linux-kernel - Re: x86 - clang / objtool status

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Date:   Wed, 24 Jul 2019 07:37:22 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        x86@...nel.org, Arnd Bergmann <arnd@...db.de>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: x86 - clang / objtool status

On Wed, Jul 24, 2019 at 09:47:32AM +0200, Peter Zijlstra wrote:
> On Tue, Jul 23, 2019 at 09:43:24PM -0500, Josh Poimboeuf wrote:
> > On Thu, Jul 18, 2019 at 10:40:09PM +0200, Thomas Gleixner wrote:
> > 
> > >   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x86: redundant UACCESS disable
> > 
> > Looking at this one, I think I agree with objtool.
> > 
> > PeterZ, Linus, I know y'all discussed this code a few months ago.
> > 
> > __copy_from_user() already does a CLAC in its error path.  So isn't the
> > user_access_end() redundant for the __copy_from_user() error path?
> 
> Hmm, is this a result of your c705cecc8431 ("objtool: Track original function across branches") ?
> 
> I'm thinking it might've 'overlooked' the CLAC in the error path before
> (because it didn't have a related function) and now it sees it and
> worries about it.

Yeah, I think so.

> Then again, I'm not seeing this warning on my GCC builds; so what's
> happening?

Good question...

-- 
Josh