Struct TaskStateSegment

#[repr(C, packed(1))]
pub struct TaskStateSegment {
    pub reserved: u32,
    pub rsp: [u64; 3],
    pub reserved2: u64,
    pub ist: [u64; 7],
    pub reserved3: u64,
    pub reserved4: u16,
    pub iomap_base: u16,
}

Although hardware task-switching is not supported in 64-bit mode, a 64-bit task state segment (TSS) must exist.

The TSS holds information important to 64-bit mode and that is not directly related to the task-switch mechanism. This information includes:

RSPn

The full 64-bit canonical forms of the stack pointers (RSP) for privilege levels 0-2. RSPx is loaded in whenever an interrupt causes the CPU to change RPL to x. Note on a syscall entry this field is not used to load a stack, setting the stack there is the handler’s responsibility (however when using the int instruction in user-space, we load the stack from RSPn).

ISTn

The full 64-bit canonical forms of the interrupt stack table (IST) pointers. You can set an interrupt vector to use an IST entry in the Interrupt Descriptor Table by giving it a number from 0 - 7. If 0 is selected, then the IST mechanism is not used. If any other number is selected then when that interrupt vector is called the CPU will load RSP from the corresponding IST entry. This is useful for handling things like double faults, since you don’t have to worry about switching stacks; the CPU will do it for you.

I/O map base address

The 16-bit offset to the I/O permission bit map from the 64-bit TSS base.

The operating system must create at least one 64-bit TSS after activating IA-32e mode. It must execute the LTR instruction (in 64-bit mode) to load the TR register with a pointer to the 64-bit TSS responsible for both 64-bitmode programs and compatibility-mode programs (load_tr).

Fields

reserved: u32

rsp: [u64; 3]

The full 64-bit canonical forms of the stack pointers (RSP) for privilege levels 0-2.

reserved2: u64

ist: [u64; 7]

The full 64-bit canonical forms of the interrupt stack table (IST) pointers.

reserved3: u64

reserved4: u16

iomap_base: u16

The 16-bit offset to the I/O permission bit map from the 64-bit TSS base.

Implementations

impl TaskStateSegment

pub const fn new() -> TaskStateSegment

Creates a new empty TSS.

pub fn set_rsp(&mut self, pl: Ring, stack_ptr: u64)

Sets the stack pointer (stack_ptr) to be used for when an interrupt causes the CPU to change RPL to pl.

pub fn set_ist(&mut self, index: usize, stack_ptr: u64)

Sets the stack pointer (stack_ptr) to be used when an interrupt with a corresponding IST entry in the Interrupt Descriptor table pointing to the given index is raised.

Trait Implementations

impl Clone for TaskStateSegment

fn clone(&self) -> TaskStateSegment

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for TaskStateSegment

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

Formats the value using the given formatter.

impl Default for TaskStateSegment

fn default() -> TaskStateSegment

Returns the “default value” for a type.

impl Copy for TaskStateSegment