Rewritten GDT logic
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3a87b74224
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88c5196586
@ -50,3 +50,29 @@ _start:
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.include "./src/kernel/gdt/gdt.s"
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loadIDT:
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#load idt
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call init_idt
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sti
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# Try enable A20
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# mov $0x2401, %ax
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# int $0x15
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# enable protected mode
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mov %cr0, %eax
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or $1, %eax
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mov %eax, %cr0
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call kernel_main
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cli
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1: hlt
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jmp 1b
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.size _start, . - _start
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@ -1,75 +1,19 @@
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/* Tell processor to use our gdt*/
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gdt:
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.word (gdt_end - gdt_start -1) # Size of the GDT in bytes minus 1 for math reasons
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.int gdt_start # linear address of our GDT
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.global LoadGlobalDescriptorTable
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.att_syntax
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LoadGlobalDescriptorTable:
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lgdt gdtDescriptor
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.global load_gdt
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load_gdt:
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lgdt gdt
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# set the segment selecters
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movw $0x10, %ax
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movw $16, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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movw %ax, %ss
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ljmp $0x08, $flush
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flush:
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jmp $8,$flush
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flush:
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ret
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#load idt
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call init_idt
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sti
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# Try enable A20
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# mov $0x2401, %ax
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# int $0x15
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# enable protected mode
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mov %cr0, %eax
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or $1, %eax
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mov %eax, %cr0
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call kernel_main
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cli
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1: hlt
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jmp 1b
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.size _start, . - _start
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/*
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* Create the GDT
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*/
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.section .data
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gdt_start:
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gdt_null:
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.long 0x0
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.long 0x0
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gdt_kcode:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b10011010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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gdt_kdata:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b10010010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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gdt_end:
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@ -1,31 +1,61 @@
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#include "gdtc.h"
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#include "../tty/kterm.h"
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gdtEntry_t gdt[3];
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gdtSegmentPointer gdtPointer{};
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#define NULL_SEGMENT 0
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#define KERNEL_CODE_SEGMENT 1
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#define KERNEL_DATA_SEGMENT 2
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#define USER_CODE_SEGMENT 3
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#define USER_DATA_SEGMENT 4
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SegmentDescriptor GlobalDescriptorTable[5];
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GlobalDescriptorTableDescriptor gdtDescriptor;
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void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity ){
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GlobalDescriptorTable[which].base_low = (base & 0xFFFF );
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GlobalDescriptorTable[which].base_middle = (base >> 6) & 0xFF;
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GlobalDescriptorTable[which].base_high = (base >> 24) & 0xFF;
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GlobalDescriptorTable[which].limit_low = (limit & 0xFFFF);
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GlobalDescriptorTable[which].granularity = ((limit >> 16) & 0x0F);
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GlobalDescriptorTable[which].granularity |= (granularity & 0xF0);
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GlobalDescriptorTable[which].access = access;
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void gdtSetGate(int num, uint64_t base, uint64_t limit, uint8_t access,
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uint8_t gran){
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gdt[num].lBase = (base & 0xFFFF);
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gdt[num].mBase = (base >> 16) & 0xFF;
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gdt[num].hBase = (base >> 24) & 0xFF;
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gdt[num].lLimit = (limit & 0xFFFF);
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gdt[num].granularity = ((limit >> 16) & 0x0F);
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gdt[num].granularity |= (gran & 0xF0);
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gdt[num].access = access;
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}
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void setupGdt(){
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gdtPointer.limit = (sizeof(gdtEntry_t) * 3) - 1;
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gdtPointer.base = (uint32_t) &gdt;
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gdtSetGate(0, 0, 0, 0, 0);
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gdtSetGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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gdtSetGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
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printf("call to load gdt\n");
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load_gdt();
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void initGDT(){
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// NULL segment
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add_descriptor(NULL_SEGMENT, 0,0,0,0);
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// Kernel Code Segment
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add_descriptor(KERNEL_CODE_SEGMENT, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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// Kernel Data Segment
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add_descriptor(KERNEL_DATA_SEGMENT, 0, 0xFFFFFFFF, 0x92, 0xCF);
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// User Code Segment
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// TODO:
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// User Data Segement
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// TODO:
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// init Gdt Descriptor
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gdtDescriptor.limit = ((sizeof(SegmentDescriptor ) * 5 ) - 1);
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gdtDescriptor.base = (unsigned int) &GlobalDescriptorTable;
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LoadGlobalDescriptorTable();
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while (true)
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asm volatile("hlt");
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}
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@ -1,22 +1,27 @@
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#include <stdint.h>
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extern "C"{
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typedef struct {
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uint16_t lLimit;
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uint16_t lBase;
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uint8_t mBase;
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uint8_t access;
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uint8_t granularity;
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uint8_t hBase;
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} gdtEntry_t;
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struct gdtSegmentPointer {
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uint16_t limit;
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uint32_t base;
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};
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struct SegmentDescriptor {
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unsigned short limit_low;
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unsigned short base_low;
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unsigned char base_middle;
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unsigned char access;
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unsigned char granularity;
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unsigned char base_high;
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}__attribute__((packed));
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extern gdtSegmentPointer gdtPointer;
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extern void load_gdt();
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void setupGdt();
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}
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struct GlobalDescriptorTableDescriptor{
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unsigned short limit;
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unsigned int base;
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}__attribute__((packed));
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extern SegmentDescriptor GlobalDescriptorTable[];
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extern GlobalDescriptorTableDescriptor gdtDescriptor;
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void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity );
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extern "C" void LoadGlobalDescriptorTable();
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void initGDT();
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@ -26,8 +26,7 @@
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printf("kernel: 0x%x - 0x%x\n", &kernel_begin , &kernel_end);
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}
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printf("Call to setupGdt!\n");
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setupGdt();
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initGDT();
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}
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