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117 lines
2.7 KiB
C
117 lines
2.7 KiB
C
#ifndef _GDT_H
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#define _GDT_H
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#include <kernel.h>
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/*
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* Segment selector explanation (why kcode is 0x08?)
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*
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* Each segment selector must be 16 bits. These bits
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* have the following layout: (example is 0x08)
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* 0000000000001 0 00 (lsb)
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* | | '- Privilege level
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* | '--- Table indicator
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* '------ Index in table
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*
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* Bits 0-1 are the privilege level. x86 has four,
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* where 00 is the highest and 11 is the lowest. Only
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* these two are widely used. 00 being kernel space &
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* 11 being userspace. Bit 3 is the table indicator.
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* 0 means the GDT and 1 means the LDT. This will most
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* likely be 0. Bits 4-15 are the index. This is just
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* which descriptor in the table is used.
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*
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* SO, for the kernel code segment:
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* Privilege is 00 for kernel space, table indicator
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* s 0 for the GDT and the index is one, because it
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* is the second entry in our GDT (after null desc.)
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*/
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#define SEGMENT_SEL(_priv, _tab, _i)\
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(uint16_t)(((_i) << 3) | ((_tab) << 2) | (_priv))
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/*
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* Entries:
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* 0 Null desc.
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* 1 Kernel code desc.
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* 2 Kernel data desc.
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* 3 User code desc.
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* 4 User data desc.
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* 5 Task State Segment
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*/
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#define GDT_ENTRIES 6
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#define GDT_NULL SEGMENT_SEL(0, 0, 0)
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#define GDT_KERNEL_CODE SEGMENT_SEL(0, 0, 1)
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#define GDT_KERNEL_DATA SEGMENT_SEL(0, 0, 2)
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#define GDT_USER_CODE SEGMENT_SEL(3, 0, 3)
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#define GDT_USER_DATA SEGMENT_SEL(3, 0, 4)
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#define GDT_TSS SEGMENT_SEL(0, 0, 5)
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#define GDT_DESC(_lim, _base, _acc, _flag) (struct gdt_entry){\
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.limit = (_lim) & 0xffff,\
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.baseLow = (uint16_t)(_base),\
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.baseMid = (uint8_t)((_base) >> 16),\
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.access = (_acc),\
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.flags = (_flag << 4) | (((_lim) >> 16) & 0x0f),\
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.baseHigh = (uint8_t)((_base) >> 24),\
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}
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struct gdt_entry {
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uint16_t limit;
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uint16_t baseLow;
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uint8_t baseMid;
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uint8_t access;
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uint8_t flags; // low 4 bits are 4 msbs of limit, high 4 bits are flags
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uint8_t baseHigh;
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} __packed;
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struct gdt_pointer {
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uint16_t limit;
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uint32_t base;
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} __packed;
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struct tss_pointer {
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uint16_t link;
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uint16_t __reserved0;
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uint32_t esp0;
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uint16_t ss0;
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uint16_t __reserved1;
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uint32_t esp1;
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uint16_t ss1;
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uint16_t __reserved2;
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uint32_t esp2;
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uint16_t ss2;
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uint16_t __reserved3;
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uint32_t cr3;
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uint32_t eip;
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uint32_t eflags;
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uint32_t eax;
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uint32_t ecx;
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uint32_t edx;
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uint32_t ebx;
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uint32_t esp;
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uint32_t ebp;
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uint32_t esi;
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uint32_t edi;
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uint16_t es;
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uint16_t __reserved4;
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uint16_t cs;
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uint16_t __reserved5;
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uint16_t ss;
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uint16_t __reserved6;
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uint16_t ds;
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uint16_t __reserved7;
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uint16_t fs;
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uint16_t __reserved8;
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uint16_t gs;
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uint16_t __reserved9;
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uint16_t ldtr;
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uint32_t __reserved10;
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uint16_t iopb;
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uint32_t ssp;
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} __packed;
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void tss_esp0(uint32_t esp0);
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int gdt_init(void);
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#endif
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