linux-kernel - Re: [PATCH 1/3] x86: record relocation offset

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Message-ID: <4B3BADDA.8040102@zytor.com>
Date:	Wed, 30 Dec 2009 11:45:30 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	fche LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] x86: record relocation offset

On 12/30/2009 05:15 AM, Arnaldo Carvalho de Melo wrote:
> 
> I'm no expert on the intricacies of boot_params, but all the other hunks
> seems sensible, but can't we provide a non-perf specific way of getting
> the relocate_offset? I guess other tools would also love to have it.
> 
> What about systemtap, don't they solve this in some other way? Frank?
> 

I at one point proposed that boot_params should be exported in toto via
sysfs.  This got rather brutally shut down as "it's just a debugging
feature" and got moved to debugfs (/debug/boot_params/data).  However,
the entire boot_params structure is available there.

Regardless of the reporting method, the patch passing this in by
modifying the early assembly code, though, is more than a little
pointless.  The kernel already knows where it is loaded -- obviously, by
sheer necessity -- and knows how it was itself configured, and as such
we can do this calculation in C code without modifying boot_params or
the early bootstrap.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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