Collaboration diagram for Global Descriptor Table:

Data Structures
struct	gdtr
	The GDT is pointed to by the value in the GDTR register. More...

struct	gdt_descriptor
	A single entry inside the GDT. More...

struct	tss
	Segment. More...

union	segment_selector
	Identifies a segment inside the GDT or LDT. More...

Enumerations
enum	{ }
	Known fixed indexes inside the GDT. More...

Functions
void	gdt_init (void)
	Initialize the GDTR and GDT. More...

void	gdt_load_segment (gdt_descriptor, u16 index)
	Load a segment descriptor into the Global Descriptor Table. More...

void	gdt_log (void)
	Print the content of the GDT and GDTR.

void	gdt_set_esp0 (u32)
	Modify the kernel stack pointer inside the current TSS.

Detailed Description

Global Descriptor Table

The GDT is responsible for segmenting the physical address space into different parts with different level of security each.

The segments can contain either code or data.

Each "segment" can then be accessed using a selector. These selectors are the ones stored inside the segement registers (cs, ds ..) When addressing a linear address (~physical), the processor infact dereferences an offset inside the related segment's address range.

Warning: This is a x86 structure only

See also: https://wiki.osdev.org/Global_Descriptor_Table

Enumeration Type Documentation

◆ anonymous enum

anonymous enum

Enumerator
GDT_ENTRY_KERNEL_CODE	Required NULL segment.
GDT_ENTRY_KERNEL_DATA	Kernel code segment.
GDT_ENTRY_USER_CODE	Kernel data segment.
GDT_ENTRY_USER_DATA	User code segment.
GDT_ENTRY_TSS	User data segment.

Function Documentation

◆ gdt_init()

void gdt_init ( void )

Load the GDT's base address int GDTR
Setup the NULL segment at offset 0
Add our global segment descriptors (ring 0)

◆ gdt_load_segment()

void gdt_load_segment	(	gdt_descriptor	segment,
		u16	index
	)

Parameters

segment	The segment's content
index	The segment's index within the GDT.

Data Structures

Enumerations