Struct x86_64::structures::gdt::GlobalDescriptorTable

pub struct GlobalDescriptorTable { /* fields omitted */ }

A 64-bit mode global descriptor table (GDT).

In 64-bit mode, segmentation is not supported. The GDT is used nonetheless, for example for switching between user and kernel mode or for loading a TSS.

The GDT has a fixed size of 8 entries, trying to add more entries will panic.

You do not need to add a null segment descriptor yourself - this is already done internally.

Data segment registers in ring 0 can be loaded with the null segment selector. When running in ring 3, the ss register must point to a valid data segment which can be obtained through the Descriptor::user_data_segment() function. Code segments must be valid and non-null at all times and can be obtained through the Descriptor::kernel_code_segment() and Descriptor::user_code_segment() in rings 0 and 3 respectively.

For more info, see: x86 Instruction Reference for mov, Intel Manual, AMD Manual

Example

use x86_64::structures::gdt::{GlobalDescriptorTable, Descriptor};

let mut gdt = GlobalDescriptorTable::new();
gdt.add_entry(Descriptor::kernel_code_segment());
gdt.add_entry(Descriptor::user_code_segment());
gdt.add_entry(Descriptor::user_data_segment());

// Add entry for TSS, call gdt.load() then update segment registers

Methods

impl GlobalDescriptorTable

pub fn new() -> GlobalDescriptorTable

Creates an empty GDT.

pub fn add_entry(&mut self, entry: Descriptor) -> SegmentSelector

Adds the given segment descriptor to the GDT, returning the segment selector.

Panics if the GDT has no free entries left.

Trait Implementations

impl Debug for GlobalDescriptorTable

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Clone for GlobalDescriptorTable

fn clone(&self) -> GlobalDescriptorTable

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.