linux-kernel - Re: [kernel-hardening] [PATCH v8 2/4] GCC plugin infrastructure

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Date:	Fri, 20 May 2016 20:10:32 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	pageexec@...email.hu, Emese Revfy <re.emese@...il.com>,
	kernel-hardening@...ts.openwall.com
Cc:	Andrew Donnellan <andrew.donnellan@....ibm.com>,
	linux-kbuild@...r.kernel.org, spender@...ecurity.net,
	mmarek@...e.com, keescook@...omium.org, linux@...musvillemoes.dk,
	fengguang.wu@...el.com, dvyukov@...gle.com,
	linux-kernel@...r.kernel.org, david.brown@...aro.org,
	yamada.masahiro@...ionext.com,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Daniel Axtens <dja@...ens.net>
Subject: Re: [kernel-hardening] [PATCH v8 2/4] GCC plugin infrastructure

On Thu, 2016-05-19 at 10:24 +0200, PaX Team wrote:
> On 19 May 2016 at 16:22, Michael Ellerman wrote:
> > On Wed, 2016-05-18 at 12:33 +0200, Emese Revfy wrote:
> > > Did you test the plugins with all gcc versions (4.5-6)?
> > 
> > What's the concern about gcc versions? Just not breaking the build on old
> > compilers?
> 
> the earlier plugin capable gcc versions used to install gcc headers in a somewhat
> ad-hoc manner resulting in compile time breakage for plugins and since some of
> those potentially missing headers are target specific, each target arch should
> be verified before enabling plugin support on them. things have much improved with
> gcc 5 (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61176) though there's still
> an occasional missing header but with wider use of plugins they will hopefully be
> discovered earlier now. 

OK thanks.

> perhaps linux-arch should be cc'ed on the plugin infrastructure
> so that arch maintainers are aware of this?

linux-arch is still fairly high traffic, so it's no guarantee arch maintainers
will see it, but it's probably worth a try.

> > I'm pretty sure powerpc big endian still builds with gcc 4.4.
> > 
> > However if Andrew's only tested on little endian, then that select should be
> > guarded with an "if CPU_LITTLE_ENDIAN". And to build LE you need gcc >= 4.9.
> 
> i guess that's part of the target tuple so in general arch maintainers should test
> the target tuples used on their arch with all the supported gcc versions (speaking
> of CC, not HOSTCC/HOSTCXX).

Yeah. I think we'll probably enable it gradually as folks get time to test it.
ie. ppc64le first, then ppc64 (BE), and then 32-bit if someone is interested.

cheers