Initial commit: SUB-OS 64-Bit Production Monolithic Operating System with LazyBox userland suite

boot/gdt.asm

@@ -0,0 +1,43 @@
+; Global Descriptor Table Definition
+align 16
+gdt_start:
+    ; Null descriptor (0x00)
+    dq 0
+
+    ; 32-bit Code Segment (0x08)
+    dw 0xFFFF       ; Limit (low 16 bits)
+    dw 0x0000       ; Base (low 16 bits)
+    db 0x00         ; Base (next 8 bits)
+    db 10011010b    ; Access byte (Present, Ring 0, Code/Data, Executable, Read/Write)
+    db 11001111b    ; Flags (32-bit, 4KB granularity) and Limit (high 4 bits)
+    db 0x00         ; Base (high 8 bits)
+
+    ; 32-bit Data Segment (0x10)
+    dw 0xFFFF       ; Limit
+    dw 0x0000       ; Base
+    db 0x00         ; Base
+    db 10010010b    ; Access byte (Present, Ring 0, Code/Data, Read/Write)
+    db 11001111b    ; Flags and Limit
+    db 0x00         ; Base
+
+    ; 64-bit Code Segment (0x18)
+    dw 0x0000       ; Limit (ignored)
+    dw 0x0000       ; Base
+    db 0x00         ; Base
+    db 10011010b    ; Access byte (Present, Ring 0, Code/Data, Executable, Read/Write)
+    db 00100000b    ; Flags (64-bit code segment, Long Mode) and Limit
+    db 0x00         ; Base
+
+    ; 64-bit Data Segment (0x20)
+    dw 0x0000       ; Limit (ignored)
+    dw 0x0000       ; Base
+    db 0x00         ; Base
+    db 10010010b    ; Access byte (Present, Ring 0, Code/Data, Read/Write)
+    db 00000000b    ; Flags and Limit
+    db 0x00         ; Base
+
+gdt_end:
+
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1  ; Size of GDT minus 1
+    dd gdt_start                ; Base address of GDT