Add Pages and Bytes newtypes

lib/clif-backend/src/func_env.rs

@@ -13,8 +13,6 @@ use wasmer_runtime_core::{
     vm,
 };
 
-const WASM_PAGE_SIZE: usize = 65_536;
-
 pub struct FuncEnv<'env, 'module, 'isa> {
     env: &'env ModuleEnv<'module, 'isa>,
 }
@@ -219,7 +217,7 @@ impl<'env, 'module, 'isa> FuncEnvironment for FuncEnv<'env, 'module, 'isa> {
 
                 func.create_heap(ir::HeapData {
                     base: local_memory_base,
-                    min_size: ((description.minimum as u64) * (WASM_PAGE_SIZE as u64)).into(),
+                    min_size: (description.minimum.bytes().0 as u64).into(),
                     offset_guard_size: mem_type.guard_size().into(),
                     style: ir::HeapStyle::Dynamic {
                         bound_gv: local_memory_bound,
@@ -230,7 +228,7 @@ impl<'env, 'module, 'isa> FuncEnvironment for FuncEnv<'env, 'module, 'isa> {
             mem_type @ MemoryType::Static | mem_type @ MemoryType::SharedStatic => func
                 .create_heap(ir::HeapData {
                     base: local_memory_base,
-                    min_size: ((description.minimum as u64) * (WASM_PAGE_SIZE as u64)).into(),
+                    min_size: (description.minimum.bytes().0 as u64).into(),
                     offset_guard_size: mem_type.guard_size().into(),
                     style: ir::HeapStyle::Static {
                         bound: mem_type.bounds().unwrap().into(),

lib/clif-backend/src/module_env.rs

@@ -14,6 +14,7 @@ use wasmer_runtime_core::{
         ElementType, FuncSig, GlobalDescriptor, GlobalIndex, GlobalInit, Initializer,
         LocalFuncIndex, LocalOrImport, MemoryDescriptor, SigIndex, TableDescriptor, Value,
     },
+    units::Pages,
 };
 
 pub struct ModuleEnv<'module, 'isa> {
@@ -251,8 +252,8 @@ impl<'module, 'isa, 'data> ModuleEnvironment<'data> for ModuleEnv<'module, 'isa>
     /// Declares a memory to the environment
     fn declare_memory(&mut self, memory: cranelift_wasm::Memory) {
         self.module.memories.push(MemoryDescriptor {
-            minimum: memory.minimum,
+            minimum: Pages(memory.minimum),
-            maximum: memory.maximum,
+            maximum: memory.maximum.map(|max| Pages(max)),
             shared: memory.shared,
         });
     }
@@ -270,8 +271,8 @@ impl<'module, 'isa, 'data> ModuleEnvironment<'data> for ModuleEnv<'module, 'isa>
         };
 
         let memory = MemoryDescriptor {
-            minimum: memory.minimum,
+            minimum: Pages(memory.minimum),
-            maximum: memory.maximum,
+            maximum: memory.maximum.map(|max| Pages(max)),
             shared: memory.shared,
         };
 

lib/runtime-core/examples/simple/main.rs

@@ -7,6 +7,7 @@ use wasmer_runtime_core::{
     prelude::*,
     table::Table,
     types::{ElementType, MemoryDescriptor, TableDescriptor, Value},
+    units::Pages,
 };
 
 static EXAMPLE_WASM: &'static [u8] = include_bytes!("simple.wasm");
@@ -16,8 +17,8 @@ fn main() -> Result<()> {
     let inner_module = wasmer_runtime_core::compile_with(&wasm_binary, &CraneliftCompiler::new())?;
 
     let memory = Memory::new(MemoryDescriptor {
-        min: 1,
+        minimum: Pages(1),
-        max: Some(1),
+        maximum: Some(Pages(1)),
         shared: false,
     })
     .unwrap();
@@ -26,8 +27,8 @@ fn main() -> Result<()> {
 
     let table = Table::new(TableDescriptor {
         element: ElementType::Anyfunc,
-        min: 10,
+        minimum: 10,
-        max: None,
+        maximum: None,
     })
     .unwrap();
 

lib/runtime-core/src/backing.rs

@@ -3,7 +3,7 @@ use crate::{
     export::{Context, Export},
     global::Global,
     import::ImportObject,
-    memory::{Memory, WASM_PAGE_SIZE},
+    memory::Memory,
     module::{ImportName, ModuleInner},
     structures::{BoxedMap, Map, SliceMap, TypedIndex},
     table::Table,
@@ -104,7 +104,7 @@ impl LocalBacking {
                 LocalOrImport::Local(local_memory_index) => {
                     let memory_desc = module.memories[local_memory_index];
                     let data_top = init_base + init.data.len();
-                    assert!(memory_desc.minimum as usize * WASM_PAGE_SIZE >= data_top);
+                    assert!(memory_desc.minimum.bytes().0 >= data_top);
 
                     let mem = &memories[local_memory_index];
                     mem.write_many(init_base as u32, &init.data).unwrap();
@@ -167,9 +167,8 @@ impl LocalBacking {
                 LocalOrImport::Local(local_table_index) => {
                     let table = &tables[local_table_index];
 
-                    if (table.current_size() as usize) < init_base + init.elements.len() {
+                    if (table.size() as usize) < init_base + init.elements.len() {
-                        let delta =
+                        let delta = (init_base + init.elements.len()) - table.size() as usize;
-                            (init_base + init.elements.len()) - table.current_size() as usize;
                         // Grow the table if it's too small.
                         table.grow(delta as u32).expect("couldn't grow table");
                     }
@@ -203,9 +202,8 @@ impl LocalBacking {
                 LocalOrImport::Import(import_table_index) => {
                     let table = &imports.tables[import_table_index];
 
-                    if (table.current_size() as usize) < init_base + init.elements.len() {
+                    if (table.size() as usize) < init_base + init.elements.len() {
-                        let delta =
+                        let delta = (init_base + init.elements.len()) - table.size() as usize;
-                            (init_base + init.elements.len()) - table.current_size() as usize;
                         // Grow the table if it's too small.
                         table.grow(delta as u32).expect("couldn't grow table");
                     }

lib/runtime-core/src/error.rs

@@ -140,6 +140,20 @@ impl PartialEq for CallError {
     }
 }
 
+/// This error type is produced when creating something,
+/// like a `Memory` or a `Table`.
+#[derive(Debug, Clone)]
+pub enum CreationError {
+    UnableToCreateMemory,
+    UnableToCreateTable,
+}
+
+impl PartialEq for CreationError {
+    fn eq(&self, _other: &CreationError) -> bool {
+        false
+    }
+}
+
 /// The amalgamation of all errors that can occur
 /// during the compilation, instantiation, or execution
 /// of a webassembly module.
@@ -152,6 +166,7 @@ pub enum Error {
     RuntimeError(RuntimeError),
     ResolveError(ResolveError),
     CallError(CallError),
+    CreationError(CreationError),
 }
 
 impl PartialEq for Error {
@@ -220,6 +235,12 @@ impl From<CallError> for Box<Error> {
     }
 }
 
+impl From<CreationError> for Box<Error> {
+    fn from(creation_err: CreationError) -> Self {
+        Box::new(Error::CreationError(creation_err))
+    }
+}
+
 impl From<RuntimeError> for Box<CallError> {
     fn from(runtime_err: RuntimeError) -> Self {
         Box::new(CallError::Runtime(runtime_err))

lib/runtime-core/src/global.rs

@@ -12,10 +12,28 @@ pub struct Global {
 }
 
 impl Global {
+    /// Create a new `Global` value.
+    ///
+    /// Usage:
+    ///
+    /// ```
+    /// # use wasmer_runtime_core::global::Global;
+    /// # use wasmer_runtime_core::types::Value;
+    /// let global = Global::new(Value::I32(42));
+    /// ```
     pub fn new(value: Value) -> Self {
         Self::new_internal(value, false)
     }
 
+    /// Create a new, mutable `Global` value.
+    ///
+    /// Usage:
+    ///
+    /// ```
+    /// # use wasmer_runtime_core::global::Global;
+    /// # use wasmer_runtime_core::types::Value;
+    /// let global = Global::new_mutable(Value::I32(42));
+    /// ```
     pub fn new_mutable(value: Value) -> Self {
         Self::new_internal(value, true)
     }
@@ -41,10 +59,17 @@ impl Global {
         }
     }
 
+    /// Get the [`GlobalDescriptor`] generated for this global.
+    ///
+    /// [`GlobalDescriptor`]: struct.GlobalDescriptor.html
     pub fn descriptor(&self) -> GlobalDescriptor {
         self.desc
     }
 
+    /// Set the value help by this global.
+    ///
+    /// This method will panic if the value is
+    /// the wrong type.
     pub fn set(&self, value: Value) {
         if self.desc.mutable {
             if self.desc.ty == value.ty() {
@@ -65,6 +90,7 @@ impl Global {
         }
     }
 
+    /// Get the value held by this global.
     pub fn get(&self) -> Value {
         let data = self.storage.borrow().data;
 

lib/runtime-core/src/lib.rs

@@ -19,6 +19,7 @@ pub mod structures;
 mod sys;
 pub mod table;
 pub mod types;
+pub mod units;
 pub mod vm;
 #[doc(hidden)]
 pub mod vmcalls;

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

@@ -1,7 +1,8 @@
 use crate::{
-    memory::{WASM_MAX_PAGES, WASM_PAGE_SIZE},
+    error::CreationError,
     sys,
     types::MemoryDescriptor,
+    units::{Bytes, Pages},
     vm,
 };
 
@@ -22,24 +23,24 @@ pub const DYNAMIC_GUARD_SIZE: usize = 4096;
 /// us to add a guard-page at the end to help elide some bounds-checks.
 pub struct DynamicMemory {
     memory: sys::Memory,
-    current: u32,
+    current: Pages,
-    max: Option<u32>,
+    max: Option<Pages>,
 }
 
 impl DynamicMemory {
-    pub(super) fn new(desc: MemoryDescriptor, local: &mut vm::LocalMemory) -> Option<Box<Self>> {
+    pub(super) fn new(
+        desc: MemoryDescriptor,
+        local: &mut vm::LocalMemory,
+    ) -> Result<Box<Self>, CreationError> {
+        let min_bytes: Bytes = desc.minimum.into();
         let memory = {
-            let mut memory =
+            let mut memory = sys::Memory::with_size(min_bytes.0 + DYNAMIC_GUARD_SIZE)
-                sys::Memory::with_size((desc.minimum as usize * WASM_PAGE_SIZE) + DYNAMIC_GUARD_SIZE)
+                .map_err(|_| CreationError::UnableToCreateMemory)?;
-                    .ok()?;
+            if desc.minimum != Pages(0) {
-            if desc.minimum != 0 {
                 unsafe {
                     memory
-                        .protect(
+                        .protect(0..min_bytes.0, sys::Protect::ReadWrite)
-                            0..(desc.minimum as usize * WASM_PAGE_SIZE),
+                        .map_err(|_| CreationError::UnableToCreateMemory)?;
-                            sys::Protect::ReadWrite,
-                        )
-                        .ok()?;
                 }
             }
 
@@ -54,18 +55,18 @@ impl DynamicMemory {
         let storage_ptr: *mut DynamicMemory = &mut *storage;
 
         local.base = storage.memory.as_ptr();
-        local.bound = desc.minimum as usize * WASM_PAGE_SIZE;
+        local.bound = min_bytes.0;
         local.memory = storage_ptr as *mut ();
 
-        Some(storage)
+        Ok(storage)
     }
 
-    pub fn current(&self) -> u32 {
+    pub fn size(&self) -> Pages {
         self.current
     }
 
-    pub fn grow(&mut self, delta: u32, local: &mut vm::LocalMemory) -> Option<u32> {
+    pub fn grow(&mut self, delta: Pages, local: &mut vm::LocalMemory) -> Option<Pages> {
-        if delta == 0 {
+        if delta == Pages(0) {
             return Some(self.current);
         }
 
@@ -77,30 +78,22 @@ impl DynamicMemory {
             }
         }
 
-        if new_pages as usize > WASM_MAX_PAGES {
-            return None;
-        }
-
         let mut new_memory =
-            sys::Memory::with_size((new_pages as usize * WASM_PAGE_SIZE) + DYNAMIC_GUARD_SIZE)
+            sys::Memory::with_size(new_pages.bytes().0 + DYNAMIC_GUARD_SIZE).ok()?;
-                .ok()?;
 
         unsafe {
             new_memory
-                .protect(
+                .protect(0..new_pages.bytes().0, sys::Protect::ReadWrite)
-                    0..(new_pages as usize * WASM_PAGE_SIZE),
-                    sys::Protect::ReadWrite,
-                )
                 .ok()?;
 
-            new_memory.as_slice_mut()[..self.current as usize * WASM_PAGE_SIZE]
+            new_memory.as_slice_mut()[..self.current.bytes().0]
-                .copy_from_slice(&self.memory.as_slice()[..self.current as usize * WASM_PAGE_SIZE]);
+                .copy_from_slice(&self.memory.as_slice()[..self.current.bytes().0]);
         }
 
         self.memory = new_memory; //The old memory gets dropped.
 
         local.base = self.memory.as_ptr();
-        local.bound = new_pages as usize * WASM_PAGE_SIZE;
+        local.bound = new_pages.bytes().0;
 
         let old_pages = self.current;
         self.current = new_pages;
@@ -108,10 +101,10 @@ impl DynamicMemory {
     }
 
     pub fn as_slice(&self) -> &[u8] {
-        unsafe { &self.memory.as_slice()[0..self.current as usize * WASM_PAGE_SIZE] }
+        unsafe { &self.memory.as_slice()[0..self.current.bytes().0] }
     }
 
     pub fn as_slice_mut(&mut self) -> &mut [u8] {
-        unsafe { &mut self.memory.as_slice_mut()[0..self.current as usize * WASM_PAGE_SIZE] }
+        unsafe { &mut self.memory.as_slice_mut()[0..self.current.bytes().0] }
     }
 }

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

@@ -1,9 +1,11 @@
 use crate::{
+    error::CreationError,
     export::Export,
     import::IsExport,
     memory::dynamic::DYNAMIC_GUARD_SIZE,
     memory::static_::{SAFE_STATIC_GUARD_SIZE, SAFE_STATIC_HEAP_SIZE},
     types::{MemoryDescriptor, ValueType},
+    units::Pages,
     vm,
 };
 use std::{cell::RefCell, fmt, mem, ptr, rc::Rc, slice};
@@ -14,9 +16,6 @@ pub use self::static_::{SharedStaticMemory, StaticMemory};
 mod dynamic;
 mod static_;
 
-pub const WASM_PAGE_SIZE: usize = 65_536;
-pub const WASM_MAX_PAGES: usize = 65_536;
-
 pub struct Memory {
     desc: MemoryDescriptor,
     storage: Rc<RefCell<(MemoryStorage, Box<vm::LocalMemory>)>>,
@@ -24,29 +23,28 @@ pub struct Memory {
 
 impl Memory {
     /// Create a new `Memory` from a [`MemoryDescriptor`]
-    /// 
+    ///
     /// [`MemoryDescriptor`]: struct.MemoryDescriptor.html
-    /// 
+    ///
     /// Usage:
-    /// 
+    ///
     /// ```
     /// # use wasmer_runtime_core::types::MemoryDescriptor;
     /// # use wasmer_runtime_core::memory::Memory;
     /// # use wasmer_runtime_core::error::Result;
-    /// 
+    /// # use wasmer_runtime_core::units::Pages;
     /// # fn create_memory() -> Result<()> {
     /// let descriptor = MemoryDescriptor {
-    ///     minimum: 10,
+    ///     minimum: Pages(10),
     ///     maximum: None,
     ///     shared: false,
     /// };
-    /// 
+    ///
     /// let memory = Memory::new(descriptor)?;
-    /// 
     /// # Ok(())
     /// # }
     /// ```
-    pub fn new(desc: MemoryDescriptor) -> Option<Self> {
+    pub fn new(desc: MemoryDescriptor) -> Result<Self, CreationError> {
         let mut vm_local_memory = Box::new(vm::LocalMemory {
             base: ptr::null_mut(),
             bound: 0,
@@ -63,7 +61,7 @@ impl Memory {
             MemoryType::SharedStatic => unimplemented!("shared memories are not yet implemented"),
         };
 
-        Some(Memory {
+        Ok(Memory {
             desc,
             storage: Rc::new(RefCell::new((memory_storage, vm_local_memory))),
         })
@@ -71,14 +69,14 @@ impl Memory {
 
     /// Return the [`MemoryDescriptor`] that this memory
     /// was created with.
-    /// 
+    ///
     /// [`MemoryDescriptor`]: struct.MemoryDescriptor.html
     pub fn descriptor(&self) -> MemoryDescriptor {
         self.desc
     }
 
     /// Grow this memory by the specfied number of pages.
-    pub fn grow(&mut self, delta: u32) -> Option<u32> {
+    pub fn grow(&mut self, delta: Pages) -> Option<Pages> {
         match &mut *self.storage.borrow_mut() {
             (MemoryStorage::Dynamic(ref mut dynamic_memory), ref mut local) => {
                 dynamic_memory.grow(delta, local)
@@ -90,16 +88,11 @@ impl Memory {
         }
     }
 
-    /// The size, in bytes, of this memory.
-    pub fn bytes(&self) -> usize {
-        (self.size() as usize) * WASM_PAGE_SIZE
-    }
-
     /// The size, in wasm pages, of this memory.
-    pub fn size(&self) -> u32 {
+    pub fn size(&self) -> Pages {
         match &*self.storage.borrow() {
-            (MemoryStorage::Dynamic(ref dynamic_memory), _) => dynamic_memory.current(),
+            (MemoryStorage::Dynamic(ref dynamic_memory), _) => dynamic_memory.size(),
-            (MemoryStorage::Static(ref static_memory), _) => static_memory.current(),
+            (MemoryStorage::Static(ref static_memory), _) => static_memory.size(),
             (MemoryStorage::SharedStatic(_), _) => unimplemented!(),
         }
     }
@@ -304,7 +297,7 @@ impl fmt::Debug for Memory {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Memory")
             .field("desc", &self.desc)
-            .field("size", &self.bytes())
+            .field("size", &self.size())
             .finish()
     }
 }

lib/runtime-core/src/memory/static_/unshared.rs

@@ -1,10 +1,9 @@
 use crate::{
-    memory::{
+    error::CreationError,
-        static_::{SAFE_STATIC_GUARD_SIZE, SAFE_STATIC_HEAP_SIZE},
+    memory::static_::{SAFE_STATIC_GUARD_SIZE, SAFE_STATIC_HEAP_SIZE},
-        WASM_MAX_PAGES, WASM_PAGE_SIZE,
-    },
     sys,
     types::MemoryDescriptor,
+    units::Pages,
     vm,
 };
 
@@ -21,26 +20,23 @@ use crate::{
 /// allows them to select the type of memory used however.
 pub struct StaticMemory {
     memory: sys::Memory,
-    current: u32,
+    current: Pages,
-    max: Option<u32>,
+    max: Option<Pages>,
 }
 
 impl StaticMemory {
     pub(in crate::memory) fn new(
         desc: MemoryDescriptor,
         local: &mut vm::LocalMemory,
-    ) -> Option<Box<Self>> {
+    ) -> Result<Box<Self>, CreationError> {
         let memory = {
-            let mut memory =
+            let mut memory = sys::Memory::with_size(SAFE_STATIC_HEAP_SIZE + SAFE_STATIC_GUARD_SIZE)
-                sys::Memory::with_size(SAFE_STATIC_HEAP_SIZE + SAFE_STATIC_GUARD_SIZE).ok()?;
+                .map_err(|_| CreationError::UnableToCreateMemory)?;
-            if desc.minimum != 0 {
+            if desc.minimum != Pages(0) {
                 unsafe {
                     memory
-                        .protect(
+                        .protect(0..desc.minimum.bytes().0, sys::Protect::ReadWrite)
-                            0..(desc.minimum as usize * WASM_PAGE_SIZE),
+                        .map_err(|_| CreationError::UnableToCreateMemory)?;
-                            sys::Protect::ReadWrite,
-                        )
-                        .ok()?;
                 }
             }
 
@@ -55,18 +51,18 @@ impl StaticMemory {
         let storage_ptr: *mut StaticMemory = &mut *storage;
 
         local.base = storage.memory.as_ptr();
-        local.bound = desc.minimum as usize * WASM_PAGE_SIZE;
+        local.bound = desc.minimum.bytes().0;
         local.memory = storage_ptr as *mut ();
 
-        Some(storage)
+        Ok(storage)
     }
 
-    pub fn current(&self) -> u32 {
+    pub fn size(&self) -> Pages {
         self.current
     }
 
-    pub fn grow(&mut self, delta: u32, local: &mut vm::LocalMemory) -> Option<u32> {
+    pub fn grow(&mut self, delta: Pages, local: &mut vm::LocalMemory) -> Option<Pages> {
-        if delta == 0 {
+        if delta == Pages(0) {
             return Some(self.current);
         }
 
@@ -78,20 +74,16 @@ impl StaticMemory {
             }
         }
 
-        if new_pages as usize > WASM_MAX_PAGES {
-            return None;
-        }
-
         unsafe {
             self.memory
                 .protect(
-                    self.current as usize * WASM_PAGE_SIZE..new_pages as usize * WASM_PAGE_SIZE,
+                    self.current.bytes().0..new_pages.bytes().0,
                     sys::Protect::ReadWrite,
                 )
                 .ok()?;
         }
 
-        local.bound = new_pages as usize * WASM_PAGE_SIZE;
+        local.bound = new_pages.bytes().0;
 
         let old_pages = self.current;
 
@@ -101,10 +93,10 @@ impl StaticMemory {
     }
 
     pub fn as_slice(&self) -> &[u8] {
-        unsafe { &self.memory.as_slice()[0..self.current as usize * WASM_PAGE_SIZE] }
+        unsafe { &self.memory.as_slice()[0..self.current.bytes().0] }
     }
 
     pub fn as_slice_mut(&mut self) -> &mut [u8] {
-        unsafe { &mut self.memory.as_slice_mut()[0..self.current as usize * WASM_PAGE_SIZE] }
+        unsafe { &mut self.memory.as_slice_mut()[0..self.current.bytes().0] }
     }
 }

lib/runtime-core/src/table/anyfunc.rs

@@ -1,4 +1,5 @@
 use crate::{
+    error::CreationError,
     instance::Function,
     sig_registry::SigRegistry,
     structures::TypedIndex,
@@ -48,7 +49,10 @@ pub struct AnyfuncTable {
 }
 
 impl AnyfuncTable {
-    pub fn new(desc: TableDescriptor, local: &mut vm::LocalTable) -> Result<Box<Self>, ()> {
+    pub fn new(
+        desc: TableDescriptor,
+        local: &mut vm::LocalTable,
+    ) -> Result<Box<Self>, CreationError> {
         let initial_table_backing_len = match desc.maximum {
             Some(max) => max,
             None => desc.minimum,

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

@@ -1,4 +1,5 @@
 use crate::{
+    error::CreationError,
     export::Export,
     import::IsExport,
     types::{ElementType, TableDescriptor},
@@ -28,29 +29,27 @@ pub struct Table {
 
 impl Table {
     /// Create a new `Table` from a [`TableDescriptor`]
-    /// 
+    ///
     /// [`TableDescriptor`]: struct.TableDescriptor.html
-    /// 
+    ///
     /// Usage:
-    /// 
+    ///
     /// ```
     /// # use wasmer_runtime_core::types::{TableDescriptor, ElementType};
     /// # use wasmer_runtime_core::table::Table;
     /// # use wasmer_runtime_core::error::Result;
-    /// 
     /// # fn create_table() -> Result<()> {
     /// let descriptor = TableDescriptor {
     ///     element: ElementType::Anyfunc,
     ///     minimum: 10,
     ///     maximum: None,
     /// };
-    /// 
+    ///
     /// let table = Table::new(descriptor)?;
-    /// 
     /// # Ok(())
     /// # }
     /// ```
-    pub fn new(desc: TableDescriptor) -> Result<Self, ()> {
+    pub fn new(desc: TableDescriptor) -> Result<Self, CreationError> {
         let mut local = vm::LocalTable {
             base: ptr::null_mut(),
             count: 0,
@@ -67,10 +66,12 @@ impl Table {
         })
     }
 
+    /// Get the `TableDescriptor` used to create this `Table`.
     pub fn descriptor(&self) -> TableDescriptor {
         self.desc
     }
 
+    /// Set the element at index.
     pub fn set(&self, index: u32, element: Element) -> Result<(), ()> {
         match &mut *self.storage.borrow_mut() {
             (TableStorage::Anyfunc(ref mut anyfunc_table), _) => {
@@ -91,15 +92,17 @@ impl Table {
         }
     }
 
-    pub fn current_size(&self) -> u32 {
+    /// The current size of this table.
+    pub fn size(&self) -> u32 {
         match &*self.storage.borrow() {
             (TableStorage::Anyfunc(ref anyfunc_table), _) => anyfunc_table.current_size(),
         }
     }
 
+    /// Grow this table by `delta`.
     pub fn grow(&self, delta: u32) -> Option<u32> {
         if delta == 0 {
-            return Some(self.current_size());
+            return Some(self.size());
         }
 
         match &mut *self.storage.borrow_mut() {
@@ -131,6 +134,9 @@ impl Clone for Table {
 
 impl fmt::Debug for Table {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("Table").field("desc", &self.desc).finish()
+        f.debug_struct("Table")
+            .field("desc", &self.desc)
+            .field("size", &self.size())
+            .finish()
     }
 }

lib/runtime-core/src/types.rs

@@ -1,4 +1,4 @@
-use crate::{memory::MemoryType, module::ModuleInner, structures::TypedIndex};
+use crate::{memory::MemoryType, module::ModuleInner, structures::TypedIndex, units::Pages};
 use std::{borrow::Cow, mem};
 
 /// Represents a WebAssembly type.
@@ -142,7 +142,9 @@ impl TableDescriptor {
         // TODO: We should define implementation limits.
         let imported_max = imported.maximum.unwrap_or(u32::max_value());
         let self_max = self.maximum.unwrap_or(u32::max_value());
-        self.element == imported.element && imported_max <= self_max && self.minimum <= imported.minimum
+        self.element == imported.element
+            && imported_max <= self_max
+            && self.minimum <= imported.minimum
     }
 }
 
@@ -174,9 +176,9 @@ pub struct GlobalInit {
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct MemoryDescriptor {
     /// The minimum number of allowed pages.
-    pub minimum: u32,
+    pub minimum: Pages,
     /// The maximum number of allowed pages.
-    pub maximum: Option<u32>,
+    pub maximum: Option<Pages>,
     /// This memory can be shared between wasm threads.
     pub shared: bool,
 }
@@ -192,10 +194,12 @@ impl MemoryDescriptor {
     }
 
     pub(crate) fn fits_in_imported(&self, imported: MemoryDescriptor) -> bool {
-        let imported_max = imported.maximum.unwrap_or(65_536);
+        let imported_max = imported.maximum.unwrap_or(Pages(65_536));
-        let self_max = self.maximum.unwrap_or(65_536);
+        let self_max = self.maximum.unwrap_or(Pages(65_536));
 
-        self.shared == imported.shared && imported_max <= self_max && self.minimum <= imported.minimum
+        self.shared == imported.shared
+            && imported_max <= self_max
+            && self.minimum <= imported.minimum
     }
 }
 

lib/runtime-core/src/units.rs

@@ -0,0 +1,94 @@
+use std::{
+    fmt,
+    ops::{Add, Sub},
+};
+
+const WASM_PAGE_SIZE: usize = 65_536;
+const WASM_MAX_PAGES: usize = 65_536;
+
+/// Units of WebAssembly pages (as specified to be 65,536 bytes).
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Pages(pub u32);
+
+impl Pages {
+    pub fn checked_add(self, rhs: Pages) -> Option<Pages> {
+        let added = (self.0 as usize) + (rhs.0 as usize);
+        if added <= WASM_MAX_PAGES {
+            Some(Pages(added as u32))
+        } else {
+            None
+        }
+    }
+
+    pub fn bytes(self) -> Bytes {
+        self.into()
+    }
+}
+
+impl fmt::Debug for Pages {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} pages", self.0)
+    }
+}
+
+/// Units of WebAssembly memory in terms of 8-bit bytes.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Bytes(pub usize);
+
+impl fmt::Debug for Bytes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} bytes", self.0)
+    }
+}
+
+impl From<Pages> for Bytes {
+    fn from(pages: Pages) -> Bytes {
+        Bytes((pages.0 as usize) * WASM_PAGE_SIZE)
+    }
+}
+
+impl<T> Sub<T> for Pages
+where
+    T: Into<Pages>,
+{
+    type Output = Pages;
+    fn sub(self, rhs: T) -> Pages {
+        Pages(self.0 - rhs.into().0)
+    }
+}
+
+impl<T> Add<T> for Pages
+where
+    T: Into<Pages>,
+{
+    type Output = Pages;
+    fn add(self, rhs: T) -> Pages {
+        Pages(self.0 + rhs.into().0)
+    }
+}
+
+impl From<Bytes> for Pages {
+    fn from(bytes: Bytes) -> Pages {
+        Pages((bytes.0 / WASM_PAGE_SIZE) as u32)
+    }
+}
+
+impl<T> Sub<T> for Bytes
+where
+    T: Into<Bytes>,
+{
+    type Output = Bytes;
+    fn sub(self, rhs: T) -> Bytes {
+        Bytes(self.0 - rhs.into().0)
+    }
+}
+
+impl<T> Add<T> for Bytes
+where
+    T: Into<Bytes>,
+{
+    type Output = Bytes;
+    fn add(self, rhs: T) -> Bytes {
+        Bytes(self.0 + rhs.into().0)
+    }
+}

lib/runtime-core/src/vmcalls.rs

@@ -4,6 +4,7 @@ use crate::{
     memory::{DynamicMemory, StaticMemory},
     structures::TypedIndex,
     types::{ImportedMemoryIndex, LocalMemoryIndex, LocalTableIndex},
+    units::Pages,
     vm,
 };
 
@@ -13,14 +14,14 @@ use crate::{
 
 pub unsafe extern "C" fn local_static_memory_grow(
     memory_index: LocalMemoryIndex,
-    delta: u32,
+    delta: Pages,
     ctx: &mut vm::Ctx,
 ) -> i32 {
     let local_memory = *ctx.memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut StaticMemory;
 
     if let Some(old) = (*memory).grow(delta, &mut *local_memory) {
-        old as i32
+        old.0 as i32
     } else {
         -1
     }
@@ -29,23 +30,23 @@ pub unsafe extern "C" fn local_static_memory_grow(
 pub unsafe extern "C" fn local_static_memory_size(
     memory_index: LocalMemoryIndex,
     ctx: &vm::Ctx,
-) -> u32 {
+) -> Pages {
     let local_memory = *ctx.memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut StaticMemory;
 
-    (*memory).current()
+    (*memory).size()
 }
 
 pub unsafe extern "C" fn local_dynamic_memory_grow(
     memory_index: LocalMemoryIndex,
-    delta: u32,
+    delta: Pages,
     ctx: &mut vm::Ctx,
 ) -> i32 {
     let local_memory = *ctx.memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut DynamicMemory;
 
     if let Some(old) = (*memory).grow(delta, &mut *local_memory) {
-        old as i32
+        old.0 as i32
     } else {
         -1
     }
@@ -54,11 +55,11 @@ pub unsafe extern "C" fn local_dynamic_memory_grow(
 pub unsafe extern "C" fn local_dynamic_memory_size(
     memory_index: LocalMemoryIndex,
     ctx: &vm::Ctx,
-) -> u32 {
+) -> Pages {
     let local_memory = *ctx.memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut DynamicMemory;
 
-    (*memory).current()
+    (*memory).size()
 }
 
 // +*****************************+
@@ -67,14 +68,14 @@ pub unsafe extern "C" fn local_dynamic_memory_size(
 
 pub unsafe extern "C" fn imported_static_memory_grow(
     import_memory_index: ImportedMemoryIndex,
-    delta: u32,
+    delta: Pages,
     ctx: &mut vm::Ctx,
 ) -> i32 {
     let local_memory = *ctx.imported_memories.add(import_memory_index.index());
     let memory = (*local_memory).memory as *mut StaticMemory;
 
     if let Some(old) = (*memory).grow(delta, &mut *local_memory) {
-        old as i32
+        old.0 as i32
     } else {
         -1
     }
@@ -83,23 +84,23 @@ pub unsafe extern "C" fn imported_static_memory_grow(
 pub unsafe extern "C" fn imported_static_memory_size(
     import_memory_index: ImportedMemoryIndex,
     ctx: &vm::Ctx,
-) -> u32 {
+) -> Pages {
     let local_memory = *ctx.imported_memories.add(import_memory_index.index());
     let memory = (*local_memory).memory as *mut StaticMemory;
 
-    (*memory).current()
+    (*memory).size()
 }
 
 pub unsafe extern "C" fn imported_dynamic_memory_grow(
     memory_index: ImportedMemoryIndex,
-    delta: u32,
+    delta: Pages,
     ctx: &mut vm::Ctx,
 ) -> i32 {
     let local_memory = *ctx.imported_memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut DynamicMemory;
 
     if let Some(old) = (*memory).grow(delta, &mut *local_memory) {
-        old as i32
+        old.0 as i32
     } else {
         -1
     }
@@ -108,11 +109,11 @@ pub unsafe extern "C" fn imported_dynamic_memory_grow(
 pub unsafe extern "C" fn imported_dynamic_memory_size(
     memory_index: ImportedMemoryIndex,
     ctx: &vm::Ctx,
-) -> u32 {
+) -> Pages {
     let local_memory = *ctx.imported_memories.add(memory_index.index());
     let memory = (*local_memory).memory as *mut DynamicMemory;
 
-    (*memory).current()
+    (*memory).size()
 }
 
 // +*****************************+

lib/runtime/src/lib.rs

@@ -88,6 +88,7 @@ pub use wasmer_runtime_core::error;
 pub use wasmer_runtime_core::{func, imports};
 
 pub mod wasm {
+    //! Various types exposed by the Wasmer Runtime.
     pub use wasmer_runtime_core::global::Global;
     pub use wasmer_runtime_core::instance::Function;
     pub use wasmer_runtime_core::memory::Memory;
@@ -95,6 +96,12 @@ pub mod wasm {
     pub use wasmer_runtime_core::types::{FuncSig, MemoryDescriptor, TableDescriptor, Type, Value};
 }
 
+pub mod units {
+    //! Various unit types.
+
+    pub use wasmer_runtime_core::units::{Bytes, Pages};
+}
+
 /// Compile WebAssembly binary code into a [`Module`].
 /// This function is useful if it is necessary to
 /// compile a module before it can be instantiated