linux-kernel - Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel

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Message-ID: <45177664.3060103@goop.org>
Date:	Sun, 24 Sep 2006 23:25:40 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Andi Kleen <ak@....de>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.osdl.org>
Subject: Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel

Rusty Russell wrote:
> I don't think so.  There's *never* address subtraction, there's
> sometimes 32 bit wrap (glibc uses this to effect subtraction, sure).
> But there's no wrap here.
>   
Hm, I guess, so long as you assume the kernel data segment is always 
below the kernel heap.

> To test, I changed the following:
>
> --- smpboot.c.~8~	2006-09-25 15:51:50.000000000 +1000
> +++ smpboot.c	2006-09-25 16:00:36.000000000 +1000
> @@ -926,8 +926,9 @@
>  					      unsigned long per_cpu_off)
>  {
>  	unsigned limit, flags;
> +	extern char __per_cpu_end[];
>  
> -	limit = (1 << 20);
> +	limit = PAGE_ALIGN((long)__per_cpu_end) >> PAGE_SHIFT;
>   
limit is a size, rather than the end address, so this isn't quite right.

    J
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