linux-kernel - Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

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Message-ID: <20211109210736.GV174703@worktop.programming.kicks-ass.net>
Date:   Tue, 9 Nov 2021 22:07:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Bill Wendling <morbo@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        dvyukov@...gle.com, seanjc@...gle.com, pbonzini@...hat.com,
        mbenes@...e.cz, llvm@...ts.linux.dev,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

On Tue, Nov 09, 2021 at 11:22:44AM -0800, Nick Desaulniers wrote:

> I think the use of this feature (label-attributes) here isn't
> necessary though; because of the use of outputs, the "fallthrough"
> basic block needs to be placed immediately after the basic block
> terminated by the asm goto, at least in LLVM.  Was different ordering
> of basic blocks observed with GCC without this label attribute?

GCC does the same, but I wanted to have the exception stuff be in
.text.cold, but alas it doesn't do that. I left the attribute because of
it's descriptive value.

>  Unless the cold attribute is helping move
> ("shrink-wrap"?) the basic block to a whole other section
> (.text.cold.)?

I was hoping it would do that, but it doesn't on gcc-11.