Rollup merge of #96162 - RalfJung:mark-uninit, r=oli-obk

interpret: Fix writing uninit to an allocation

When calling `mark_init`, we need to also be mindful of what happens with the relocations! Specifically, when we de-init memory, we need to clear relocations in that range as well or else strange things will happen (and printing will not show the de-init, since relocations take precedence there).

Fixes https://github.com/rust-lang/miri/issues/2068.

Here's the Miri testcase that this fixes (requires `-Zmiri-disable-validation`):
```rust
use std::mem::MaybeUninit;

fn main() { unsafe {
    let mut x = MaybeUninit::<i64>::uninit();
    // Put in a ptr.
    x.as_mut_ptr().cast::<&i32>().write_unaligned(&0);
    // Overwrite parts of that pointer with 'uninit' through a Scalar.
    let ptr = x.as_mut_ptr().cast::<i32>();
    *ptr = MaybeUninit::uninit().assume_init();
    // Reading this back should hence work fine.
    let _c = *ptr;
} }
```
Previously this failed with
```
error: unsupported operation: unable to turn pointer into raw bytes
  --> ../miri/uninit.rs:11:14
   |
11 |     let _c = *ptr;
   |              ^^^^ unable to turn pointer into raw bytes
   |
   = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support

   = note: inside `main` at ../miri/uninit.rs:11:14
```

2 files changed, 10 insertions, 5 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index a165fa23f30..9ae50d0df80 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -892,8 +892,11 @@ impl<'tcx, 'a, Tag: Provenance, Extra> AllocRefMut<'a, 'tcx, Tag, Extra> {
     }
 
     /// Mark the entire referenced range as uninitalized
-    pub fn write_uninit(&mut self) {
-        self.alloc.mark_init(self.range, false);
+    pub fn write_uninit(&mut self) -> InterpResult<'tcx> {
+        Ok(self
+            .alloc
+            .write_uninit(&self.tcx, self.range)
+            .map_err(|e| e.to_interp_error(self.alloc_id))?)
     }
 }
 
@@ -1053,8 +1056,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             // This also avoids writing to the target bytes so that the backing allocation is never
             // touched if the bytes stay uninitialized for the whole interpreter execution. On contemporary
             // operating system this can avoid physically allocating the page.
-            dest_alloc.mark_init(dest_range, false); // `Size` multiplication
-            dest_alloc.mark_relocation_range(relocations);
+            dest_alloc
+                .write_uninit(&tcx, dest_range)
+                .map_err(|e| e.to_interp_error(dest_alloc_id))?;
+            // We can forget about the relocations, this is all not initialized anyway.
             return Ok(());
         }
 
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index 31da4522a1f..e4660fe090c 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -823,7 +823,7 @@ where
             // Zero-sized access
             return Ok(());
         };
-        alloc.write_uninit();
+        alloc.write_uninit()?;
         Ok(())
     }