Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 17 Nov 2022 09:24:11 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andi Kleen <andi@firstfloor.org>
Cc:     "Jiri Slaby (SUSE)" <jirislaby@kernel.org>,
        linux-kernel@vger.kernel.org, Josh Poimboeuf <jpoimboe@kernel.org>,
        Jason Baron <jbaron@akamai.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Martin Liska <mliska@suse.cz>, Jiri Slaby <jslaby@suse.cz>
Subject: Re: [PATCH 08/46] static_call, lto: Mark static keys as __visible
Message-ID: <Y3Xvq/TXwtLt4uon@hirez.programming.kicks-ass.net>
References: <20221114114344.18650-1-jirislaby@kernel.org>
 <20221114114344.18650-9-jirislaby@kernel.org>
 <Y3Jj67TZ9tA2a6Pf@hirez.programming.kicks-ass.net>
 <20221114203433.2pskttlyqjo3gua7@two.firstfloor.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20221114203433.2pskttlyqjo3gua7@two.firstfloor.org>
Precedence: bulk

On Mon, Nov 14, 2022 at 12:34:33PM -0800, Andi Kleen wrote:
> On Mon, Nov 14, 2022 at 04:51:07PM +0100, Peter Zijlstra wrote:
> > On Mon, Nov 14, 2022 at 12:43:06PM +0100, Jiri Slaby (SUSE) wrote:
> > > From: Andi Kleen <andi@firstfloor.org>
> > > 
> > > Symbols referenced from assembler (either directly or e.f. from
> > > DEFINE_STATIC_KEY()) need to be global and visible in gcc LTO because
> > > they could end up in a different object file than the assembler. This
> > > can lead to linker errors without this patch.
> > > 
> > > So mark static call functions as __visible, namely static keys here.
> > 
> > Why doesn't llvm-lto need this?
> 
> It has an integrated assembler that can feed this information to the LTO
> symbol table, while gas cannot do that.
> 
> There was some discussion to extend the gcc top level asm syntax to 
> express external symbols, but so far it doesn't exist.

Urgh, that's ugly too. Why does GCC insist on ugly solutions; clang has
shown it can be done sanely, follow.