Re: objtool warnings for kernel/trace/trace_selftest_dynamic.o

From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Miroslav Benes <mbenes@suse.cz>
Subject: Re: objtool warnings for kernel/trace/trace_selftest_dynamic.o
Date: Mon, 17 Dec 2018 12:55:35 -0800	[thread overview]
Message-ID: <20181217205535.GT25620@tassilo.jf.intel.com> (raw)
In-Reply-To: <20181217192938.GF2218@hirez.programming.kicks-ass.net>

On Mon, Dec 17, 2018 at 08:29:38PM +0100, Peter Zijlstra wrote:
> On Mon, Dec 17, 2018 at 12:16:38PM -0600, Josh Poimboeuf wrote:
> 
> > > Yes LTO causes the to be treated like static functions.
> > > 
> > > I guess noclone is unlikely to be really needed here because these
> > > functions are unlikely to be cloned.
> > > 
> > > So as a workaround it could be removed.
> > > 
> > > But note we have other noclone functions in the tree (like in KVM)
> > > which actually need it.
> > 
> > How about we just use the __used attribute then?  It seems to have the
> > same result of preventing IPA optimizations (without the weird side
> > effect of missing frame pointers).
> 
> AFAIK we don't have any in-tree LTO, so it can all go in the bin.

I have patches for 4.20, and I was actually thinking about resending
soon. It will need a few changes, but not too bad.

FWIW there's also a user base who used the out of tree patches
for some time.

> 
> When/if we get the LTO trainwreck sorted -- which very much includes
> getting that memory-order-consume fixed -- we can revisit all that.

What do you mean? I'm not aware of any LTO problems with memory-order-consume?

-Andi