linux-kernel - Re: [PATCH 1/5] all: s390: move wrapper infrastructure to generic headers

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Date:	Tue, 2 Feb 2016 20:54:34 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Yury Norov <ynorov@...iumnetworks.com>
Cc:	linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
	arnd@...db.de, pinskia@...il.com, Prasun.Kapoor@...iumnetworks.com,
	catalin.marinas@....com, Nathan_Lynch@...tor.com,
	linux-kernel@...r.kernel.org, agraf@...e.de,
	klimov.linux@...il.com, broonie@...nel.org,
	joseph@...esourcery.com, schwidefsky@...ibm.com,
	linux-arm-kernel@...ts.infradead.org,
	christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH 1/5] all: s390: move wrapper infrastructure to generic
 headers

Hi Yury,

On Tue, Feb 02, 2016 at 05:08:26PM +0100, Heiko Carstens wrote:
> See e.g. 485d52768685 ("sys_personality: change sys_personality() to accept
> "unsigned int" instead of u_long") would have been a candidate which could
> silently break architectures which need compat wrappers.

Ok, this example is of course wrong. But now I can claim that also somebody
who should know better makes these mistakes.. :)

> > I don't know much about s390 specifics. Maybe because of that I do not
> > understand completely your worries. I'm OK with both 1st and 2nd
> > version, but I'd choose 2nd one because it allows inlines, and we
> > don't need the compat_wrapper.c.
> 
> It would be only nicer if we can guarentee correctness all the time. That
> being said I'm about to revert my own commit :)
> 
> So if you want to go without compat_wrapper.c then we should have a
> solution which will do the right thing all the time without that a system
> call author has to know about the sign and zero extension issue some
> architectures face. It _will_ go wrong.

So I think I can summarize my point to: if you can enforce correctness, why
shouldn't you do it if the performance impact is only a single instruction.

However I'll try to write an addon patch to your patch series. Maybe we can
still get rid of compat_wrapper.c in a way which makes both of us happy.
Also.. the idea with the alias names for compat wrappers does seem to have
the disadvantage that it will pollute /proc/kallsyms for example.

Anyway, I'm not sure if I will be able to come up with something this week
though.