Struct cranelift_codegen::binemit::StackMap
source · [−]pub struct StackMap { /* private fields */ }
Expand description
Stack maps record which words in a stack frame contain live GC references at a given instruction pointer.
Logically, a set of stack maps for a function record a table of the form:
+---------------------+-------------------------------------------+
| Instruction Pointer | SP-Relative Offsets of Live GC References |
+---------------------+-------------------------------------------+
| 0x12345678 | 2, 6, 12 |
| 0x1234abcd | 2, 6 |
| ... | ... |
+---------------------+-------------------------------------------+
Where “instruction pointer” is an instruction pointer within the function, and “offsets of live GC references” contains the offsets (in units of words) from the frame’s stack pointer where live GC references are stored on the stack. Instruction pointers within the function that do not have an entry in this table are not GC safepoints.
Because
- offsets of live GC references are relative from the stack pointer, and
- stack frames grow down from higher addresses to lower addresses,
to get a pointer to a live reference at offset x
within a stack frame, you
add x
from the frame’s stack pointer.
For example, to calculate the pointer to the live GC reference inside “frame
1” below, you would do frame_1_sp + x
:
Stack
+-------------------+
| Frame 0 |
| |
| | |
| +-------------------+ <--- Frame 0's SP
| | Frame 1 |
Grows | |
down | |
| | Live GC reference | --+--
| | | |
| | | |
V | | x = offset of live GC reference
| | |
| | |
+-------------------+ --+-- <--- Frame 1's SP
| Frame 2 |
| ... |
An individual StackMap
is associated with just one instruction pointer
within the function, contains the size of the stack frame, and represents
the stack frame as a bitmap. There is one bit per word in the stack frame,
and if the bit is set, then the word contains a live GC reference.
Note that a caller’s OutgoingArg
stack slots and callee’s IncomingArg
stack slots overlap, so we must choose which function’s stack maps record
live GC references in these slots. We record the IncomingArg
s in the
callee’s stack map.
Implementations
sourceimpl StackMap
impl StackMap
Trait Implementations
impl Eq for StackMap
impl StructuralEq for StackMap
impl StructuralPartialEq for StackMap
Auto Trait Implementations
impl RefUnwindSafe for StackMap
impl Send for StackMap
impl Sync for StackMap
impl Unpin for StackMap
impl UnwindSafe for StackMap
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<Q, K> Equivalent<K> for Q where
Q: Eq + ?Sized,
K: Borrow<Q> + ?Sized,
impl<Q, K> Equivalent<K> for Q where
Q: Eq + ?Sized,
K: Borrow<Q> + ?Sized,
sourcefn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
Compare self to key
and return true
if they are equal.
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
toowned_clone_into
)Uses borrowed data to replace owned data, usually by cloning. Read more