89 lines
3.6 KiB
C
89 lines
3.6 KiB
C
#include "console.h"
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#include "schedule.h"
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extern void setGdt(unsigned long long *, unsigned);
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// Each define here is for a specific flag in the descriptor.
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// Refer to the intel documentation for a description of what each one does.
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#define SEG_TYPE(x) ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data)
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#define SEG_PRES(x) ((x) << 0x07) // Present
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#define SEG_SAVL(x) ((x) << 0x0C) // Available for system use
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#define SEG_LONG(x) ((x) << 0x0D) // Long mode
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#define SEG_SIZE(x) ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32)
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#define SEG_GRAN(x) ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB)
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#define SEG_PRIV(x) (((x) & 0x03) << 0x05) // Set privilege level (0 - 3)
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#define SEG_DATA_RD 0x00 // Read-Only
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#define SEG_DATA_RDA 0x01 // Read-Only, accessed
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#define SEG_DATA_RDWR 0x02 // Read/Write
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#define SEG_DATA_RDWRA 0x03 // Read/Write, accessed
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#define SEG_DATA_RDEXPD 0x04 // Read-Only, expand-down
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#define SEG_DATA_RDEXPDA 0x05 // Read-Only, expand-down, accessed
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#define SEG_DATA_RDWREXPD 0x06 // Read/Write, expand-down
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#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed
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#define SEG_CODE_EX 0x08 // Execute-Only
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#define SEG_CODE_EXA 0x09 // Execute-Only, accessed
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#define SEG_CODE_EXRD 0x0A // Execute/Read
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#define SEG_CODE_EXRDA 0x0B // Execute/Read, accessed
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#define SEG_CODE_EXC 0x0C // Execute-Only, conforming
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#define SEG_CODE_EXCA 0x0D // Execute-Only, conforming, accessed
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#define SEG_CODE_EXRDC 0x0E // Execute/Read, conforming
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#define SEG_CODE_EXRDCA 0x0F // Execute/Read, conforming, accessed
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#define GDT_CODE_PL0 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(0) | SEG_CODE_EXRD
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#define GDT_DATA_PL0 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(0) | SEG_DATA_RDWR
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#define GDT_CODE_PL3 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(3) | SEG_CODE_EXRD
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#define GDT_DATA_PL3 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
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SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
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SEG_PRIV(3) | SEG_DATA_RDWR
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#define GDT_TSS SEG_GRAN(1) | SEG_PRES(1) | SEG_PRIV(0) | SEG_SIZE(1) | SEG_CODE_EXA
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unsigned long long gdt[6];
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unsigned long long
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create_descriptor(unsigned long base, unsigned long limit, unsigned short flag)
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{
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unsigned long long descriptor;
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// Create the high 32 bit segment
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descriptor = limit & 0x000F0000;
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descriptor |= (flag << 8) & 0x00F0FF00;
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descriptor |= (base >> 16) & 0x000000FF;
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descriptor |= base & 0xFF000000;
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// Shift by 32 to allow for low part of segment
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descriptor <<= 32;
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// Create the low 32 bit segment
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descriptor |= base << 16;
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descriptor |= limit & 0x0000FFFF;
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return descriptor;
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}
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void init_tss(struct tss_t *tss) {
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gdt[5] = create_descriptor((unsigned long)tss, sizeof(struct tss_t), (GDT_TSS));
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asm __volatile__ ( "ltr %%ax" : : "a" ( 0x28 ) );
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}
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void init_gdt(void)
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{
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gdt[0] = create_descriptor(0, 0, 0); // Null descriptor
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gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0)); // kernel code segment
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gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0)); // kernel data segment
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gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3)); // user code segment
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gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3)); // user data segment
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setGdt(gdt, 48);
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}
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