Messages in this thread | | | Date | Sun, 24 Sep 2006 22:25:57 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel |
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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.
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