linux-kernel - Re: [PATCH V2 3/7] x86/entry: move PUSH_AND_CLEAR_REGS out of error

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Date:   Thu, 3 Mar 2022 09:54:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH V2 3/7] x86/entry: move PUSH_AND_CLEAR_REGS out of
 error_entry

On Thu, Mar 03, 2022 at 11:54:30AM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> Moving PUSH_AND_CLEAR_REGS out of error_entry doesn't change any
> functionality.  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.
> 
> The tables .orc_unwind[_ip] are enlarged due to it adds many pushes.
> 
> It is prepared for not calling error_entry() from XENPV in later patch
> and for future converting the whole error_entry into C code.

And also, IIUC, folding that int80 thing a few patches down, right?