linux-kernel - Re: [PATCH][v4] livepatch/ppc: Enable livepatching on powerpc

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Date:	Mon, 07 Mar 2016 14:29:56 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Petr Mladek <pmladek@...e.com>, linuxppc-dev@...abs.org,
	jeyu@...hat.com, jkosina@...e.cz, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, kamalesh@...ux.vnet.ibm.com, duwe@....de,
	live-patching@...r.kernel.org, Torsten Duwe <duwe@...e.de>
Subject: Re: [PATCH][v4] livepatch/ppc: Enable livepatching on powerpc

On Fri, 2016-03-04 at 10:31 +0100, Miroslav Benes wrote:
> On Fri, 4 Mar 2016, Michael Ellerman wrote:
> > On Thu, 2016-03-03 at 17:52 +0100, Petr Mladek wrote:
> > 
> > >     3. Added an error message when including
> > >        powerpc/include/asm/livepatch.h without HAVE_LIVEPATCH
> > 
> > I don't know why we want to do that, I don't see how it is helpful. It doesn't
> > even do what it says:
> > 
> > > +#ifdef CONFIG_LIVEPATCH
> > ...
> > > +#else /* CONFIG_LIVEPATCH */
> > > +#error Include linux/livepatch.h, not asm/livepatch.h
> > > +#endif /* CONFIG_LIVEPATCH */
> > 
> > If I turn on CONFIG_LIVEPATCH then I can quite happily include asm/livepatch.h
> > and not get an error. So the check doesn't do what the message suggests.
> 
> Well, yes. I looked into the archives to find if there was a reason to 
> even introduce it. It was not. It came up during a review process of the 
> livepatching patch set somehow and we left it there. I only changed the 
> error message to the mentioned one because we deemed it was better.

Thanks for looking into it.

> > And on x86 & s390 it does:
> > 
> >   #else
> >   #error Live patching support is disabled; check CONFIG_LIVEPATCH
> >   #endif
> 
> This is the old message. See 383bf44d1a8b ("livepatch: change the error 
> message in asm/livepatch.h header files").
> 
> Anyway, it really does not mean much. I'll send a patch for s390 and x86 
> to remove it completely in a minute.

Thanks. I know it's not a big deal, but the kernel is complicated enough
without extra code we don't really need :)

cheers