linux-kernel - Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

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Date:   Tue, 11 Oct 2016 07:20:49 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

On Tue, Oct 11, 2016 at 10:08:12AM +0200, Arnd Bergmann wrote:
> On Monday, October 10, 2016 3:23:22 PM CEST Josh Poimboeuf wrote:
> > 
> > Thanks for reporting it.  It looks like 'mtune=atom' sometimes makes a
> > slight change to one of the stack frame setup instructions.  Instead of:
> > 
> >   move rsp, rbp
> > 
> > It sometimes does:
> > 
> >   lea (%rsp),%rbp
> > 
> > They're two different instructions, but they have the same result.  It's
> > an easy fix for objtool.  I'll post a patch soon.
> > 
> > 
> 
> Ah, good to hear. I've replaced my patch with yours in my randconfig
> tests now and will let you know if there are any other warnings on
> atom. I've done a few thousand x86 randconfig builds now and done private
> patches for all warnings I got (I previously had fixes only for the arm
> warnings). I found objtool warnings for a few files in some configurations
> that do not involve -mtune=atom, maybe you can also look at what
> is going on there as I have no idea for how to address them:
> 
> drivers/scsi/fnic/fnic_main.o: warning: objtool: fnic_log_q_error() falls through to next function fnic_handle_link_event()
> drivers/scsi/snic/snic_res.o: warning: objtool: .text: unexpected end of section
> drivers/infiniband/sw/rxe/rxe_comp.o: warning: objtool: rxe_completer()+0x2f3: sibling call from callable instruction with changed frame pointer
> drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0x10f: sibling call from callable instruction with changed frame pointer
> kernel/locking/rwsem.o: warning: objtool: down_write_killable()+0x16: call without frame pointer save/setup
> 
> I can provide additional information for reproducing them if it's
> not immediately obvious what the problems are.

I'm really surprised the 0-day bot didn't find these.  I was under the
impression that it continuously did a bunch of randconfigs.

Anyway, if you could send the configs for the warnings, that would be
very helpful.

I also happen to be working on a significant rewrite of objtool and
these configs will come in handy for making a regression suite.

-- 
Josh