linux-kernel - Re: static_branch/jump

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Message-ID: <20210409213949.GA33256@worktop.programming.kicks-ass.net>
Date:   Fri, 9 Apr 2021 23:39:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Malcolm <dmalcolm@...hat.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-toolchains@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: Re: static_branch/jump_label vs branch merging

On Fri, Apr 09, 2021 at 05:07:15PM -0400, David Malcolm wrote:

> You've built a very specific thing out of asm-goto to fulfil the tough
> requirements you outlined above - as well as the nops, there's a thing
> in another section to contend with.
> 
> How to merge these asm-goto constructs?

By calling the function less, you emit less of them. Which then brings
us back to the whole pure/const thing.

> Doing so feels very special-case to the kernel and not something that
> other GCC users would find useful.

Doesn't it boil down to 'fixing' the pure/const vs asm-goto interaction?
I could imagine that having that interaction fixed could allow other
creative uses.