README.md

os

Usage

Requirements

• mkisofs - install cdrkit on arch linux
• nasm

Global Descriptor Table (GDT)

Bits	Name	Description
1	Present	Set to 1 for used segments
2	Privelage	00 is highest privelage down to 11
1	Type	1 if segment is code or data segment
4	Type Flags	See below
4	Other Flags	See below

Type Flags

Flag Position	Name	Description
1xxx	Executable/Code	Whether this is a code segment
x1xx	Conforming or Direction	See below
xx1x	Readable or Writable	See below
xxx1	Accessed	Set by the CPU when the segment is being used

If the executable flag was set then, the second and third flags are:

Flag Position	Name	Description
x1xx	Conforming	Whether this code can be executed from lower privelage segments
xx1x	Readable	Whether this segment is readable

Otherwise, for data segments, the middle two flags are instead:

Flag Position	Name	Description
x1xx	Direction	Whether this code can be executed from lower privelage segments
xx1x	Writeable	Whether this segment is writeable

Other Flags

Flag Position	Name	Description
1xxx	Granularity	When set, limit *= 0x1000
x1xx	32 Bit	Whether this segment will use 32 bit memory
xx1x	64 Bit	Whether this segment will use 64 bit memory
xxx1	AVL