error: Undefined Behavior: memory access failed: ALLOC has been freed, so this pointer is dangling
  --> $DIR/zst2.rs:LL:CC
   |
LL |     unsafe { *x = zst_val };
   |              ^^^^^^^^^^^^ memory access failed: ALLOC has been freed, so this pointer is dangling
   |
   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
help: ALLOC was allocated here:
  --> $DIR/zst2.rs:LL:CC
   |
LL |     let mut x_box = Box::new(1u8);
   |                     ^^^^^^^^^^^^^
help: ALLOC was deallocated here:
  --> $DIR/zst2.rs:LL:CC
   |
LL |     drop(x_box);
   |     ^^^^^^^^^^^
   = note: BACKTRACE (of the first span):
   = note: inside `main` at $DIR/zst2.rs:LL:CC

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to 1 previous error