Add a FuncEnvironment::make_indirect_sig() callback.

The function environment is now expected to keep track of the function
signatures in the module, and it is asked to generate Cretonne
signatures to be used for indirect calls.

The combination of make_indirect_sig() and translate_call_indirect()
callbacks allow the runtime to insert additional function arguments for
indirect calls such as vmctx pointers and CFI-style signature identifiers.

lib/wasm/src/runtime/spec.rs

@@ -2,8 +2,8 @@
 //! trait `WasmRuntime`.
 use cton_frontend::FunctionBuilder;
 use cretonne::ir::{self, Value, SigRef};
-use translation_utils::{Local, FunctionIndex, TableIndex, GlobalIndex, MemoryIndex, Global, Table,
-                        Memory};
+use translation_utils::{Local, SignatureIndex, FunctionIndex, TableIndex, GlobalIndex,
+                        MemoryIndex, Global, Table, Memory};
 
 /// The value of a WebAssembly global variable.
 #[derive(Clone, Copy)]
@@ -40,12 +40,26 @@ pub trait FuncEnvironment {
     ///
     /// The index space covers both imported and locally declared memories.
     fn make_heap(&self, func: &mut ir::Function, index: MemoryIndex) -> ir::Heap;
+
+    /// Set up a signature definition in the preamble of `func` that can be used for an indirect
+    /// call with signature `index`.
+    ///
+    /// The signature may contain additional arguments needed for an indirect call, but the
+    /// arguments marked as `ArgumentPurpose::Normal` must correspond to the WebAssembly signature
+    /// arguments.
+    ///
+    /// The signature will only be used for indirect calls, even if the module has direct function
+    /// calls with the same WebAssembly type.
+    fn make_indirect_sig(&self, func: &mut ir::Function, index: SignatureIndex) -> ir::SigRef;
 }
 
 /// An object satisfyng the `WasmRuntime` trait can be passed as argument to the
 /// [`translate_module`](fn.translate_module.html) function. These methods should not be called
 /// by the user, they are only for the `wasm2cretonne` internal use.
 pub trait WasmRuntime: FuncEnvironment {
+    /// Declares a function signature to the runtime.
+    fn declare_signature(&mut self, sig: &ir::Signature);
+
     /// Declares a global to the runtime.
     fn declare_global(&mut self, global: Global);
     /// Declares a table to the runtime.