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

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Date:   Mon, 17 Dec 2018 20:22:06 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: objtool warnings for kernel/trace/trace_selftest_dynamic.o

> The plugin is only used for older versions of GCC.  Newer versions have
> the same functionality builtin with -fsanitize-coverage=trace-pc.

Ok and the frame pointer issue is with the older version only?

> 
> So the problem is GCC.  We're using a function attribute which at least
> oneGCC developer doesn't recommend.  If you want to keep the LTO support
> then '__used' seems like a much better choice.

I guess __used will work for now.

Still would be better to root cause it properly, but I guess that's
ok for now. The lack of understanding may eventually come back
to bite you later.

FWIW i did some tests and I don't see noclone affecting frame pointer
with gcc 8. The only thing I saw was that empty functions ended up
without frame pointer.

I suspect you'll need to fix up the other users of noclone too.

-Andi