From 3b134c245f6fc8aebe77ae3c252629e6a67b6c89 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 23 Dec 2025 01:50:31 -0500
Subject: mos/x86_64: Add GDT header

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 mos/sys/inc/arch/x86_64/gdt.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 mos/sys/inc/arch/x86_64/gdt.h

diff --git a/mos/sys/inc/arch/x86_64/gdt.h b/mos/sys/inc/arch/x86_64/gdt.h
new file mode 100644
index 0000000..35081b3
--- /dev/null
+++ b/mos/sys/inc/arch/x86_64/gdt.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2025, Ian Moffett.
+ * Provided under the BSD-3 clause.
+ */
+
+#ifndef _MACHINE_GDT_H_
+#define _MACHINE_GDT_H_ 1
+
+#ifndef __ASSEMBLER__
+#include <sdk/types.h>
+#include <sdk/defs.h>
+#endif  /* __ASSEMBLER__ */
+
+/* Kernel code/data */
+#define GDT_KCODE  0x08
+#define GDT_KDATA  0x10
+
+/* User code/data */
+#define GDT_UCODE  0x18
+#define GDT_UDATA  0x20
+
+/* Task state segment */
+#define GDT_TSS    0x28
+#define GDT_TSS_INDEX 0x05
+
+#ifndef __ASSEMBLER__
+typedef struct {
+    USHORT limit;
+    USHORT base_low;
+    UBYTE base_mid;
+    UBYTE access;
+    UBYTE granularity;
+    UBYTE base_hi;
+} PACKED GDT_ENTRY;
+
+typedef struct {
+    USHORT limit;
+    UPTR offset;
+} PACKED GDTR;
+
+#endif  /* !__ASSEMBLER__ */
+#endif  /* !_MACHINE_GDT_H_ */
-- 
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