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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 25 Feb 2015 08:09:21 -0800
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Subject: Re: RFC: (almost) getting rid of FIXUP/RESTORE_TOP_OF_STACK?
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Alexander van Heukelum <heukelum@fastmail.fm>
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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
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