remove duplicated code, wrap WasmPtr on wasi side

lib/runtime-core/src/memory/mod.rs

@@ -10,7 +10,7 @@ use crate::{
 };
 use std::{
     cell::{Cell, RefCell},
-    fmt, mem, ptr,
+    fmt, mem,
     rc::Rc,
 };
 
@@ -21,6 +21,7 @@ pub use self::view::{Atomically, MemoryView};
 
 mod atomic;
 mod dynamic;
+pub mod ptr;
 mod static_;
 mod view;
 
@@ -221,9 +222,9 @@ struct UnsharedMemoryInternal {
 impl UnsharedMemory {
     pub fn new(desc: MemoryDescriptor) -> Result<Self, CreationError> {
         let mut local = vm::LocalMemory {
-            base: ptr::null_mut(),
+            base: std::ptr::null_mut(),
             bound: 0,
-            memory: ptr::null_mut(),
+            memory: std::ptr::null_mut(),
         };
 
         let storage = match desc.memory_type() {

lib/runtime-core/src/memory/ptr.rs

@@ -0,0 +1,125 @@
+//! A reusable pointer abstraction for getting memory from the guest's memory.
+//!
+//! This abstraction is safe: it ensures the memory is in bounds and that the pointer
+//! is aligned (avoiding undefined behavior).
+//!
+//! Therefore, you should use this abstraction whenever possible to avoid memory
+//! related bugs when implementing an ABI.
+
+use crate::{
+    memory::Memory,
+    types::{ValueType, WasmExternType},
+};
+use std::{cell::Cell, fmt, marker::PhantomData, mem};
+
+pub struct Array;
+pub struct Item;
+
+#[repr(transparent)]
+pub struct WasmPtr<T: Copy, Ty = Item> {
+    offset: u32,
+    _phantom: PhantomData<(T, Ty)>,
+}
+
+impl<T: Copy, Ty> WasmPtr<T, Ty> {
+    #[inline]
+    pub fn new(offset: u32) -> Self {
+        Self {
+            offset,
+            _phantom: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn offset(self) -> u32 {
+        self.offset
+    }
+}
+
+#[inline(always)]
+fn align_pointer(ptr: usize, align: usize) -> usize {
+    // clears bits below aligment amount (assumes power of 2) to align pointer
+    debug_assert!(align.count_ones() == 1);
+    ptr & !(align - 1)
+}
+
+impl<T: Copy + ValueType> WasmPtr<T, Item> {
+    #[inline]
+    pub fn deref<'a>(self, memory: &'a Memory) -> Option<&'a Cell<T>> {
+        if (self.offset as usize) + mem::size_of::<T>() >= memory.size().bytes().0 {
+            return None;
+        }
+        unsafe {
+            let cell_ptr = align_pointer(
+                memory.view::<u8>().as_ptr().add(self.offset as usize) as usize,
+                mem::align_of::<T>(),
+            ) as *const Cell<T>;
+            Some(&*cell_ptr)
+        }
+    }
+}
+
+impl<T: Copy + ValueType> WasmPtr<T, Array> {
+    #[inline]
+    pub fn deref<'a>(self, memory: &'a Memory, index: u32, length: u32) -> Option<&'a [Cell<T>]> {
+        // gets the size of the item in the array with padding added such that
+        // for any index, we will always result an aligned memory access
+        let item_size = mem::size_of::<T>() + (mem::size_of::<T>() % mem::align_of::<T>());
+        let slice_full_len = index as usize + length as usize;
+
+        if (self.offset as usize) + (item_size * slice_full_len) >= memory.size().bytes().0 {
+            return None;
+        }
+
+        unsafe {
+            let cell_ptr = align_pointer(
+                memory.view::<u8>().as_ptr().add(self.offset as usize) as usize,
+                mem::align_of::<T>(),
+            ) as *const Cell<T>;
+            let cell_ptrs = &std::slice::from_raw_parts(cell_ptr, slice_full_len)
+                [index as usize..slice_full_len];
+            Some(cell_ptrs)
+        }
+    }
+}
+
+unsafe impl<T: Copy, Ty> WasmExternType for WasmPtr<T, Ty> {
+    type Native = i32;
+
+    fn to_native(self) -> Self::Native {
+        self.offset as i32
+    }
+    fn from_native(n: Self::Native) -> Self {
+        Self {
+            offset: n as u32,
+            _phantom: PhantomData,
+        }
+    }
+}
+
+unsafe impl<T: Copy, Ty> ValueType for WasmPtr<T, Ty> {}
+
+impl<T: Copy, Ty> Clone for WasmPtr<T, Ty> {
+    fn clone(&self) -> Self {
+        Self {
+            offset: self.offset,
+            _phantom: PhantomData,
+        }
+    }
+}
+
+impl<T: Copy, Ty> Copy for WasmPtr<T, Ty> {}
+
+impl<T: Copy, Ty> PartialEq for WasmPtr<T, Ty> {
+    fn eq(&self, other: &Self) -> bool {
+        self.offset == other.offset
+    }
+}
+
+impl<T: Copy, Ty> Eq for WasmPtr<T, Ty> {}
+
+impl<T: Copy, Ty> fmt::Debug for WasmPtr<T, Ty> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "WasmPtr({:#x})", self.offset)
+    }
+}