Remove use of offset_of! from wasmtime-environ.

wasmtime-environ is meant to support cross compilation, so it shouldn't
have dependencies on target layout of structs. This moves the layout
back into wasmtime-execute, and adds a system of asserts for checking
that wasmtime-environ's offsets stay in sync.

lib/environ/Cargo.toml

@@ -13,7 +13,7 @@ readme = "README.md"
 cranelift-codegen = { git = "https://github.com/sunfishcode/cranelift.git", branch = "guard-offset" }
 cranelift-entity = { git = "https://github.com/sunfishcode/cranelift.git", branch = "guard-offset" }
 cranelift-wasm = { git = "https://github.com/sunfishcode/cranelift.git", branch = "guard-offset" }
-memoffset = "0.2.1"
+cast = { version = "0.2.2", default-features = false }
 
 [features]
 default = ["std"]

lib/environ/src/environ.rs

@@ -15,17 +15,15 @@ use module::{
     DataInitializer, Export, LazyContents, MemoryPlan, MemoryStyle, Module, TableElements,
 };
 use std::clone::Clone;
-use std::mem;
 use std::string::String;
 use std::vec::Vec;
 use tunables::Tunables;
-use vmcontext;
+use vmoffsets::VMOffsets;
 use WASM_PAGE_SIZE;
 
 /// Compute a `ir::ExternalName` for a given wasm function index.
 pub fn get_func_name(func_index: FuncIndex) -> ir::ExternalName {
-    debug_assert!(FuncIndex::new(func_index.index() as u32 as usize) == func_index);
-    ir::ExternalName::user(0, func_index.index() as u32)
+    ir::ExternalName::user(0, func_index.as_u32())
 }
 
 /// Object containing the standalone environment information. To be passed after creation as
@@ -104,6 +102,9 @@ pub struct FuncEnvironment<'module_environment> {
 
     /// The external function declaration for implementing wasm's `grow_memory`.
     grow_memory_extfunc: Option<FuncRef>,
+
+    /// Offsets to struct fields accessed by JIT code.
+    offsets: VMOffsets,
 }
 
 impl<'module_environment> FuncEnvironment<'module_environment> {
@@ -120,6 +121,7 @@ impl<'module_environment> FuncEnvironment<'module_environment> {
             globals_base: None,
             current_memory_extfunc: None,
             grow_memory_extfunc: None,
+            offsets: VMOffsets::new(isa.frontend_config().pointer_bytes()),
         }
     }
 
@@ -149,10 +151,6 @@ impl<'module_environment> FuncEnvironment<'module_environment> {
 impl<'data, 'module> cranelift_wasm::ModuleEnvironment<'data>
     for ModuleEnvironment<'data, 'module>
 {
-    fn get_func_name(&self, func_index: FuncIndex) -> ir::ExternalName {
-        get_func_name(func_index)
-    }
-
     fn target_config(&self) -> isa::TargetFrontendConfig {
         self.isa.frontend_config()
     }
@@ -302,19 +300,16 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
         let globals_base = self.globals_base.unwrap_or_else(|| {
             let new_base = func.create_global_value(ir::GlobalValueData::Load {
                 base: vmctx,
-                offset: Offset32::new(offset_of!(vmcontext::VMContext, globals) as i32),
+                offset: Offset32::new(i32::from(self.offsets.vmctx_globals())),
                 global_type: self.pointer_type(),
                 readonly: true,
             });
             self.globals_base = Some(new_base);
             new_base
         });
-        // For now, give each global gets a pointer-sized region of
-        // storage, regardless of its type.
-        let offset = index.index() * mem::size_of::<*mut u8>();
         let gv = func.create_global_value(ir::GlobalValueData::IAddImm {
             base: globals_base,
-            offset: Imm64::new(offset as i64),
+            offset: Imm64::new(i64::from(self.offsets.index_vmglobal(index.as_u32()))),
             global_type: self.pointer_type(),
         });
         GlobalVariable::Memory {
@@ -328,16 +323,13 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
         let memories_base = self.memories_base.unwrap_or_else(|| {
             let new_base = func.create_global_value(ir::GlobalValueData::Load {
                 base: vmctx,
-                offset: Offset32::new(offset_of!(vmcontext::VMContext, memories) as i32),
+                offset: Offset32::new(i32::from(self.offsets.vmctx_memories())),
                 global_type: self.pointer_type(),
                 readonly: true,
             });
             self.memories_base = Some(new_base);
             new_base
         });
-        let offset = index.index() * mem::size_of::<vmcontext::VMMemory>();
-        let offset32 = offset as i32;
-        debug_assert_eq!(offset32 as usize, offset);
         // If we have a declared maximum, we can make this a "static" heap, which is
         // allocated up front and never moved.
         let (offset_guard_size, heap_style, readonly_base) = match self.module.memory_plans[index] {
@@ -349,7 +341,7 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
                 let heap_bound = func.create_global_value(ir::GlobalValueData::Load {
                     base: memories_base,
                     offset: Offset32::new(
-                        offset32 + offset_of!(vmcontext::VMMemory, current_length) as i32,
+                        self.offsets.index_vmmemory_current_length(index.as_u32()),
                     ),
                     global_type: I32,
                     readonly: false,
@@ -377,7 +369,7 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
 
         let heap_base = func.create_global_value(ir::GlobalValueData::Load {
             base: memories_base,
-            offset: Offset32::new(offset32 + offset_of!(vmcontext::VMMemory, base) as i32),
+            offset: Offset32::new(self.offsets.index_vmmemory_base(index.as_u32())),
             global_type: self.pointer_type(),
             readonly: readonly_base,
         });
@@ -395,27 +387,22 @@ impl<'module_environment> cranelift_wasm::FuncEnvironment for FuncEnvironment<'m
         let tables_base = self.tables_base.unwrap_or_else(|| {
             let new_base = func.create_global_value(ir::GlobalValueData::Load {
                 base: vmctx,
-                offset: Offset32::new(offset_of!(vmcontext::VMContext, tables) as i32),
+                offset: Offset32::new(i32::from(self.offsets.vmctx_tables())),
                 global_type: self.pointer_type(),
                 readonly: true,
             });
             self.tables_base = Some(new_base);
             new_base
         });
-        let offset = index.index() * mem::size_of::<vmcontext::VMTable>();
-        let offset32 = offset as i32;
-        debug_assert_eq!(offset32 as usize, offset);
         let base_gv = func.create_global_value(ir::GlobalValueData::Load {
             base: tables_base,
-            offset: Offset32::new(offset32 + offset_of!(vmcontext::VMTable, base) as i32),
+            offset: Offset32::new(self.offsets.index_vmtable_base(index.as_u32())),
             global_type: self.pointer_type(),
             readonly: false,
         });
         let bound_gv = func.create_global_value(ir::GlobalValueData::Load {
             base: tables_base,
-            offset: Offset32::new(
-                offset32 + offset_of!(vmcontext::VMTable, current_num_elements) as i32,
-            ),
+            offset: Offset32::new(self.offsets.index_vmtable_current_elements(index.as_u32())),
             global_type: I32,
             readonly: false,
         });

lib/environ/src/lib.rs

@@ -33,8 +33,6 @@
 extern crate cranelift_codegen;
 extern crate cranelift_entity;
 extern crate cranelift_wasm;
-#[macro_use]
-extern crate memoffset;
 #[cfg(not(feature = "std"))]
 #[macro_use]
 extern crate alloc;
@@ -43,7 +41,7 @@ mod compilation;
 mod environ;
 mod module;
 mod tunables;
-mod vmcontext;
+mod vmoffsets;
 
 pub use compilation::{
     compile_module, Compilation, RelocSink, Relocation, RelocationTarget, Relocations,

lib/environ/src/vmcontext.rs

@@ -1,33 +0,0 @@
-/// The main fields a JIT needs to access to utilize a WebAssembly linear,
-/// memory, namely the start address and the size in bytes.
-#[repr(C, packed)]
-pub struct VMMemory {
-    pub base: *mut u8,
-    pub current_length: usize,
-}
-
-/// The main fields a JIT needs to access to utilize a WebAssembly table,
-/// namely the start address and the number of elements.
-#[repr(C, packed)]
-pub struct VMTable {
-    pub base: *mut u8,
-    pub current_num_elements: usize,
-}
-
-/// The VM "context", which is pointed to by the `vmctx` arg in Cranelift.
-/// This has pointers to the globals, memories, tables, and other runtime
-/// state associated with the current instance.
-#[repr(C, packed)]
-pub struct VMContext {
-    /// A pointer to an array of globals.
-    pub globals: *mut u8,
-    /// A pointer to an array of `VMMemory` instances, indexed by
-    /// WebAssembly memory index.
-    pub memories: *mut VMMemory,
-    /// A pointer to an array of `VMTable` instances, indexed by
-    /// WebAssembly table index.
-    pub tables: *mut VMTable,
-    /// A pointer to extra runtime state that isn't directly accessed
-    /// from JIT code.
-    pub instance: *mut u8,
-}

lib/environ/src/vmoffsets.rs

@@ -0,0 +1,145 @@
+/// This class computes offsets to fields within `VMContext` and other
+/// related structs that JIT code accesses directly.
+pub struct VMOffsets {
+    pointer_size: u8,
+}
+
+impl VMOffsets {
+    /// Return a new `VMOffsets` instance, for a given pointer size.
+    pub fn new(pointer_size: u8) -> Self {
+        Self { pointer_size }
+    }
+}
+
+/// Offsets for `wasmtime_execute::VMMemory`.
+impl VMOffsets {
+    /// The offset of the `base` field.
+    pub fn vmmemory_base(&self) -> u8 {
+        0 * self.pointer_size
+    }
+
+    /// The offset of the `current_length` field.
+    pub fn vmmemory_current_length(&self) -> u8 {
+        1 * self.pointer_size
+    }
+
+    /// Return the size of `VMMemory`.
+    pub fn size_of_vmmemory(&self) -> u8 {
+        2 * self.pointer_size
+    }
+}
+
+/// Offsets for `wasmtime_execute::VMGlobal`.
+impl VMOffsets {
+    /// Return the size of `VMGlobal`.
+    pub fn size_of_vmglobal(&self) -> u8 {
+        8
+    }
+}
+
+/// Offsets for `wasmtime_execute::VMTable`.
+impl VMOffsets {
+    /// The offset of the `base` field.
+    pub fn vmtable_base(&self) -> u8 {
+        0 * self.pointer_size
+    }
+
+    /// The offset of the `current_elements` field.
+    pub fn vmtable_current_elements(&self) -> u8 {
+        1 * self.pointer_size
+    }
+
+    /// Return the size of `VMTable`.
+    pub fn size_of_vmtable(&self) -> u8 {
+        2 * self.pointer_size
+    }
+}
+
+/// Offsets for `wasmtime_execute::VMContext`.
+impl VMOffsets {
+    /// The offset of the `memories` field.
+    pub fn vmctx_memories(&self) -> u8 {
+        0 * self.pointer_size
+    }
+
+    /// The offset of the `globals` field.
+    pub fn vmctx_globals(&self) -> u8 {
+        1 * self.pointer_size
+    }
+
+    /// The offset of the `tables` field.
+    pub fn vmctx_tables(&self) -> u8 {
+        2 * self.pointer_size
+    }
+
+    /// The offset of the `instance` field.
+    #[allow(dead_code)]
+    pub fn vmctx_instance(&self) -> u8 {
+        3 * self.pointer_size
+    }
+
+    /// Return the size of `VMContext`.
+    #[allow(dead_code)]
+    pub fn size_of_vmctx(&self) -> u8 {
+        4 * self.pointer_size
+    }
+
+    /// Return the offset from the `memories` pointer to `VMMemory` index `index`.
+    pub fn index_vmmemory(&self, index: u32) -> i32 {
+        cast::i32(
+            index
+                .checked_mul(u32::from(self.size_of_vmmemory()))
+                .unwrap(),
+        ).unwrap()
+    }
+
+    /// Return the offset from the `globals` pointer to `VMGlobal` index `index`.
+    pub fn index_vmglobal(&self, index: u32) -> i32 {
+        cast::i32(
+            index
+                .checked_mul(u32::from(self.size_of_vmglobal()))
+                .unwrap(),
+        ).unwrap()
+    }
+
+    /// Return the offset from the `tables` pointer to `VMTable` index `index`.
+    pub fn index_vmtable(&self, index: u32) -> i32 {
+        cast::i32(
+            index
+                .checked_mul(u32::from(self.size_of_vmtable()))
+                .unwrap(),
+        ).unwrap()
+    }
+
+    /// Return the offset from the `memories` pointer to the `base` field in
+    /// `VMMemory` index `index`.
+    pub fn index_vmmemory_base(&self, index: u32) -> i32 {
+        self.index_vmmemory(index)
+            .checked_add(i32::from(self.vmmemory_base()))
+            .unwrap()
+    }
+
+    /// Return the offset from the `memories` pointer to the `current_length` field in
+    /// `VMMemory` index `index`.
+    pub fn index_vmmemory_current_length(&self, index: u32) -> i32 {
+        self.index_vmmemory(index)
+            .checked_add(i32::from(self.vmmemory_current_length()))
+            .unwrap()
+    }
+
+    /// Return the offset from the `tables` pointer to the `base` field in
+    /// `VMTable` index `index`.
+    pub fn index_vmtable_base(&self, index: u32) -> i32 {
+        self.index_vmtable(index)
+            .checked_add(i32::from(self.vmtable_base()))
+            .unwrap()
+    }
+
+    /// Return the offset from the `tables` pointer to the `current_elements` field in
+    /// `VMTable` index `index`.
+    pub fn index_vmtable_current_elements(&self, index: u32) -> i32 {
+        self.index_vmtable(index)
+            .checked_add(i32::from(self.vmtable_current_elements()))
+            .unwrap()
+    }
+}

lib/execute/Cargo.toml

@@ -19,12 +19,16 @@ region = "1.0.0"
 lazy_static = "1.2.0"
 libc = { version = "0.2.44", default-features = false }
 errno = "0.2.4"
+cast = { version = "0.2.2", default-features = false }
 
 [build-dependencies]
 cmake = "0.1.35"
 bindgen = "0.44.0"
 regex = "1.0.6"
 
+[dev-dependencies]
+memoffset = "0.2.1"
+
 [features]
 default = ["std"]
 std = ["cranelift-codegen/std", "cranelift-wasm/std"]

lib/execute/src/execute.rs

@@ -68,6 +68,7 @@ fn relocate<F>(
 
             let body = &mut compilation.functions[i];
             match r.reloc {
+                #[cfg(target_pointer_width = "64")]
                 Reloc::Abs8 => unsafe {
                     let reloc_address = body.as_mut_ptr().add(r.offset as usize) as usize;
                     let reloc_addend = r.addend as isize;
@@ -76,6 +77,7 @@ fn relocate<F>(
                         .unwrap();
                     write_unaligned(reloc_address as *mut u64, reloc_abs);
                 },
+                #[cfg(target_pointer_width = "32")]
                 Reloc::X86PCRel4 => unsafe {
                     let reloc_address = body.as_mut_ptr().add(r.offset as usize) as usize;
                     let reloc_addend = r.addend as isize;

lib/execute/src/lib.rs

@@ -40,6 +40,10 @@ extern crate alloc;
 #[macro_use]
 extern crate lazy_static;
 extern crate libc;
+#[cfg(test)]
+#[macro_use]
+extern crate memoffset;
+extern crate cast;
 
 mod code;
 mod execute;

lib/execute/src/memory.rs

@@ -1,5 +1,6 @@
 //! Memory management for linear memory.
 
+use cast;
 use mmap::Mmap;
 use region;
 use std::fmt;
@@ -69,8 +70,7 @@ impl LinearMemory {
     pub fn current_size(&self) -> u32 {
         assert_eq!(self.mmap.len() % WASM_PAGE_SIZE as usize, 0);
         let num_pages = self.mmap.len() / WASM_PAGE_SIZE as usize;
-        assert_eq!(num_pages as u32 as usize, num_pages);
-        num_pages as u32
+        cast::u32(num_pages).unwrap()
     }
 
     /// Grow memory by the specified amount of pages.

lib/execute/src/vmcontext.rs

@@ -0,0 +1,182 @@
+//! This file declares `VMContext` and several related structs which contain
+//! fields that JIT code accesses directly.
+
+use std::ptr::{size_of, align_of};
+
+/// The main fields a JIT needs to access to utilize a WebAssembly linear,
+/// memory, namely the start address and the size in bytes.
+#[repr(C, packed)]
+pub struct VMMemory {
+    pub base: *mut u8,
+    pub current_length: usize,
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+#[cfg(test)]
+mod test {
+    use wasmtime_environ::VMOffsets;
+
+    #[test]
+    fn check_vmmemory_offsets() {
+        let offsets = VMOffsets::new(size_of<*mut u8>());
+        assert_eq!(size_of<VMMemory>(), offsets.size_of_vmmemory());
+        assert_eq!(offset_of!(VMMemory, base), offsets.vmmemory_base());
+        assert_eq!(offset_of!(VMMemory, current_length), offsets.vmmemory_current_length());
+    }
+}
+
+impl VMMemory {
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.base, self.current_length) }
+    }
+
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        unsafe { slice::from_raw_parts_mut(self.base, self.current_length) }
+    }
+
+    pub fn as_ptr(&self) -> *const u8 {
+        self.base
+    }
+
+    pub fn as_mut_ptr(&mut self) -> *mut u8 {
+        self.base
+    }
+
+    pub fn len(&self) -> usize {
+        self.current_length
+    }
+}
+
+#[repr(C, packed, align(8))]
+pub struct VMGlobal {
+    pub storage: [u8; 8],
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+/// The storage for a WebAssembly global.
+#[cfg(test)]
+mod test {
+    use wasmtime_environ::VMOffsets;
+
+    #[test]
+    fn check_vmglobal_alignment() {
+        assert!(align_of<VMGlobal>() <= align_of<i32>());
+        assert!(align_of<VMGlobal>() >= align_of<i64>());
+        assert!(align_of<VMGlobal>() >= align_of<f32>());
+        assert!(align_of<VMGlobal>() >= align_of<f64>());
+    }
+
+    #[test]
+    fn check_vmglobal_offsets() {
+        let offsets = VMOffsets::new(size_of<*mut u8>());
+        assert_eq!(size_of<VMGlobal>(), offsets.size_of_vmglobal());
+    }
+}
+
+/// The main fields a JIT needs to access to utilize a WebAssembly table,
+/// namely the start address and the number of elements.
+#[repr(C, packed)]
+pub struct VMTableStorage {
+    pub base: *mut u8,
+    pub current_elements: usize,
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+#[cfg(test)]
+mod test {
+    use wasmtime_environ::VMOffsets;
+
+    #[test]
+    fn check_vmtable_offsets() {
+        let offsets = VMOffsets::new(size_of<*mut u8>());
+        assert_eq!(size_of<VMTableStorage>(), offsets.size_of_vmtable());
+        assert_eq!(offset_of!(VMTableStorage, base), offsets.vmtable_base());
+        assert_eq!(offset_of!(VMTableStorage, current_elements), offsets.vmtable_current_elements());
+    }
+}
+
+impl VMTableStorage {
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.base, self.current_length) }
+    }
+
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        unsafe { slice::from_raw_parts_mut(self.base, self.current_length) }
+    }
+
+    pub fn as_ptr(&self) -> *const u8 {
+        self.base
+    }
+
+    pub fn as_mut_ptr(&mut self) -> *mut u8 {
+        self.base
+    }
+
+    pub fn len(&self) -> usize {
+        self.current_length
+    }
+}
+
+/// The VM "context", which is pointed to by the `vmctx` arg in Cranelift.
+/// This has pointers to the globals, memories, tables, and other runtime
+/// state associated with the current instance.
+#[repr(C, packed)]
+pub struct VMContext {
+    /// A pointer to an array of `VMMemory` instances, indexed by
+    /// WebAssembly memory index.
+    pub memories: *mut VMMemory,
+    /// A pointer to an array of globals.
+    pub globals: *mut u8,
+    /// A pointer to an array of `VMTableStorage` instances, indexed by
+    /// WebAssembly table index.
+    pub tables: *mut VMTableStorage,
+    /// A pointer to extra runtime state that isn't directly accessed
+    /// from JIT code.
+    pub instance: *mut u8,
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+#[cfg(test)]
+mod test {
+    use wasmtime_environ::VMOffsets;
+
+    #[test]
+    fn check_vmctx_offsets() {
+        let offsets = VMOffsets::new(size_of<*mut u8>());
+        assert_eq!(size_of<VMContext>(), offsets.size_of_vmctx());
+        assert_eq!(offset_of!(VMContext, globals), offsets.vmctx_globals());
+        assert_eq!(offset_of!(VMContext, memories), offsets.vmctx_memories());
+        assert_eq!(offset_of!(VMContext, tables), offsets.vmctx_tables());
+        assert_eq!(offset_of!(VMContext, instance), offsets.vmctx_instance());
+    }
+}
+
+impl VMContext {
+    unsafe pub fn global_storage(&mut self, index: usize) -> *mut u8 {
+        globals.add(index * global_size)
+    }
+
+    unsafe pub fn global_i32(&mut self, index: usize) -> &mut i32 {
+        self.global_storage(index) as &mut i32
+    }
+
+    unsafe pub fn global_i64(&mut self, index: usize) -> &mut i64 {
+        self.global_storage(index) as &mut i64
+    }
+
+    unsafe pub fn global_f32(&mut self, index: usize) -> &mut f32 {
+        self.global_storage(index) as &mut f32
+    }
+
+    unsafe pub fn global_f64(&mut self, index: usize) -> &mut f64 {
+        self.global_storage(index) as &mut f64
+    }
+
+    unsafe pub fn memory(&mut self, index: usize) -> &mut VMMemory {
+        memories.add(index) as &mut VMMemory
+    }
+
+    unsafe pub fn table(&mut self, index: usize) -> &mut VMTableStorage {
+        tables.add(index) as &mut VMTableStorage
+    }
+}