linux-kernel - Re: [PATCH 18/46] entry, lto: Mark raw_irqentry_exit_cond_resched() as _

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Date:   Fri, 18 Nov 2022 16:50:46 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Martin Liska <mliska@...e.cz>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 18/46] entry, lto: Mark raw_irqentry_exit_cond_resched()
 as __visible

> Sure, they can play around with it but that does not require to merge
> all this nonsensical ballast for a half thought out compiler.

You are referring to __visible?

TBH I don't understand the problem. In general __visible is useful 
documentation,

so you know something is used from assembler or other strange contexts. 
Doing such things

explicitly marked instead of implicitly hidden and they just happen to 
work by accident

seems cleaner to me.

I can also see the __visible markings being useful for other purposes, 
e.g. static analysis tools or

dynamic instrumentation like the various sanitizers. Everything that is 
referenced outside

the normal code that the compiler sees may need some special handling.

That said I don't see the point of __visible_in_lto either, it should be 
just all __visible.

Similar argument applies to __noreorder, it's also useful documentation.

There are a few real workarounds in the patchkit that are a bit ugly, 
but __visible isn't it.

>
> If they want to do that they can apply the pile of patches as provided
> and play around.

It's very difficult to maintain out of tree, while in tree it's much 
simpler.

I think Linux should support its primary compiler well and not give up 
due to relatively small obstacles.

-Andi