Struct TaskContext

pub struct TaskContext {
    pub kstack_top: VirtAddr,
    pub rsp: u64,
    pub fs_base: usize,
    pub gs_base: usize,
    pub ext_state: ExtendedState,
    pub cr3: PhysAddr,
}

Saved hardware states of a task.

The context usually includes:

• Callee-saved registers
• Stack pointer register
• Thread pointer register (for kernel space thread-local storage)
• FP/SIMD registers

On context switch, current task saves its context from CPU to memory, and the next task restores its context from memory to CPU.

On x86_64, callee-saved registers are saved to the kernel stack by the PUSH instruction. So that rsp is the RSP after callee-saved registers are pushed, and kstack_top is the top of the kernel stack (RSP before any push).

Fields

kstack_top: VirtAddr

The kernel stack top of the task.

rsp: u64

RSP after all callee-saved registers are pushed.

fs_base: usize

Thread pointer (FS segment base address)

gs_base: usize

Available on crate feature uspace only.

User space Thread pointer (GS segment base address)

During task switching, it is written to KernelGSBase MSR.

ext_state: ExtendedState

Available on crate feature fp_simd only.

Extended states, i.e., FP/SIMD states.

cr3: PhysAddr

Available on crate feature uspace only.

The CR3 register value, i.e., the page table root.

Implementations

impl TaskContext

pub fn new() -> Self

Creates a dummy context for a new task.

Note the context is not initialized, it will be filled by switch_to (for initial tasks) and init (for regular tasks) methods.

pub fn init(&mut self, entry: usize, kstack_top: VirtAddr, tls_area: VirtAddr)

Initializes the context for a new task, with the given entry point and kernel stack.

pub fn set_page_table_root(&mut self, cr3: PhysAddr)

Available on crate feature uspace only.

Changes the page table root (CR3 register for x86_64).

If not set, the kernel page table root is used (obtained by axhal::paging::kernel_page_table_root).

pub fn switch_to(&mut self, next_ctx: &Self)

Switches to another task.

It first saves the current task’s context from CPU to this place, and then restores the next task’s context from next_ctx to CPU.

Trait Implementations

impl Debug for TaskContext

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

Formats the value using the given formatter.