adjust for ERR_ON_PARTIAL_PTR_OVERWRITE

Author: RalfJung

src/machine.rs

@@ -128,8 +128,12 @@ pub struct Tag {
 }
 
 impl Provenance for Tag {
+    // We use absolute addresses in the `offset` of a `Pointer<Tag>`.
     const OFFSET_IS_ADDR: bool = true;
 
+    // We cannot err on partial overwrites, it happens too often in practice (due to unions).
+    const ERR_ON_PARTIAL_PTR_OVERWRITE: bool = false;
+
     fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let (tag, addr) = ptr.into_parts(); // address is absolute
         write!(f, "0x{:x}", addr.bytes())?;

tests/compile-fail/overwriting_part_of_relocation_makes_the_rest_uninit.rs renamed to tests/compile-fail/pointer_partial_overwrite.rs

@@ -1,6 +1,9 @@
 // Make sure we find these even with many checks disabled.
 // compile-flags: -Zmiri-disable-alignment-check -Zmiri-disable-stacked-borrows -Zmiri-disable-validation
 
+// Test what happens when we overwrite parts of a pointer.
+// Also see <https://github.com/rust-lang/rust/issues/87184>.
+
 fn main() {
     let mut p = &42;
     unsafe {

tests/compile-fail/pointer_byte_read.rs renamed to tests/compile-fail/pointer_partial_read.rs

@@ -1,3 +1,5 @@
+// Test what happens when we read parts of a pointer.
+// Related to <https://github.com/rust-lang/rust/issues/69488>.
 fn main() {
     let x = 13;
     let y = &x;