Yay!
>
> "yay!" as in "I like this!" or as in "I am surprised" ?
>
>> Can we have a macro PUSH_XYZ for most of this?
>
> Yes, it can be a macro. I'm not sure we'll have more than one
> such place, tho.
> Do you want a macro even if it will be once-use only?
>

Maybe not. If it gets other uses, it can be macro-ized.

--
Andy Lutomirski
AMA Capital Management, LLC