linux-kernel - Re: [PATCH 13/13] x86_32: make percpu symbols zerobased on SMP

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Message-Id: <200901141048.59632.rusty@rustcorp.com.au>
Date:	Wed, 14 Jan 2009 10:48:58 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Tejun Heo <tj@...nel.org>
Cc:	ebiederm@...ssion.com, cl@...ux-foundation.org, mingo@...e.hu,
	travis@....com, linux-kernel@...r.kernel.org, hpa@...or.com,
	akpm@...ux-foundation.org, steiner@....com, hugh@...itas.com
Subject: Re: [PATCH 13/13] x86_32: make percpu symbols zerobased on SMP

On Tuesday 13 January 2009 21:08:17 Tejun Heo wrote:
> This patch makes percpu symbols zerobased on x86_32 SMP by using
> PERCPU_VADDR() with 0 vaddr in vmlinux_32.lds.S.  A new PHDR is added
> as existing ones cannot contain sections near address zero.
...
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Mike Travis <travis@....com>
> ---
>  arch/x86/kernel/cpu/common.c     |    8 ++++++++
>  arch/x86/kernel/head_32.S        |   37 ++++++++++++++++++++++++++++++++++---
>  arch/x86/kernel/setup_percpu.c   |    4 ----
>  arch/x86/kernel/vmlinux_32.lds.S |   16 +++++++++++++++-
>  4 files changed, 57 insertions(+), 8 deletions(-)

Hmm, the only reason for this change is to unify with 64-bit, yes?  Yet it
doesn't actually win us anything on that front, as this diffstat shows.

If gcc's -mcmodel=kernel had used a weak symbol for the offset of the stack
canary, we would have been happy.  Unfortunately generic per-cpu and x86-64
PDA were developed separately, so noone realize the problem until too late.

The basic series looks good: it will clash with my per-cpu work (mainly
because I remove the per_cpu__ prefix) in a purely-textual way though.

Thanks for this!
Rusty.
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