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Add: GDT, entry initializing for code and data segments

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xamidev
2024-07-14 10:22:42 +02:00
parent 2b05b8b74f
commit 007018790a
9 changed files with 80 additions and 2 deletions
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48
gdt.c Normal file
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@@ -0,0 +1,48 @@
#include "gdt.h"
struct gdt_entry
{
unsigned short limit_low;
unsigned short base_low;
unsigned char base_middle;
unsigned char access;
unsigned char granularity;
unsigned char base_high;
} __attribute__((packed));
struct gdt_ptr
{
unsigned short limit;
unsigned int base;
} __attribute__((packed));
struct gdt_entry gdt[3];
struct gdt_ptr gp;
extern void gdt_flush();
void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran)
{
gdt[num].base_low = (base & 0xFFFF);
gdt[num].base_middle = (base >> 16) & 0xFF;
gdt[num].base_high = (base >> 24) & 0xFF;
gdt[num].limit_low = (limit & 0xFFFF);
gdt[num].granularity = ((limit >> 16) & 0x0F);
gdt[num].granularity |= (gran & 0xF0);
gdt[num].access = access;
}
void gdt_install()
{
gp.limit = (sizeof(struct gdt_entry)*3) - 1;
gp.base = (unsigned int)&gdt;
gdt_set_gate(0, 0, 0, 0, 0);
gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
gdt_flush();
}