warning: sharing memory with a native function called via FFI
  --> tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
   |
LL |     unsafe { do_one_deref(exposed) };
   |              ^^^^^^^^^^^^^^^^^^^^^ sharing memory with a native function
   |
   = help: when memory is shared with a native function call, Miri can only track initialisation and provenance on a best-effort basis
   = help: in particular, Miri assumes that the native call initializes all memory it has written to
   = help: Miri also assumes that any part of this memory may be a pointer that is permitted to point to arbitrary exposed memory
   = help: what this means is that Miri will easily miss Undefined Behavior related to incorrect usage of this shared memory, so you should not take a clean Miri run as a signal that your FFI code is UB-free
   = help: tracing memory accesses in native code is not yet fully implemented, so there can be further imprecisions beyond what is documented here
   = note: BACKTRACE:
   = note: inside `unexposed_reachable_alloc` at tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
note: inside `main`
  --> tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
   |
LL |     unexposed_reachable_alloc();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: Undefined Behavior: memory access failed: attempting to access 4 bytes, but got $HEX[noalloc] which is a dangling pointer (it has no provenance)
  --> tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
   |
LL |         let _not_ok = *invalid;
   |                       ^^^^^^^^ Undefined Behavior occurred here
   |
   = 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
   = note: BACKTRACE:
   = note: inside `unexposed_reachable_alloc` at tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
note: inside `main`
  --> tests/native-lib/fail/tracing/unexposed_reachable_alloc.rs:LL:CC
   |
LL |     unexposed_reachable_alloc();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^

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

error: aborting due to 1 previous error; 1 warning emitted