linux-kernel - Re: [PATCH] Kconfig: Explicitly disable asm goto w/ outputs on gcc-11 (and earlier)

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Date: Fri, 9 Feb 2024 11:01:24 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Sean Christopherson <seanjc@...gle.com>, "Andrew Pinski (QUIC)" <quic_apinski@...cinc.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Masahiro Yamada <masahiroy@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] Kconfig: Explicitly disable asm goto w/ outputs on gcc-11
 (and earlier)

On Fri, 9 Feb 2024 at 10:55, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> And also pessimizes all asm gotos (for gcc) including ones that don't
> contain output as described in 43c249ea0b1e.  The version checks would
> at least not pessimize those.

Yeah, no, we should limit that workaround only to the asm goto with
outputs case.

We should also probably get rid of the existing "asm_volatile_goto()"
macro name entirely. That name was always pretty horrific, in that it
didn't even mark the asm as volatile even in the case where it did
anything.

So the name of that macro made little sense, and the new workaround
should be only for asm goto with outputs. So I'd suggest jmaking a new
macro with that name:

   #define asm_goto_output(x...)

and on gcc use that old workaround, and on clang just make it be a
plain "asm goto".

Hmm?

            Linus