Make the calls to wasm's memory.grow and memory.size indirect (#194)

* Make the calls to wasm's memory.grow and memory.size indirect

wasmtime-runtime/src/instance.rs

@@ -11,9 +11,9 @@ use crate::signalhandlers::{wasmtime_init_eager, wasmtime_init_finish};
 use crate::table::Table;
 use crate::traphandlers::wasmtime_call;
 use crate::vmcontext::{
-    VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport, VMGlobalDefinition,
-    VMGlobalImport, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex, VMTableDefinition,
-    VMTableImport,
+    VMBuiltinFunctionsArray, VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport,
+    VMGlobalDefinition, VMGlobalImport, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex,
+    VMTableDefinition, VMTableImport,
 };
 use core::any::Any;
 use core::borrow::Borrow;
@@ -360,6 +360,15 @@ impl Instance {
         }
     }
 
+    /// Return a pointer to the `VMBuiltinFunctionsArray`.
+    fn builtin_functions_ptr(&mut self) -> *mut VMBuiltinFunctionsArray {
+        unsafe {
+            (&mut self.vmctx as *mut VMContext as *mut u8)
+                .add(usize::try_from(self.offsets.vmctx_builtin_functions_begin()).unwrap())
+                as *mut VMBuiltinFunctionsArray
+        }
+    }
+
     /// Return a reference to the vmctx used by compiled wasm code.
     pub fn vmctx(&self) -> &VMContext {
         &self.vmctx
@@ -723,6 +732,10 @@ impl InstanceHandle {
                 instance.globals_ptr() as *mut VMGlobalDefinition,
                 vmctx_globals.len(),
             );
+            ptr::write(
+                instance.builtin_functions_ptr() as *mut VMBuiltinFunctionsArray,
+                VMBuiltinFunctionsArray::initialized(),
+            );
         }
 
         // Check initializer bounds before initializing anything.

wasmtime-runtime/src/vmcontext.rs

@@ -4,6 +4,7 @@
 use crate::instance::Instance;
 use core::any::Any;
 use core::{ptr, u32};
+use wasmtime_environ::BuiltinFunctionIndex;
 
 /// An imported function.
 #[derive(Debug, Copy, Clone)]
@@ -472,6 +473,33 @@ impl Default for VMCallerCheckedAnyfunc {
     }
 }
 
+/// An array that stores addresses of builtin functions. We translate code
+/// to use indirect calls. This way, we don't have to patch the code.
+#[repr(C)]
+pub struct VMBuiltinFunctionsArray {
+    ptrs: [usize; Self::len()],
+}
+
+impl VMBuiltinFunctionsArray {
+    pub const fn len() -> usize {
+        BuiltinFunctionIndex::builtin_functions_total_number() as usize
+    }
+
+    pub fn initialized() -> Self {
+        use crate::libcalls::*;
+        let mut ptrs = [0; Self::len()];
+        ptrs[BuiltinFunctionIndex::get_memory32_grow_index().index() as usize] =
+            wasmtime_memory32_grow as usize;
+        ptrs[BuiltinFunctionIndex::get_imported_memory32_grow_index().index() as usize] =
+            wasmtime_imported_memory32_grow as usize;
+        ptrs[BuiltinFunctionIndex::get_memory32_size_index().index() as usize] =
+            wasmtime_memory32_size as usize;
+        ptrs[BuiltinFunctionIndex::get_imported_memory32_size_index().index() as usize] =
+            wasmtime_imported_memory32_size as usize;
+        Self { ptrs }
+    }
+}
+
 /// The VM "context", which is pointed to by the `vmctx` arg in Cranelift.
 /// This has information about globals, memories, tables, and other runtime
 /// state associated with the current instance.