//! Global values.
use ir::immediates::Offset32;
use ir::{ExternalName, GlobalValue};
use std::fmt;
/// Information about a global value declaration.
#[derive(Clone)]
pub enum GlobalValueData {
/// Value is the address of a field in the VM context struct, a constant offset from the VM
/// context pointer.
VMContext {
/// Offset from the `vmctx` pointer.
offset: Offset32,
},
/// Value is pointed to by another global value.
///
/// The `base` global value is assumed to contain a pointer. This global value is computed
/// by loading from memory at that pointer value, and then adding an offset. The memory must
/// be accessible, and naturally aligned to hold a pointer value.
Deref {
/// The base pointer global value.
base: GlobalValue,
/// Byte offset to be added to the loaded value.
offset: Offset32,
},
/// Value is identified by a symbolic name. Cranelift itself does not interpret this name;
/// it's used by embedders to link with other data structures.
Sym {
/// The symbolic name.
name: ExternalName,
/// Will this symbol be defined nearby, such that it will always be a certain distance
/// away, after linking? If so, references to it can avoid going through a GOT. Note that
/// symbols meant to be preemptible cannot be colocated.
colocated: bool,
},
}
impl GlobalValueData {
/// Assume that `self` is an `GlobalValueData::Sym` and return its name.
pub fn symbol_name(&self) -> &ExternalName {
match *self {
GlobalValueData::Sym { ref name, .. } => name,
_ => panic!("only symbols have names"),
}
}
}
impl fmt::Display for GlobalValueData {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match *self {
GlobalValueData::VMContext { offset } => write!(f, "vmctx{}", offset),
GlobalValueData::Deref { base, offset } => write!(f, "deref({}){}", base, offset),
GlobalValueData::Sym {
ref name,
colocated,
} => {
if colocated {
write!(f, "colocated ")?;
}
write!(f, "globalsym {}", name)
}
}
}
}