103 lines
2.9 KiB
C
103 lines
2.9 KiB
C
#ifndef GDT_H
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#define GDT_H
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#include <stdint.h>
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extern char _end[], _edata[];
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#define KERNEL_CS 0x08 /* kernel code segment */
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#define KERNEL_DS 0x10 /* kernel data segment */
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#define USER_CS 0x18 /* user code segment */
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#define USER_DS 0x20 /* user data segment */
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#define TSS 0x28 /* TSS segment */
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#define KERNEL_BSS_SIZE ((int)_end - (int)_edata)
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#define NR_GDT_ENTRIES 6 /* entries in GDT descriptor */
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#define NR_IDT_ENTRIES 256 /* entries in IDT descriptor */
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/* low flags of Segment Descriptors */
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#define SD_CODE 0x0A /* CODE Exec/Read */
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#define SD_DATA 0x02 /* DATA Read/Write */
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#define SD_32INTRGATE 0x0E /* 32-bit Interrupt Gate (0D110) */
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#define SD_32TRAPGATE 0x0F /* 32-bit Trap Gate (0D111) */
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#define SD_CD 0x10 /* 0 = system / 1 = code/data */
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#define SD_DPL0 0x00 /* priority level 0 (kernel) */
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#define SD_DPL3 0x60 /* priority level 3 (user) */
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#define SD_PRESENT 0x80 /* segment present or valid */
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/* high flags Segment Descriptors */
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#define SD_OPSIZE32 0x04 /* 32-bit code and data segments */
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#define SD_PAGE4KB 0x08 /* page granularity (4KB) */
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/* low flags of the TSS Descriptors */
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#define SD_TSSPRESENT 0x89 /* TSS present and not busy flag */
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/* EFLAGS */
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#define EF_IOPL 12 /* IOPL bit */
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struct desc_r {
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uint16_t limit;
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uint32_t base_addr;
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} __attribute__((packed));
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struct seg_desc {
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unsigned sd_lolimit : 16; /* segment limit 0-15 bits */
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unsigned sd_lobase : 24; /* base address 0-23 bits */
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unsigned sd_loflags : 8; /* flags (P, DPL, S and TYPE) */
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unsigned sd_hilimit : 4; /* segment limit 16-19 bits */
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unsigned sd_hiflags : 4; /* flags (G, DB, 0 and AVL) */
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unsigned sd_hibase : 8; /* base address 24-31 bits */
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} __attribute__((packed));
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struct gate_desc {
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unsigned gd_looffset: 16; /* offset 0-15 bits */
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unsigned gd_selector: 16; /* segment selector */
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unsigned gd_flags : 16; /* flags (P, DPL, TYPE, 0 and NULL) */
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unsigned gd_hioffset: 16; /* offset 16-31 bits */
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} __attribute__((packed));
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struct tss_entry_struct {
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uint32_t prev_tss; // The previous TSS - with hardware task switching these form a kind of backward linked list.
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uint32_t esp0; // The stack pointer to load when changing to kernel mode.
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uint32_t ss0; // The stack segment to load when changing to kernel mode.
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// Everything below here is unused.
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uint32_t esp1; // esp and ss 1 and 2 would be used when switching to rings 1 or 2.
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uint32_t ss1;
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uint32_t esp2;
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uint32_t ss2;
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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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uint32_t es;
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uint32_t cs;
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uint32_t ss;
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uint32_t ds;
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uint32_t fs;
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uint32_t gs;
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uint32_t ldt;
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uint16_t trap;
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uint16_t iomap_base;
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} __attribute__((packed));
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extern struct tss_entry_struct tss;
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struct seg_desc gdt[NR_GDT_ENTRIES];
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struct desc_r gdtr = {
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sizeof(gdt) - 1,
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(uint32_t)&gdt
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};
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#endif
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