sandpile.org -- x86 architecture -- descriptor tables

x86 architecture
descriptor tables

protected mode IDT, GDT, and LDT

offset	IDT
+0000h	gate #00h descriptor
+0008h	gate #01h descriptor
...	...
	e.g. task gate
	e.g. interrupt gate
	e.g. trap gate
	...
+07F8h	gate #FFh descriptor
+0800h	unused
...
+FFFFh

offset	GDT	LDT
+0000h	NULL descriptor	descriptor
+0008h	descriptor	descriptor
...	...	...
	e.g. code segment desc.	e.g. code segment desc.
	e.g. data segment desc.	e.g. data segment desc.
	e.g. call gate desc.	e.g. call gate desc.
	e.g. task gate desc.	e.g. task gate desc.
	e.g. LDT segment desc.	...
	e.g. TSS segment desc.
	...
+FFF8h	descriptor	descriptor

protected mode IDT64, GDT, and LDT

offset	IDT64
+0000h	gate #00h descriptor
+0010h	gate #01h descriptor
...	...
	e.g. 64-bit interrupt gate
	e.g. 64-bit trap gate
	...
+0FF8h	gate #FFh descriptor
+1000h	unused
...
+FFFFh
note	transitions through IDT64 gates clear the lowest 4 bits of RSP before the return stack frame gets pushed

offset	GDT	LDT
+0000h	NULL descriptor	descriptor
+0008h	descriptor	descriptor
...	...	...
	e.g. code segment desc.	e.g. code segment desc.
	e.g. data segment desc.	e.g. data segment desc.
	e.g. 64-bit call gate desc.	e.g. 64-bit call gate desc.
	e.g. 64-bit LDT desc.	...
	e.g. 64-bit TSS desc.
	...
+FFF8h	descriptor	descriptor

real mode IVT

offset	IVT
+0000h	vector #00h	offset
+0002h	vector #00h	segment
+0004h	vector #01h	offset
+0006h	vector #01h	segment
...	vector #xxh	offset
...	vector #xxh	segment
+03FCh	vector #FFh	offset
+03FEh	vector #FFh	segment
+0400h	unused
...
+FFFFh