Implement InternalEvent::Breakpoint in the llvm backend.

lib/llvm-backend/cpp/object_loader.hh

@@ -1,9 +1,10 @@
 #include <cstddef>
 #include <cstdint>
-#include <llvm/ExecutionEngine/RuntimeDyld.h>
+#include <exception>
 #include <iostream>
 #include <sstream>
-#include <exception>
+
+#include <llvm/ExecutionEngine/RuntimeDyld.h>
 
 typedef enum
 {
@@ -77,6 +78,19 @@ struct UserException : UncatchableException
     box_any_t error_data;
 };
 
+struct BreakpointException : UncatchableException
+{
+  public:
+    BreakpointException(uintptr_t callback) : callback(callback) {}
+
+    virtual std::string description() const noexcept override
+    {
+        return "breakpoint exception";
+    }
+
+    uintptr_t callback;
+};
+
 struct WasmTrap : UncatchableException
 {
   public:
@@ -166,6 +180,8 @@ struct WasmModule
 
 extern "C"
 {
+    void callback_trampoline(void *, void *);
+
     result_t module_load(const uint8_t *mem_ptr, size_t mem_size, callbacks_t callbacks, WasmModule **module_out)
     {
         *module_out = new WasmModule(mem_ptr, mem_size, callbacks);
@@ -192,6 +208,12 @@ extern "C"
         throw UserException(data, vtable);
     }
 
+    // Throw a pointer that's assumed to be codegen::BreakpointHandler on the
+    // rust side.
+    [[noreturn]] void throw_breakpoint(uintptr_t callback) {
+        throw BreakpointException(callback);
+    }
+
     bool invoke_trampoline(
         trampoline_t trampoline,
         void *ctx,
@@ -217,6 +239,10 @@ extern "C"
             *user_error = e.error_data;
             return false;
         }
+        catch (const BreakpointException &e) {
+            callback_trampoline(user_error, (void *)e.callback);
+            return false;
+        }
         catch (const WasmException &e)
         {
             *trap_out = WasmTrap::Type::Unknown;
@@ -233,4 +259,4 @@ extern "C"
     {
         return module->get_func(llvm::StringRef(name));
     }
-}
+}

lib/llvm-backend/src/backend.rs

@@ -39,7 +39,8 @@ extern "C" {
     fn module_delete(module: *mut LLVMModule);
     fn get_func_symbol(module: *mut LLVMModule, name: *const c_char) -> *const vm::Func;
 
-    fn throw_trap(ty: i32);
+    fn throw_trap(ty: i32) -> !;
+    fn throw_breakpoint(ty: i64) -> !;
 
     /// This should be the same as spliting up the fat pointer into two arguments,
     /// but this is cleaner, I think?
@@ -103,6 +104,7 @@ fn get_callbacks() -> Callbacks {
             fn_name!("vm.memory.size.static.local") => vmcalls::local_static_memory_size as _,
 
             fn_name!("vm.exception.trap") => throw_trap as _,
+            fn_name!("vm.breakpoint") => throw_breakpoint as _,
 
             _ => ptr::null(),
         }

lib/llvm-backend/src/code.rs

@@ -496,6 +496,21 @@ pub struct CodegenError {
     pub message: String,
 }
 
+// This is only called by C++ code, the 'pub' + '#[no_mangle]' combination
+// prevents unused function elimination.
+#[no_mangle]
+pub unsafe extern "C" fn callback_trampoline(
+    b: *mut Option<Box<dyn std::any::Any>>,
+    callback: *mut BreakpointHandler,
+) {
+    let callback = Box::from_raw(callback);
+    let result: Result<(), Box<dyn std::any::Any>> = callback(BreakpointInfo { fault: None });
+    match result {
+        Ok(()) => *b = None,
+        Err(e) => *b = Some(e),
+    }
+}
+
 pub struct LLVMModuleCodeGenerator {
     context: Option<Context>,
     builder: Option<Builder>,
@@ -612,7 +627,14 @@ impl FunctionCodeGenerator<CodegenError> for LLVMFunctionCodeGenerator {
                     InternalEvent::FunctionBegin(_) | InternalEvent::FunctionEnd => {
                         return Ok(());
                     }
-                    InternalEvent::Breakpoint(_callback) => {
+                    InternalEvent::Breakpoint(callback) => {
+                        let raw = Box::into_raw(Box::new(callback)) as u64;
+                        let callback = intrinsics.i64_ty.const_int(raw, false);
+                        builder.build_call(
+                            intrinsics.throw_breakpoint,
+                            &[callback.as_basic_value_enum()],
+                            "",
+                        );
                         return Ok(());
                     }
                     InternalEvent::GetInternal(idx) => {

lib/llvm-backend/src/intrinsics.rs

@@ -147,6 +147,7 @@ pub struct Intrinsics {
     pub memory_size_shared_import: FunctionValue,
 
     pub throw_trap: FunctionValue,
+    pub throw_breakpoint: FunctionValue,
 
     pub ctx_ptr_ty: PointerType,
 }
@@ -309,7 +310,6 @@ impl Intrinsics {
             i32_ty.fn_type(&[ctx_ptr_ty.as_basic_type_enum(), i32_ty_basic], false);
 
         let ret_i1_take_i1_i1 = i1_ty.fn_type(&[i1_ty_basic, i1_ty_basic], false);
-
         Self {
             ctlz_i32: module.add_function("llvm.ctlz.i32", ret_i32_take_i32_i1, None),
             ctlz_i64: module.add_function("llvm.ctlz.i64", ret_i64_take_i64_i1, None),
@@ -525,6 +525,11 @@ impl Intrinsics {
                 void_ty.fn_type(&[i32_ty_basic], false),
                 None,
             ),
+            throw_breakpoint: module.add_function(
+                "vm.breakpoint",
+                void_ty.fn_type(&[i64_ty_basic], false),
+                None,
+            ),
             ctx_ptr_ty,
         }
     }

lib/middleware-common/src/metering.rs

@@ -129,7 +129,7 @@ pub fn set_points_used_ctx(ctx: &mut Ctx, value: u64) {
     ctx.set_internal(&INTERNAL_FIELD, value);
 }
 
-#[cfg(all(test, feature = "singlepass"))]
+#[cfg(all(test, any(feature = "singlepass", feature = "llvm")))]
 mod tests {
     use super::*;
     use wabt::wat2wasm;