From 30d6e8f850d2fe26fffdeef0c38fc627ef8bab9a Mon Sep 17 00:00:00 2001
From: "Anna (navi) Figueiredo Gomes" <navi@vlhl.dev>
Date: Wed, 13 Dec 2023 13:24:48 +0100
Subject: initial commit

currently with:
booted via multiboot 1
protected mode to long mode boostrap code
vga used for outputting
gdt and idt set up
identity paging for the whole memory reported by multiboot
pic and ps/2 set up
acpi code exists but is broken
---
 src/gdt.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 src/gdt.c

(limited to 'src/gdt.c')

diff --git a/src/gdt.c b/src/gdt.c
new file mode 100644
index 0000000..22489ac
--- /dev/null
+++ b/src/gdt.c
@@ -0,0 +1,44 @@
+#include <gdt.h>
+
+struct gdt_entry {
+	uint16_t limit_low;
+	uint16_t base_low;
+	uint8_t base_middle_low;
+	uint8_t access;
+	uint8_t gran;
+	uint8_t base_middle_high;
+	uint32_t base_high;
+	uint32_t reseved;
+} __attribute__((packed));
+
+struct gdt {
+	uint16_t limit;
+	uint64_t base;
+} __attribute__((packed));
+
+struct gdt_entry gdt[3];
+struct gdt gdt_ptr;
+
+extern void gdt_flush();
+
+void gdt_set_gate(size_t num, uint64_t base, uint32_t limit, uint8_t access, uint8_t gran) {
+	gdt[num] = (struct gdt_entry) {
+		.base_low = base & 0xFFFF,
+		.base_middle_low = (base >> 16) & 0xFF,
+		.base_middle_high = (base >> 24) & 0xFF,
+		.base_high = (base >> 32) & 0xFFFFFFFF,
+		.limit_low = limit & 0xFFFF,
+		.gran = ((limit >> 16) & 0x0F) | (gran & 0xF0),
+		.access = access
+	};
+}
+
+void gdt_install() {
+	gdt_ptr.limit = (sizeof(struct gdt_entry) * 3) - 1;
+	gdt_ptr.base = (uint64_t) &gdt;
+
+	gdt_set_gate(0, 0, 0, 0, 0);
+	gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+	gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+	gdt_flush();
+}
-- 
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