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-rw-r--r--compiler/rustc_middle/src/mir/interpret/pointer.rs15
1 files changed, 13 insertions, 2 deletions
diff --git a/compiler/rustc_middle/src/mir/interpret/pointer.rs b/compiler/rustc_middle/src/mir/interpret/pointer.rs
index 384954cbb..95e52e391 100644
--- a/compiler/rustc_middle/src/mir/interpret/pointer.rs
+++ b/compiler/rustc_middle/src/mir/interpret/pointer.rs
@@ -107,8 +107,12 @@ impl<T: HasDataLayout> PointerArithmetic for T {}
/// pointer), but `derive` adds some unnecessary bounds.
pub trait Provenance: Copy + fmt::Debug {
/// Says whether the `offset` field of `Pointer`s with this provenance is the actual physical address.
- /// If `true, ptr-to-int casts work by simply discarding the provenance.
- /// If `false`, ptr-to-int casts are not supported. The offset *must* be relative in that case.
+ /// - If `false`, the offset *must* be relative. This means the bytes representing a pointer are
+ /// different from what the Abstract Machine prescribes, so the interpreter must prevent any
+ /// operation that would inspect the underlying bytes of a pointer, such as ptr-to-int
+ /// transmutation. A `ReadPointerAsBytes` error will be raised in such situations.
+ /// - If `true`, the interpreter will permit operations to inspect the underlying bytes of a
+ /// pointer, and implement ptr-to-int transmutation by stripping provenance.
const OFFSET_IS_ADDR: bool;
/// We also use this trait to control whether to abort execution when a pointer is being partially overwritten
@@ -125,6 +129,9 @@ pub trait Provenance: Copy + fmt::Debug {
/// Otherwise this function is best-effort (but must agree with `Machine::ptr_get_alloc`).
/// (Identifying the offset in that allocation, however, is harder -- use `Memory::ptr_get_alloc` for that.)
fn get_alloc_id(self) -> Option<AllocId>;
+
+ /// Defines the 'join' of provenance: what happens when doing a pointer load and different bytes have different provenance.
+ fn join(left: Option<Self>, right: Option<Self>) -> Option<Self>;
}
impl Provenance for AllocId {
@@ -152,6 +159,10 @@ impl Provenance for AllocId {
fn get_alloc_id(self) -> Option<AllocId> {
Some(self)
}
+
+ fn join(_left: Option<Self>, _right: Option<Self>) -> Option<Self> {
+ panic!("merging provenance is not supported when `OFFSET_IS_ADDR` is false")
+ }
}
/// Represents a pointer in the Miri engine.