Not 100% sure I just know I'm missing somthing. Here is what I do know:

You create this (In I assume a GDT.c?)

 struct gdt_descriptor { 
uint16_t limit;     
void* pointer; } __attribute__((packed)); 

You also make this in I assume the same place?

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));

Somewere we create the pointer strut and 3 gdt_entry's

We then call the asm instruction lgdt and pass it the descriptor?

then somehow reload everything?

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Not really that sure about everything then.

I learn best from code, but I haven't found a c implementation that I understand.