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Contents
use crate::{isa::x64::inst::regs, machinst::Reg};
/// The `stack_switch` instruction loads information about the stack to switch
/// to and stores information about the current stack by receiving pointers to
/// memory laid out as in the struct `ControlContext` below.
///
/// The instruction is only supported on x64 Linux at the moment.
///
/// ```
/// #[repr(C)]
/// pub struct ControlContext {
/// pub stack_pointer: *mut u8,
/// pub frame_pointer: *mut u8,
/// pub instruction_pointer: *mut u8,
/// }
/// ```
///
/// Note that this layout is deliberately chosen to make frame pointer walking
/// possible, if desired: The layout enables stack layouts where a
/// `ControlContext` is part of a frame pointer chain, putting the frame pointer
/// next to the corresponding IP.
///
/// We never actually interact with values of that type in Cranelift, but are
/// only interested in its layout for the purposes of generating code.
#[allow(dead_code)]
pub struct ControlContextLayout {
pub size: usize,
pub stack_pointer_offset: usize,
pub frame_pointer_offset: usize,
pub ip_offset: usize,
}
pub fn control_context_layout() -> ControlContextLayout {
ControlContextLayout {
size: 24,
stack_pointer_offset: 0,
frame_pointer_offset: 8,
ip_offset: 16,
}
}
/// The register used for handing over the payload when switching stacks.
///
/// We must use a fixed register for sending and receiving the payload: When
/// switching from one stack to another using two matching``stack_switch``
/// instructions, they must agree on the register where the payload is, similar
/// to a calling convention. The same holds when `stack_switch`-ing to a newly
/// initialized stack, where the entry trampoline must know which register the
/// payload is in.
pub fn payload_register() -> Reg {
regs::rdi()
}
Version data entries
7 entries across 7 versions & 1 rubygems