From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Gerecke <killertofu@gmail.com>,
linux-kernel@vger.kernel.org,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>,
Jason Gerecke <jason.gerecke@wacom.com>,
Ard Biesheuvel <ardb@kernel.org>,
"x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
Date: Fri, 12 Feb 2021 16:27:42 +0100 [thread overview]
Message-ID: <YCaebvpeLjY5oRAs@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210212094059.5f8d05e8@gandalf.local.home>
On Fri, Feb 12, 2021 at 09:40:59AM -0500, Steven Rostedt wrote:
> On Thu, 11 Feb 2021 13:48:48 -0800
> Jason Gerecke <killertofu@gmail.com> wrote:
>
> > When compiling an external kernel module with `-O0` or `-O1`, the following
> > compile error may be reported:
> >
> > ./arch/x86/include/asm/jump_label.h:25:2: error: impossible constraint in ‘asm’
> > 25 | asm_volatile_goto("1:"
> > | ^~~~~~~~~~~~~~~~~
> >
> > It appears that these lower optimization levels prevent GCC from detecting
> > that the key/branch arguments can be treated as constants and used as
> > immediate operands. To work around this, explicitly add the `const` label.
>
> Yes this makes sense. The "i" constraint needs to be a constant.
Right, using -O[01] seems a little daft though. But yeah, that patch is
correct and won't cause harm.
I've queued it for after the next merge window.
next prev parent reply other threads:[~2021-02-12 15:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 21:48 Jason Gerecke
2021-02-12 14:40 ` Steven Rostedt
2021-02-12 15:27 ` Peter Zijlstra [this message]
2021-02-12 15:55 ` Jason Gerecke
2021-02-12 16:14 ` Josh Poimboeuf
2021-03-03 8:15 ` [tip: locking/core] " tip-bot2 for Jason Gerecke
2021-03-06 11:54 ` tip-bot2 for Jason Gerecke
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