Struct PerCpuArch 

#[repr(C)]
pub struct PerCpuArch {
    pub cpu_index: AtomicU64,
    pub user_rsp: AtomicU64,
    pub kernel_rsp: AtomicU64,
}

Minimal per-CPU block accessed from assembly via GS base.

Layout invariant (#[repr(C)]):

• cpu_index at offset 0 (8 bytes) — read by assembly as gs:[0]
• user_rsp at offset 8 (8 bytes)
• kernel_rsp at offset 16 (8 bytes)

AtomicU64 is #[repr(C, align(8))] and has the same size/alignment as u64, so the offsets declared in USER_RSP_OFFSET/KERNEL_RSP_OFFSET are preserved. The inline assembly in current_cpu_index() reads the raw 8 bytes from gs:[0], which are the inner u64 of AtomicU64.

Fields

cpu_index: AtomicU64

CPU index for this block. Written once during init via AtomicU64::store (no raw-pointer cast needed), then only ever read. AtomicU64 provides proper UnsafeCell interior mutability so reads through &PerCpuArch are not UB even though the field was written after the struct was placed in a static.

user_rsp: AtomicU64

kernel_rsp: AtomicU64