linux-kernel - Re: linux-next: build failure after merge of the rcu tree

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Message-ID: <20160108150850.1ec97e78@canb.auug.org.au>
Date:	Fri, 8 Jan 2016 15:08:50 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Boqun Feng <boqun.feng@...il.com>, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: linux-next: build failure after merge of the rcu tree

Hi Paul,

On Thu, 7 Jan 2016 19:41:57 -0800 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
>
> Indeed, I suspect that SRCU might not be the only thing that would like
> static per-CPU variables.  ;-)

from include/linux/percpu-defs.h:

 * s390 and alpha modules require percpu variables to be defined as
 * weak to force the compiler to generate GOT based external
 * references for them.  This is necessary because percpu sections
 * will be located outside of the usually addressable area.
 *
 * This definition puts the following two extra restrictions when
 * defining percpu variables.
 *
 * 1. The symbol must be globally unique, even the static ones.
 * 2. Static percpu variables cannot be defined inside a function.
 *
 * Archs which need weak percpu definitions should define
 * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
 *
 * To ensure that the generic code observes the above two
 * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
 * definition is used for all cases.

so they can be static, but must be globally unique.
-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au