linux-kernel - Re: [PATCH 08/46] static_call, lto: Mark static keys as _

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Date:   Thu, 17 Nov 2022 09:24:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Martin Liska <mliska@...e.cz>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 08/46] static_call, lto: Mark static keys as __visible

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@...stfloor.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.