linux-kernel - Re: [PATCH 2/5] percpu: Refactor percpu.h

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Date:	Thu, 5 Feb 2009 14:30:45 -0800
From:	Tony Luck <tony.luck@...el.com>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] percpu: Refactor percpu.h

On Sun, Jan 18, 2009 at 4:52 PM, Brian Gerst <brgerst@...il.com> wrote:
> Refactor the DEFINE_PER_CPU_* macros and add .data.percpu.first
> section.
>
> Signed-off-by: Brian Gerst <brgerst@...il.com>

> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 9f2a375..0e24202 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
...

> +#define DEFINE_PER_CPU_SECTION(type, name, section)                    \
> +       __attribute__((__section__(PER_CPU_BASE_SECTION section)))      \
>        PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name

Brian,

This causes errors for CONFIG_SMP=n builds on ia64.  If you look
at arch/ia64/include/asm/percpu.h you'll see that the !SMP case has


#define PER_CPU_ATTRIBUTES      __attribute__((__section__(".data.percpu")))

So we end up with section attributes of both ".data" and
".data.percpu" for every
DEFINE_PER_CPU used.  The compiler doesn't like that at all :-(


Perhaps PER_CPU_BASE_SECTION needs to be defined by <asm/percpu.h>
so ia64 can avoid the section conflict?

-Tony
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