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

Denys Vlasenko
2015-02-24T11:45:26Z

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?