Messages in this thread |  | | | Date | Thu, 19 Feb 2004 16:33:11 +0800 | | From | Coywolf Qi Hunt <> | | Subject | { Linux not only practical, but an ideal. } Re: [PATCH 2.4.24] Fix GDT limit in setup.S |
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Coywolf Qi Hunt wrote:
> Richard B. Johnson wrote: > >> On Tue, 17 Feb 2004, Coywolf Qi Hunt wrote: >> >> >>> Hello 2.4.xx hackers, >>> >>> In setup.S, i feel like that the gdt limit 0x8000 is not proper and it >>> should be 0x800. How came 0x800 into 0x8000 in 2.4.xx code? Is there a >>> story? It shouldn't be a careless typo. 256 gdt entries should be >>> enough and since it's boot gdt, 256 is ok even if the code is run on SMP >>> with 64 cpus. >>> >> >> >> The first element has nothing to do with the number of GDT entries. >> It represents the LIMIT. Because the granularity bit is >> set meaning 4 kilobyte pages and 0x8000 * 0x1000 = 0x8000000 >> | | >> | |_______ Page size >> |______________ GDT value >> This is the size of address space that is unity-mapped for boot. >> >> The granularity is also not the number of GDT entries. It >> represents the length for which the GDT definition applies. >> >> Because this GDT is used only for booting, somebody decided that >> there would never be any boot code beyond 2 GB so there was no >> reason to make room for it. If you change the number to 0x0800, >> you are declaring that neither the boot code nor any RAM-disk >> combination will ever exceed 0x800 * 0x1000 = 0x800000 bytes. >> Therefore you broke my imbedded system. Do not do this. >> >> >>> At least the comment doesn't match the code. Either fix the code or fix >>> the comment. We really needn't so many GDT entries. Let's use the intel >>> segmentation in a most limited way. Below follows a patch fixing the >>> code. >>> >>> I don't have the latest 2.4.24, but setup.S isn't changed from 2.4.23 to >>> 2.4.24. >>> >>> Regards, Coywolf >>> > > Thank you for you kindly reply, though I really don not agree with you. > But thanks very much, since you are the only one replying me. I CCed to > all the 2.0 2.2 2.4 maintainers. > >
Hello Richard B. Johnson,
I've just find out where the problem lying in your answer, that you are not talking the same thing as i am. You are talking about the descriptor on which you are quite correct, while I am talking about GDTR, similar to selector, but not selector, could be called `selector' in GDTR. Two different things.
To All Hackers,
plz take my patch to make our kernel more perfect. Linux should be not only practical, but an ideal. And i have more such patches to send.
Regards, Coywolf
-- Coywolf Qi Hunt Admin of http://GreatCN.org and http://LoveCN.org
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