Rewritten GDT logic

This commit is contained in:
2021-11-16 21:17:49 +01:00
parent 3a87b74224
commit 88c5196586
5 changed files with 111 additions and 107 deletions

View File

@ -1,31 +1,61 @@
#include "gdtc.h"
#include "../tty/kterm.h"
gdtEntry_t gdt[3];
gdtSegmentPointer gdtPointer{};
#define NULL_SEGMENT 0
#define KERNEL_CODE_SEGMENT 1
#define KERNEL_DATA_SEGMENT 2
#define USER_CODE_SEGMENT 3
#define USER_DATA_SEGMENT 4
SegmentDescriptor GlobalDescriptorTable[5];
GlobalDescriptorTableDescriptor gdtDescriptor;
void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity ){
GlobalDescriptorTable[which].base_low = (base & 0xFFFF );
GlobalDescriptorTable[which].base_middle = (base >> 6) & 0xFF;
GlobalDescriptorTable[which].base_high = (base >> 24) & 0xFF;
GlobalDescriptorTable[which].limit_low = (limit & 0xFFFF);
GlobalDescriptorTable[which].granularity = ((limit >> 16) & 0x0F);
GlobalDescriptorTable[which].granularity |= (granularity & 0xF0);
GlobalDescriptorTable[which].access = access;
void gdtSetGate(int num, uint64_t base, uint64_t limit, uint8_t access,
uint8_t gran){
gdt[num].lBase = (base & 0xFFFF);
gdt[num].mBase = (base >> 16) & 0xFF;
gdt[num].hBase = (base >> 24) & 0xFF;
gdt[num].lLimit = (limit & 0xFFFF);
gdt[num].granularity = ((limit >> 16) & 0x0F);
gdt[num].granularity |= (gran & 0xF0);
gdt[num].access = access;
}
void setupGdt(){
gdtPointer.limit = (sizeof(gdtEntry_t) * 3) - 1;
gdtPointer.base = (uint32_t) &gdt;
gdtSetGate(0, 0, 0, 0, 0);
gdtSetGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
gdtSetGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
printf("call to load gdt\n");
load_gdt();
void initGDT(){
// NULL segment
add_descriptor(NULL_SEGMENT, 0,0,0,0);
// Kernel Code Segment
add_descriptor(KERNEL_CODE_SEGMENT, 0, 0xFFFFFFFF, 0x9A, 0xCF);
// Kernel Data Segment
add_descriptor(KERNEL_DATA_SEGMENT, 0, 0xFFFFFFFF, 0x92, 0xCF);
// User Code Segment
// TODO:
// User Data Segement
// TODO:
// init Gdt Descriptor
gdtDescriptor.limit = ((sizeof(SegmentDescriptor ) * 5 ) - 1);
gdtDescriptor.base = (unsigned int) &GlobalDescriptorTable;
LoadGlobalDescriptorTable();
while (true)
asm volatile("hlt");
}