linux-kernel - Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

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Message-ID: <4A4E609C.5030608@zytor.com>
Date:	Fri, 03 Jul 2009 12:48:44 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	lkml@...ethan.org
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

Michael S. Zick wrote:
> 
> Good point: (1<<(32-PAGE_SIFT)) would handle other than 4k pages.
> 
> I just hardcoded it as a working example of the change from setting
> the page table size by design rather than numeric error.
> 

As Jeremy pointed out, it's not wrong as written.  gas by design uses
arbitrary-precision arithmetic, and even if it didn't, it would still be
correct: (1 << 32) would collapse to 0, so all the rest of the
calculations would still be right.

Any way you can dump out this value from the vmlinux file (nm vmlinux |
grep MAPPING_BEYOND_END) in both cases?  What version of as/binutils do
you have installed?

> And yes, it has 512Mbyte of ram, so 1/2Mbyte page table sounds right to me.

/proc/cpuinfo, please?

	-hpa

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

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