Rollup merge of #126787 - Strophox:get-bytes, r=RalfJung

Add direct accessors for memory addresses in `Machine` (for Miri)

The purpose of this PR is to enable direct (immutable) access to memory addresses in `Machine`, which will be needed for further extension of Miri.

This is done by adding (/completing missings pairs of) accessor functions, with the relevant signatures as follows:
```rust
/* rust/compiler/rustc_middle/src/mir/interpret/allocation.rs */

pub trait AllocBytes {
  // ..

  fn as_ptr(&self) -> *const u8;
/*fn as_mut_ptr(&mut self) -> *mut u8; -- Already in the compiler*/
}

impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes> {
  // ..

  pub fn get_bytes_unchecked_raw(&self) -> *const u8;
/*pub fn get_bytes_unchecked_raw_mut(&mut self) -> *mut u8; -- Already in the compiler*/
}
```
```rust
/* rust/compiler/rustc_const_eval/src/interpret/memory.rs */

impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
  // ..

  pub fn get_alloc_bytes_unchecked_raw(&self, id: AllocId) -> InterpResult<'tcx, *const u8>;
  pub fn get_alloc_bytes_unchecked_raw_mut(&mut self, id: AllocId) -> InterpResult<'tcx, *mut u8>;
}
```

r? ``@RalfJung``

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -630,6 +630,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
     }
 
+    /// Gives raw, immutable access to the `Allocation` address, without bounds or alignment checks.
+    /// The caller is responsible for calling the access hooks!
+    pub fn get_alloc_bytes_unchecked_raw(&self, id: AllocId) -> InterpResult<'tcx, *const u8> {
+        let alloc = self.get_alloc_raw(id)?;
+        Ok(alloc.get_bytes_unchecked_raw())
+    }
+
     /// Bounds-checked *but not align-checked* allocation access.
     pub fn get_ptr_alloc<'a>(
         &'a self,
@@ -713,6 +720,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         Ok((alloc, &mut self.machine))
     }
 
+    /// Gives raw, mutable access to the `Allocation` address, without bounds or alignment checks.
+    /// The caller is responsible for calling the access hooks!
+    pub fn get_alloc_bytes_unchecked_raw_mut(
+        &mut self,
+        id: AllocId,
+    ) -> InterpResult<'tcx, *mut u8> {
+        let alloc = self.get_alloc_raw_mut(id)?.0;
+        Ok(alloc.get_bytes_unchecked_raw_mut())
+    }
+
     /// Bounds-checked *but not align-checked* allocation access.
     pub fn get_ptr_alloc_mut<'a>(
         &'a mut self,

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -40,9 +40,16 @@ pub trait AllocBytes: Clone + fmt::Debug + Deref<Target = [u8]> + DerefMut<Targe
     /// Gives direct access to the raw underlying storage.
     ///
     /// Crucially this pointer is compatible with:
-    /// - other pointers retunred by this method, and
+    /// - other pointers returned by this method, and
     /// - references returned from `deref()`, as long as there was no write.
     fn as_mut_ptr(&mut self) -> *mut u8;
+
+    /// Gives direct access to the raw underlying storage.
+    ///
+    /// Crucially this pointer is compatible with:
+    /// - other pointers returned by this method, and
+    /// - references returned from `deref()`, as long as there was no write.
+    fn as_ptr(&self) -> *const u8;
 }
 
 /// Default `bytes` for `Allocation` is a `Box<u8>`.
@@ -62,6 +69,11 @@ impl AllocBytes for Box<[u8]> {
         // Carefully avoiding any intermediate references.
         ptr::addr_of_mut!(**self).cast()
     }
+
+    fn as_ptr(&self) -> *const u8 {
+        // Carefully avoiding any intermediate references.
+        ptr::addr_of!(**self).cast()
+    }
 }
 
 /// This type represents an Allocation in the Miri/CTFE core engine.
@@ -490,19 +502,27 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         self.provenance.clear(range, cx)?;
 
         assert!(range.end().bytes_usize() <= self.bytes.len()); // need to do our own bounds-check
-        // Cruciall, we go via `AllocBytes::as_mut_ptr`, not `AllocBytes::deref_mut`.
+        // Crucially, we go via `AllocBytes::as_mut_ptr`, not `AllocBytes::deref_mut`.
         let begin_ptr = self.bytes.as_mut_ptr().wrapping_add(range.start.bytes_usize());
         let len = range.end().bytes_usize() - range.start.bytes_usize();
         Ok(ptr::slice_from_raw_parts_mut(begin_ptr, len))
     }
 
     /// This gives direct mutable access to the entire buffer, just exposing their internal state
-    /// without reseting anything. Directly exposes `AllocBytes::as_mut_ptr`. Only works if
+    /// without resetting anything. Directly exposes `AllocBytes::as_mut_ptr`. Only works if
     /// `OFFSET_IS_ADDR` is true.
     pub fn get_bytes_unchecked_raw_mut(&mut self) -> *mut u8 {
         assert!(Prov::OFFSET_IS_ADDR);
         self.bytes.as_mut_ptr()
     }
+
+    /// This gives direct immutable access to the entire buffer, just exposing their internal state
+    /// without resetting anything. Directly exposes `AllocBytes::as_ptr`. Only works if
+    /// `OFFSET_IS_ADDR` is true.
+    pub fn get_bytes_unchecked_raw(&self) -> *const u8 {
+        assert!(Prov::OFFSET_IS_ADDR);
+        self.bytes.as_ptr()
+    }
 }
 
 /// Reading and writing.

src/tools/miri/src/alloc_bytes.rs

@@ -108,4 +108,8 @@ impl AllocBytes for MiriAllocBytes {
     fn as_mut_ptr(&mut self) -> *mut u8 {
         self.ptr
     }
+
+    fn as_ptr(&self) -> *const u8 {
+        self.ptr
+    }
 }