separating: there will be libk and libc

kernel/gdt.c

@@ -0,0 +1,44 @@
+// Global descriptor table setup
+// Author: xamidev
+// Licensed under the Unlicense. See the repo below.
+// https://github.com/xamidev/blankos
+
+#include "gdt.h"
+#include "../libk/stdio.h"
+
+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);
+	
+	// Ring 0 code + data
+	gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+	gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+
+	// Ring 3
+	//gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
+	//gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
+
+	gdt_flush();
+	printf("[kernel] GDT gates set (ring 0), gdt=0x%x\n", (unsigned int)&gdt);
+}