Re: [PATCH V3 4/7] x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Mar 15, 2022 at 03:39:46PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> 
> Moving PUSH_AND_CLEAR_REGS out of error_entry doesn't change any
> functionality.
> 
> It makes error_entry() do not fiddle with the stack.
> 
> It will enlarge the size:
> 
> size arch/x86/entry/entry_64.o.before:
>    text	   data	    bss	    dec	    hex	filename
>   17916	    384	      0	  18300	   477c	arch/x86/entry/entry_64.o
> 
> size --format=SysV arch/x86/entry/entry_64.o.before:
> .entry.text                      5528      0
> .orc_unwind                      6456      0
> .orc_unwind_ip                   4304      0
> 
> size arch/x86/entry/entry_64.o.after:
>    text	   data	    bss	    dec	    hex	filename
>   26868	    384	      0	  27252	   6a74	arch/x86/entry/entry_64.o
> 
> size --format=SysV arch/x86/entry/entry_64.o.after:
> .entry.text                      8200      0
> .orc_unwind                     10224      0
> .orc_unwind_ip                   6816      0
> 
> But .entry.text in x86_64 is 2M aligned, enlarging it to 8.2k doesn't
> enlarge the final text size.

So I don't much care about the orc data, that's only used when
unwinding, a relatively rare occasion, anyway. But the text increase
does bother me a little, this can blow up I$ misses on syscall heavy
workloads.