First steps reading multiboot info. Added GDT.

1 files changed, 28 insertions, 0 deletions

diff --git a/kernel/gdt.c b/kernel/gdt.c
new file mode 100644
index 0000000..7d23289
--- /dev/null
+++ b/kernel/gdt.c
@@ -0,0 +1,28 @@
+#include "gdt.h"
+
+gdt_entry gdt[] = {
+	gdt_entry_init(0, 0, 0),
+	gdt_entry_init(0, 0xfffff, 0xc09a), // Code segment.
+	gdt_entry_init(0, 0xfffff, 0xc092), // Data segment.
+	gdt_entry_init(0, 0xfffff, 0xc0fa), // User mode code segment.
+	gdt_entry_init(0, 0xfffff, 0xc0f2), // User mode data segment.
+};
+
+gdt_ptr gdtr = {
+	.base = gdt,
+	.limit = sizeof(gdt) - 1
+};
+
+void gdt_init() {
+	asm volatile(
+		"lgdt (%0)\n"
+		"mov %w1, %%ds\n"
+		"mov %w1, %%es\n"
+		"mov %w1, %%fs\n"
+		"mov %w1, %%gs\n"
+		"mov %w1, %%ss\n"
+		"ljmp $0x08, $.flush\n"
+		".flush:\n"
+		: : "r" (&gdtr), "r" (0x10)
+	);
+}