linux-kernel - Re: [PATCH 0/2] x86-64: allow using RIP-relative addressing for per-CPU data

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Date:	Tue, 04 Nov 2014 11:33:13 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Jan Beulich <JBeulich@...e.com>, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] x86-64: allow using RIP-relative addressing for per-CPU
 data

On 11/04/2014 12:49 AM, Jan Beulich wrote:
> Observing that per-CPU data (in the SMP case) is reachable by
> exploiting 64-bit address wraparound, these two patches
> arrange for using the one byte shorter RIP-relative addressing
> forms for the majority of per-CPU accesses.
> 
> 1: handle PC-relative relocations on per-CPU data
> 2: use RIP-relative addressing for most per-CPU accesses
> 
> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> 

I'm lost here.  Can you give an example of a physical and virtual
address of an instruction, the address within the gs segment, and why
the relocations are backwards?

--Andy
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