linux-kernel - Re: [PATCH] rcu: avoid checking for constant

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Message-ID: <20120112152912.GB2419@linux.vnet.ibm.com>
Date:	Thu, 12 Jan 2012 07:29:12 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Josh Triplett <josh@...htriplett.org>, laijs@...fujitsu.com,
	manfred@...orfullife.com, dhowells@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: avoid checking for constant

On Thu, Jan 12, 2012 at 11:57:10AM +0100, Jan Engelhardt wrote:
> On Thursday 2012-01-12 11:54, Eric Dumazet wrote:
> 
> >Le jeudi 12 janvier 2012 à 11:34 +0100, Jan Engelhardt a écrit :
> >
> >> When compiling kernel or module code with -O0, "offset" is no longer
> >> considered a constant, and therefore always triggers the build error
> >> that BUILD_BUG_ON is defined to yield.
> >
> >Why compiling kernel with -O0 is even considered ?
> 
> The compile error was observed when trying to compile an out-of-tree 
> module with -O0.

Hmmm...  Why not have a glue .c file in your out-of-tree module
that contains function like:

	void kfree_rcu_foo(struct foo *fp)
	{
		kfree_rcu(fp, foo_rcu);
	}

Compile this .c file normally, then apply -O0 only to the other
files in your module.

							Thanx, Paul

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