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To: Rusty Russell <rusty@rustcorp.com.au>
Cc: davidm@hpl.hp.com, linux-kernel@vger.kernel.org, torvalds@transmeta.com,
        rth@twiddle.net
Subject: Re: [PATCH] 2.5.1-pre5: per-cpu areas
In-Reply-To: <15504.7958.677592.908691@napali.hpl.hp.com.suse.lists.linux.kernel> <E16lMzi-0002bb-00@wagner.rustcorp.com.au.suse.lists.linux.kernel>
From: Andi Kleen <ak@suse.de>
Date: 14 Mar 2002 09:39:57 +0100
In-Reply-To: Rusty Russell's message of "14 Mar 2002 05:37:11 +0100"
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Rusty Russell <rusty@rustcorp.com.au> writes:

> In message <15504.7958.677592.908691@napali.hpl.hp.com> you write:
> > OK, I see this.  Unfortunately, HIDE_RELOC() causes me problems
> > because it prevents me from taking the address of a per-CPU variable.
> > This is useful when you have a per-CPU structure (e.g., cpu_info).
> > Perhaps there should/could be a version of HIDE_RELOC() that doesn't
> > dereference the resulting address?
> 
> Yep, valid point.  Patch below: please play.

Please don't do that. I cannot easily take the address of a per CPU 
variable on x86-64, or rather only with additional overhead. If you need the
address of one please use a different macro for that.

[on x86-64 per cpu data is referenced using a segment register, but
leaq %segreg:offset,%reg does not do the expected thing, it just loads 
offset but doesn't add in the segment register base address. To get the
address I always need to fetch a pointer from the the per cpu data 
that points to itself and work with that]

-Andi
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