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Date: Sun, 24 Sep 2006 22:25:57 -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: > That can't happen, since 0xc100000 is not in the kernel address space. > 0xc1000000 is though, perhaps that's what you meant? > Yes, it is. Though it doesn't actually make any material difference to my argument. >> So, in this case the %gs base will be loaded with 0xc100000-0xc0431100 = >> 0x4bccef00 >> > > > A negative offset, exactly, which can't happen, as I said. 0x4bccef00 is positive. The correct number is 0xc1000000-0xc0431100 = 0xbcef00 The %gs:per_cpu__foo addressing mode still calculates 0xbcef00+0xc0433800, which is still a subtraction. My essential point is that *all* kernel addresses (=kernel symbols) are negative, so using them as an offset from a segment base (any segment base) is a subtraction, which requires a 4G limit. J - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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