linux-kernel - Re: [PATCH 2/12] i386: align data section to 4K boundary

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Date:	Wed, 4 Oct 2006 13:17:12 +0200
From:	Andi Kleen <ak@...e.de>
To:	vgoyal@...ibm.com
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Reloc Kernel List <fastboot@...ts.osdl.org>,
	ebiederm@...ssion.com, akpm@...l.org, horms@...ge.net.au,
	lace@...kratochvil.net, hpa@...or.com, magnus.damm@...il.com,
	lwang@...hat.com, dzickus@...hat.com, maneesh@...ibm.com
Subject: Re: [PATCH 2/12] i386: align data section to 4K boundary

On Tuesday 03 October 2006 19:06, Vivek Goyal wrote:
> 
> o Currently there is no specific alignment restriction in linker script
>   and in some cases it can be placed non 4K aligned addresses. This fails
>   kexec which checks that segment to be loaded is page aligned.
> 
> o I guess, it does not harm data segment to be 4K aligned.

iirc P4 optimization guide even recommends to keep writable data 
away one page from code to avoid some cache invalidations. But:

> diff -puN arch/i386/kernel/vmlinux.lds.S~i386-force-data-section-to-4K-aligned arch/i386/kernel/vmlinux.lds.S
> --- linux-2.6.18-git17/arch/i386/kernel/vmlinux.lds.S~i386-force-data-section-to-4K-aligned	2006-10-02 13:17:58.000000000 -0400
> +++ linux-2.6.18-git17-root/arch/i386/kernel/vmlinux.lds.S	2006-10-02 14:38:17.000000000 -0400
> @@ -52,6 +52,7 @@ SECTIONS
>    }
>  
>    /* writeable */
> +  . = ALIGN(4096);
>    .data : AT(ADDR(.data) - LOAD_OFFSET) {	/* Data */
>  	*(.data)
>  	CONSTRUCTORS

I would move the ".tracedata" section behind it first.

-Andi
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