WebAssembly has established itself as a portable compilation target across a wide variety of environments, from browsers and cloud platforms to hardware-constrained devices such as microcontrollers.Its formal specification enables developers to reliably target a broad range of runtimes while compiler toolchains and runtime developers rely on the same formal model.Yet debugging support for WebAssembly remains at an early stage.Source maps often lack sufficient context for debugging, whereas DWARF offers rich type, scope, and location data that developers need for effective debugging.However, adding DWARF support requires non-trivial, timeconsuming runtime-specific efforts that must be repeated independently for each runtime.As a result, the set of debugging features available across runtimes is highly fragmented, while bugs that manifest exclusively in environments without debugging support cannot be analyzed at all.In this paper, we present DWasm, a runtime-independent debugger for WebAssembly.DWasm is realized as a binary transformation pass that instruments the target application with debugging support, without being implemented as part of a concrete runtime engine.By decoupling the debugger from the runtime, DWasm brings portable, DWARFbased debugging across WebAssembly environments.This approach further reduces tool development costs and enables debugging features to be customized for the applicationruntime combination at hand.For our benchmark programs, DWasm exhibits 2x memory overhead, which is low when compared with state-of-the-art debuggers for WebAssembly.In contrast, we observe a performance overhead consistently over 300x, where the shadow-execution instrumentation dominates the added overhead.

Debugging embedded systems is difficult due to the restricted resources available, and the hard to reproduce bugs. Moreover, few debugging facilities are available for constrained devices. To address this, we build upon a recent technique for big data applications, called out-of-place debugging.

Debugging IoT applications is challenging due to the hardware constraints of IoT devices, making advanced techniques like record-replay debugging impractical. As a result, programmers often rely on manual resets or inefficient and time-consuming debugging techniques such as printf. Although simulators can help in that regard, their applicability is limited because they fall short of accurately simulating and reproducing the runtime conditions where bugs appear. In this work, we explore a novel debugging approach called event-based out-of-place debugging in which developers can capture a remotely running program and debug it locally on a (more powerful) machine. Our approach thus provides rich debugging features (e.g., step-back) that normally would not run on the hardware restricted devices. Two different strategies are offered to deal with resources which cannot be easily transferred (e.g., sensors): pull-based (akin to remote debugging), or push-based (where data updates are pushed to developer’s machine during the debug session). We present EDWARD, an event-based out-of-place debugger prototype, implemented by extending the WARDuino WebAssembly microcontroller Virtual Machine, that has been integrated into Visual Studio Code. To validate our approach, we show how our debugger helps uncover IoT bugs representative of real-world applications through several use-case applications. Initial benchmarks show that event-based out-of-place debugging can drastically reduce debugging latency.