linux-kernel - Re: objtool warnings for kernel/trace/trace_selftest

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Message-ID: <20181217205535.GT25620@tassilo.jf.intel.com>
Date:   Mon, 17 Dec 2018 12:55:35 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: objtool warnings for kernel/trace/trace_selftest_dynamic.o

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