1 files changed, 108 insertions, 0 deletions
diff --git a/mirai.old/boot/gdt/gdt.zig b/mirai.old/boot/gdt/gdt.zig
new file mode 100644
index 0000000..7b24c3f
--- /dev/null
+++ b/mirai.old/boot/gdt/gdt.zig
@@ -0,0 +1,108 @@
+//! Global Descriptor Table
+
+const cpu = @import("../../asm/cpu.zig");
+const gdt_const = @import("../../common/constants/gdt.zig");
+const io = @import("../../asm/io.zig");
+const ports = @import("../../common/constants/ports.zig");
+const serial = @import("../../drivers/serial/serial.zig");
+const tss = @import("../tss/tss.zig");
+const types = @import("types.zig");
+
+pub const KERNEL_CODE = gdt_const.KERNEL_CODE;
+pub const KERNEL_DATA = gdt_const.KERNEL_DATA;
+pub const USER_DATA = gdt_const.USER_DATA;
+pub const USER_CODE = gdt_const.USER_CODE;
+pub const TSS_SEGMENT = gdt_const.TSS_SEGMENT;
+
+var gdt: [8]u64 align(16) = undefined;
+var gdt_ptr: types.Pointer = undefined;
+
+pub fn init() void {
+    gdt[0] = 0;
+    gdt[1] = create_code_descriptor(0, true);
+    gdt[2] = create_data_descriptor(0);
+    gdt[3] = create_data_descriptor(3);
+    gdt[4] = create_code_descriptor(3, true);
+
+    create_tss_descriptor(tss.get_address(), tss.get_size());
+
+    gdt_ptr = types.Pointer{
+        .limit = @sizeOf(@TypeOf(gdt)) - 1,
+        .base = @intFromPtr(&gdt),
+    };
+
+    cpu.load_global_descriptor_table(@intFromPtr(&gdt_ptr));
+    cpu.reload_segment_registers(KERNEL_DATA);
+    cpu.reload_code_segment(KERNEL_CODE);
+    cpu.load_task_register(TSS_SEGMENT);
+
+    io.out_byte(ports.PIC1_DATA, 0xFF);
+    io.out_byte(ports.PIC2_DATA, 0xFF);
+
+    serial.printf("GDT: code={x} data={x} ucode={x} udata={x} tss={x}\n", .{
+        KERNEL_CODE, KERNEL_DATA, USER_CODE, USER_DATA, TSS_SEGMENT,
+    });
+}
+
+fn create_code_descriptor(dpl: u8, long_mode: bool) u64 {
+    var desc: u64 = 0;
+
+    desc |= 0xFFFF;
+    desc |= (@as(u64, 0xF) << 48);
+
+    var access: u8 = 0;
+    access |= (1 << 0);
+    access |= (1 << 1);
+    access |= (1 << 3);
+    access |= (1 << 4);
+    access |= (@as(u8, dpl & 0x3) << 5);
+    access |= (1 << 7);
+    desc |= (@as(u64, access) << 40);
+
+    var flags: u8 = 0;
+    flags |= (1 << 3);
+    if (long_mode) {
+        flags |= (1 << 1);
+    } else {
+        flags |= (1 << 2);
+    }
+    desc |= (@as(u64, flags) << 52);
+
+    return desc;
+}
+
+fn create_data_descriptor(dpl: u8) u64 {
+    var desc: u64 = 0;
+
+    desc |= 0xFFFF;
+    desc |= (@as(u64, 0xF) << 48);
+
+    var access: u8 = 0;
+    access |= (1 << 0);
+    access |= (1 << 1);
+    access |= (1 << 4);
+    access |= (@as(u8, dpl & 0x3) << 5);
+    access |= (1 << 7);
+    desc |= (@as(u64, access) << 40);
+
+    var flags: u8 = 0;
+    flags |= (1 << 3);
+    flags |= (1 << 2);
+    desc |= (@as(u64, flags) << 52);
+
+    return desc;
+}
+
+fn create_tss_descriptor(base: u64, limit: u64) void {
+    var desc_low: u64 = 0;
+
+    desc_low |= (limit & 0xFFFF);
+    desc_low |= ((base & 0xFFFF) << 16);
+    desc_low |= ((base & 0xFF0000) >> 16) << 32;
+    desc_low |= (@as(u64, 0x89) << 40);
+    desc_low |= (((limit >> 16) & 0xF) << 48);
+    desc_low |= (((base & 0xFF000000) >> 24) << 56);
+
+    gdt[5] = desc_low;
+    gdt[6] = (base >> 32) & 0xFFFFFFFF;
+}