Message-ID: <20060929000301.GB11386@hmsreliant.homelinux.net>
Date:	Thu, 28 Sep 2006 20:03:01 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	linux-kernel@...r.kernel.org, mj@...ey.karlin.mff.cuni.cz,
	davej@...hat.com
Subject: Re: [PATCH] x86: update vmlinux.lds.S to place .data section on a page boundary

On Thu, Sep 28, 2006 at 07:22:06PM -0400, Neil Horman wrote:
> On Thu, Sep 28, 2006 at 10:42:20PM +0200, Sam Ravnborg wrote:
> > On Thu, Sep 28, 2006 at 04:12:49PM -0400, Neil Horman wrote:
> > > Patch to update vmlinux linker script so that .data section is on a page
> > > boundary.  without this change the kernel's .data section is on a non-4k
> > > boundary, and this prevents kexec from loading a new kernel.  Tested
> > > successfully by me.
> > NAK
> > 
> > > +  . = ALIGN(4096);
> > 
> > Do not use magic numbers like this.
> > Please replace 4096 with PAGE_SIZE - page.h is already included so it is
> > available.
> > This servers two purposes:
> > 1) This make it more self documenting
> > 2) It makes it more portable should we decide to do this in a general
> > way for all arch's.
> > 
> I'm happy to do this if that is the consensus, but if you look at the rest of
> the file, I'm simply following the standard that is currently in the file.  Are
> you sure you want me to go and revamp that through the entire script?
> 
> > And then maybe a comment why it is desireable to waste a lot of RAM
> > in some cases. For the embedded people wasting up to 4088 bytes
> > of RAM is not desireable.
> > 
> Again, its the standard of the script.  All other sections are page aligned (or
> rather were).  some recent changes have added a section data (a __tracedata
> section I think), which is 4 byte aligned, which shifted the subsequent section
> to be 4 byte aligned (the following note section as described in the PHDRS
> section is prefixed with a simmilar ALIGN macro to bring it back into page
> alignment.
> 
> Again, I'll repost with the adjustments you request, but first I'd like you please to
> look at the file and make sure thats best.  Currently, I'm more comfortable with
> the above, as it reflects the current standard of the script.
> 
> Regards
> Neil
> 
> > 
> > 	Sam
> 
Sorry, Replying to myself.  I forgot to mention in my last note why specifically
I was calling for this change, and why it was necessecary.  In addition to being
the standard in the script for executable sections, kexec also appears to rely
on PT_LOAD sections being on page boundaries.  With vmlinux.ld.s as it is, that
isn't the case, and so we can't load any kernels with kexec at the moment.  I've
seen this on the most recent fedora kernels (which have the latest version of
this linker script), and this patch corrects that.

Please look at the file in its entirety, and if you still feel that modifying
the script so all the ALIGN(4096) directives to be ALIGN(PAGE_SIZE) instead is
the direction to go, I'll implement the change and test it out.

Regards
Neil

> -- 
> /***************************************************
>  *Neil Horman
>  *Software Engineer
>  *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
>  ***************************************************/
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/***************************************************
 *Neil Horman
 *Software Engineer
 *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
 ***************************************************/
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