linux-kernel - Re: [PATCH v2 01/24] x86/xen: Mark cpu_bringup_and_idle() as dead_end

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Message-ID: <5e879610-6cee-00ac-9959-75f667c1967c@suse.com>
Date:   Mon, 30 Aug 2021 09:56:02 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, joro@...tes.org,
        boris.ostrovsky@...cle.com, x86@...nel.org, mbenes@...e.com,
        rostedt@...dmis.org, dvyukov@...gle.com, elver@...gle.com
Subject: Re: [PATCH v2 01/24] x86/xen: Mark cpu_bringup_and_idle() as
 dead_end_function

On 30.08.21 09:48, Peter Zijlstra wrote:
> On Mon, Aug 30, 2021 at 07:55:02AM +0200, Juergen Gross wrote:
>>>> From: Josh Poimboeuf <jpoimboe@...hat.com>
>>>> Subject: [PATCH] x86/xen: Move hypercall_page to top of the file
>>>>
>>>> Because hypercall_page is page-aligned, the assembler inexplicably adds
>>>> an unreachable jump from after the end of the previous code to the
>>>> beginning of hypercall_page.
>>>>
>>>> That confuses objtool, understandably.  It also creates significant text
>>>> fragmentation.  As a result, much of the object file is wasted text
>>>> (nops).
>>>>
>>>> Move hypercall_page to the beginning of the file to both prevent the
>>>> text fragmentation and avoid the dead jump instruction.
>>>>
>>>> $ size /tmp/head_64.before.o /tmp/head_64.after.o
>>>>      text       data        bss        dec        hex    filename
>>>>     10924     307252       4096     322272      4eae0
>>>> /tmp/head_64.before.o
>>>>      6823     307252       4096     318171      4dadb
>>>> /tmp/head_64.after.o
>>>>
>>>> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com
>>>
>>> Reviewed-by: Juergen Gross <jgross@...e.com>
>>
>> Umm, will this be carried through the tip tree, or shall I take it in
>> the xen tree?
> 
> I have it in the whole x86/objtool/paravirt series. I you want it in the
> Xen tree, I'll be happy to drop it from there, although I hope to get
> all that merged this cycles somewhere.
> 

Okay, I think it is better kept in your series then.


Juergen

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