Messages in this thread | | | Date | Wed, 20 Feb 2002 14:54:44 -0800 | From | Jason Yan <> | Subject | initialize page tables -- Re: paging question |
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Thank you Dick
Oops, I use a wrong subject, what I want to ask is how the pg0 be initialized
in head.S,
395 .org 0x2000 396 ENTRY(pg0)
so $pg0-__PAGE_OFFSET = 0x2000 - 0xC0000000 = 40002000, how comes bff00000 ?
>84 movl $pg0-_PAGE_OFFSET,%edi
%edi = bff00000 (or 40002000) ?
>87 2: stosl
that's move %eax to %es:%edi, __KERNEL_DS = 0x18, so %es is 0x18, according the gdt_table, 0x00cf92000000ffff, the base linear address is 0x00000000, that means %es:%edi = bff00000 (or 40002000), how can the %eax be moved into an nonexist ram, cause at that time, no page directory and and page table yet.
Anyway, thank you for your help.
Regards,
Jason
>> 48 cld >> 49 movl $(__KERNEL_DS),eax >> 50 movl eax,ds >> 51 movl eax,es >> 52 movl eax,fs >> 53 movl eax,gs >> 81 /* >> 82 * Initialize page tables >> 83 */ >> 84 movl $pg0-__PAGE_OFFSET,edi /* initialize page tables */ >> 85 movl $007,eax /* "007" doesn't mean with right to kill, but >> 86 PRESENT+RW+USER */ >> 87 2: stosl >> 88 add $0x1000,eax >> 89 cmp $empty_zero_page-__PAGE_OFFSET,edi >> 90 jne 2b >> >> I remove the SMP code. According the setup.S, gdt_table is setup as >> gdt_table: >> #.quad 0x0000000000000000; // null >> #.quad 0x0000000000000000; // not used >> #.quad 0x00cf9a000000ffff; // 0x10 kernel 4GB code at 0x00000000 >> #.quad 0x00cf92000000ffff; // 0x18 kernel 4GB data at 0x00000000 >> >> 1) So, what's in eax after line 49 ? 0x0 ? >> 2) Isn't __PAGE_OFFSET 0xC0000000 ? what's the result of $pg0-__PAGE_OFFSET ? >> >> Thanks, >> >> Jason >
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