linux-kernel - Re: [PATCH v2 10/11] x86/alternatives: Simplify ALTERNATIVE

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Message-ID: <20230915120553.GBZQRIoX+2s14BDaKw@fat_crate.local>
Date:   Fri, 15 Sep 2023 14:05:53 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        gregkh@...uxfoundation.org, nik.borisov@...e.com
Subject: Re: [PATCH v2 10/11] x86/alternatives: Simplify ALTERNATIVE_n()

On Fri, Sep 15, 2023 at 09:51:06AM +0200, Peter Zijlstra wrote:
> > So I see what you did with that @n argument, but urgh, do we really need
> > this? I mean, it just makes things harder to use and it doesn't actually
> > fix anything.. :/

It only addresses this repeating of the 661 labels:

# 53 "./arch/x86/include/asm/page_64.h" 1
	# ALT: oldnstr
661:
	# ALT: oldnstr
661:
	call clear_page_orig	#
662:

but this is only the produced asm which no one but me and you look at so
I guess it is not worth the effort.

I still think, though, that adding the comments explaining the situation
more is worth it because we will forget.

> That is, if we can magic this using __COUNTER__ without a user interface
> penalty, then sure. But the last time I tried that I failed utterly and
> ended up with labels like:
> 
>   .Lalt_old___COUNTER__:
> 
> no matter how many layers of CPP macro eval I stuck in it. So clearly I
> wasn't having a good day ....

Yeah, I tried it too because Matz said it should work with it but
I failed too. Reportedly, the approach should be to do that in CPP and
use CPP even for the asm macro but my CPP-fu is basic, to say the least.

I'll poke him next time we meet - I might've missed an aspect.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette