Add preliminary support for throwing and catching uncatchable exceptions.

Additional info:
- WebAssembly "traps" are uncatchable, but are still caught by the trampoline caller.

lib/llvm-backend/cpp/object_loader.hh

@@ -1,6 +1,9 @@
 #include <cstddef>
 #include <cstdint>
 #include <llvm/ExecutionEngine/RuntimeDyld.h>
+#include <iostream>
+#include <sstream>
+#include <exception>
 
 typedef enum {
     PROTECT_NONE,
@@ -24,6 +27,8 @@ typedef uintptr_t (*lookup_vm_symbol_t)(const char* name_ptr, size_t length);
 typedef void (*fde_visitor_t)(uint8_t *fde);
 typedef result_t (*visit_fde_t)(uint8_t *fde, size_t size, fde_visitor_t visitor);
 
+typedef void (*trampoline_t)(void*, void*, void*, void*);
+
 typedef struct {
     /* Memory management. */
     alloc_memory_t alloc_memory;
@@ -35,6 +40,59 @@ typedef struct {
     visit_fde_t visit_fde;
 } callbacks_t;
 
+class WasmException {
+public:
+    virtual std::string description() const noexcept = 0;
+};
+
+struct UncatchableException : WasmException {
+public:
+    enum class Type {
+        Unreachable,
+        IncorrectCallIndirectSignature,
+        Unknown,
+    } type;
+
+    UncatchableException(Type type) : type(type) {}
+
+    virtual std::string description() const noexcept override {
+        std::ostringstream ss;
+        ss
+            << "Uncatchable exception:" << '\n'
+            << " - type: " << type << '\n';
+        
+        return ss.str();
+    }
+
+private:
+    friend std::ostream& operator<<(std::ostream& out, const Type& ty) {
+        switch (ty) {
+            case Type::Unreachable:
+                out << "unreachable";
+                break;
+            case Type::IncorrectCallIndirectSignature:
+                out << "incorrect call_indirect signature";
+                break;
+            case Type::Unknown:
+                out << "unknown";
+                break;
+        }
+        return out;
+    }
+};
+
+struct CatchableException : WasmException {
+public:
+    CatchableException(uint32_t type_id, uint32_t value_num) : type_id(type_id), value_num(value_num) {}
+
+    virtual std::string description() const noexcept override {
+        return "catchable exception";
+    }
+
+    uint32_t type_id, value_num;
+    uint64_t values[];
+};
+
 class WasmModule {
 public:
     WasmModule(
@@ -57,10 +115,27 @@ extern "C" {
         return RESULT_OK;
     }
 
+    void throw_unreachable_exception() {
+        throw UncatchableException(UncatchableException::Type::Unreachable);
+    }
+    void throw_incorrect_call_indirect_signature() {
+        throw UncatchableException(UncatchableException::Type::IncorrectCallIndirectSignature);
+    }
+
     void module_delete(WasmModule* module) {
         delete module;
     }
 
+    void invoke_trampoline(trampoline_t trampoline, void* ctx, void* func, void* params, void* results) {
+        try {
+            trampoline(ctx, func, params, results);
+        } catch(const WasmException& e) {
+            std::cout << e.description() << std::endl;
+        } catch (...) {
+            std::cout << "unknown exception" << std::endl;
+        }
+    }
+
     void* get_func_symbol(WasmModule* module, const char* name) {
         return module->get_func(llvm::StringRef(name));
     }

lib/llvm-backend/src/backend.rs

@@ -71,6 +71,16 @@ extern "C" {
     ) -> LLVMResult;
     fn module_delete(module: *mut LLVMModule);
     fn get_func_symbol(module: *mut LLVMModule, name: *const c_char) -> *const vm::Func;
+    fn throw_unreachable_exception();
+    fn throw_incorrect_call_indirect_signature();
+    // invoke_trampoline(trampoline_t trampoline, void* ctx, void* func, void* params, void* results)
+    fn invoke_trampoline(
+        trampoline: unsafe extern "C" fn(*mut vm::Ctx, *const vm::Func, *const u64, *mut u64),
+        vmctx_ptr: *mut vm::Ctx,
+        func_ptr: *const vm::Func,
+        params: *const u64,
+        results: *mut u64,
+    );
 }
 
 fn get_callbacks() -> Callbacks {
@@ -162,6 +172,11 @@ fn get_callbacks() -> Callbacks {
             fn_name!("vm.memory.size.dynamic.local") => vmcalls::local_dynamic_memory_size as _,
             fn_name!("vm.memory.grow.static.local") => vmcalls::local_static_memory_grow as _,
             fn_name!("vm.memory.size.static.local") => vmcalls::local_static_memory_size as _,
+
+            fn_name!("vm.exception.throw.unreachable") => throw_unreachable_exception as _,
+            fn_name!("vm.exception.throw.incorrect-call_indirect_signature") => {
+                throw_incorrect_call_indirect_signature as _
+            }
             _ => ptr::null(),
         }
     }
@@ -343,7 +358,8 @@ impl ProtectedCaller for LLVMProtectedCaller {
 
         // Here we go.
         unsafe {
-            trampoline(
+            invoke_trampoline(
+                trampoline,
                 vmctx_ptr,
                 func_ptr,
                 param_vec.as_ptr(),

lib/llvm-backend/src/code.rs

@@ -539,6 +539,9 @@ fn parse_function(
                 // Emit an unreachable instruction.
                 // If llvm cannot prove that this is never touched,
                 // it will emit a `ud2` instruction on x86_64 arches.
+
+                builder.build_call(intrinsics.throw_unreachable, &[], "throw");
+
                 ctx.build_trap();
                 builder.build_unreachable();
 
@@ -731,13 +734,12 @@ fn parse_function(
                     )
                 };
 
-                // let sigindices_equal = builder.build_int_compare(
-                //     IntPredicate::EQ,
-                //     expected_dynamic_sigindex,
-                //     found_dynamic_sigindex,
-                //     "sigindices_equal",
-                // );
-                let sigindices_equal = intrinsics.i1_ty.const_int(1, false);
+                let sigindices_equal = builder.build_int_compare(
+                    IntPredicate::EQ,
+                    expected_dynamic_sigindex,
+                    found_dynamic_sigindex,
+                    "sigindices_equal",
+                );
 
                 // Tell llvm that `expected_dynamic_sigindex` should equal `found_dynamic_sigindex`.
                 let sigindices_equal = builder
@@ -764,7 +766,11 @@ fn parse_function(
                 );
 
                 builder.position_at_end(&sigindices_notequal_block);
-                ctx.build_trap();
+                builder.build_call(
+                    intrinsics.throw_incorrect_call_indirect_signature,
+                    &[],
+                    "throw",
+                );
                 builder.build_unreachable();
                 builder.position_at_end(&continue_block);
 

lib/llvm-backend/src/intrinsics.rs

@@ -105,6 +105,9 @@ pub struct Intrinsics {
     pub memory_size_static_import: FunctionValue,
     pub memory_size_shared_import: FunctionValue,
 
+    pub throw_unreachable: FunctionValue,
+    pub throw_incorrect_call_indirect_signature: FunctionValue,
+
     ctx_ty: StructType,
     pub ctx_ptr_ty: PointerType,
 }
@@ -344,7 +347,16 @@ impl Intrinsics {
                 ret_i32_take_ctx_i32,
                 None,
             ),
-
+            throw_unreachable: module.add_function(
+                "vm.exception.throw.unreachable",
+                void_ty.fn_type(&[], false),
+                None,
+            ),
+            throw_incorrect_call_indirect_signature: module.add_function(
+                "vm.exception.throw.incorrect-call_indirect_signature",
+                void_ty.fn_type(&[], false),
+                None,
+            ),
             ctx_ty,
             ctx_ptr_ty,
         }

lib/runtime/examples/call.rs

@@ -6,7 +6,7 @@ static WAT: &'static str = r#"
     (module
       (type (;0;) (func (param i32) (result i32)))
       (func (;0;) (type 0) (param i32) (result i32)
-        i32.const 42)
+        unreachable)
       (export "select_trap_l" (func 0))
     )
 "#;