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.

Dynamic program analyses help in understanding a program’s runtime behavior and detect issues related to security, program comprehension, or profiling. Instrumentation platforms aid analysis developers by offering a high-level API to write the analysis, and inserting the analysis into the target program. However, current instrumentation platforms for WebAssembly (Wasm) restrict analysis portability because they require concrete runtime environments. Moreover, their analysis API only allows the development of analyses that observe the target program but cannot modify it. As a result, many popular dynamic analyses present for other languages, such as runtime hardening, virtual patching or runtime optimization, cannot currently be implemented for Wasm atop a dynamic analysis platform. Instead, they need to be built manually, which requires knowledge of low-level details of the Wasm’s semantics and instruction set, and how to safely manipulate it. This paper introduces Wastrumentation, the first dynamic analysis platform for WebAssembly that supports intercession. Our solution, based on source code instrumentation, weaves the analysis code directly into the target program code. Inlining the analysis into the target’s source code avoids dependencies on the runtime environment, making analyses portable across Wasm VMs. Moreover, it enables the implementation of analyses in any Wasm-compatible language. We evaluate our solution in two ways. First, we compare it against a state-of-the-art source code instrumentation platform using the WasmR3 benchmarks. The results show improved memory consumption and competitive performance overhead. Second, we develop an extensive portfolio of dynamic analyses, including novel analyses previously unattainable with source code instrumentation platforms, such as memoization, safe heap access, and the removal of NaN non-determinism.