I’ll be presenting WebAssembly Debugging with LLDB in the LLVM Dev Room at FOSDEM 26 on Saturday, January 31st. Abstract WebAssembly support in Swift started as a community project and became an official part of Swift 6.2. As Swift on WebAssembly matures, developers need robust debugging tools to match. This talk presents our work adding native debugging support for Swift targeting Wasm in LLDB. WebAssembly has some unique characteristics, such as its segmented memory address space, and we’ll explore how we made that work with LLDB’s architecture....

This post describes how to debug WebAssembly code running under the WebAssembly Micro Runtime (WAMR) on macOS. WAMR is a lightweight WebAssembly runtime designed for embedded and IoT applications, but its simplicity and debugging support make it well suited for general development. Building the WebAssembly Micro Runtime We have to build the runtime with debugging support. Start by cloning the wasm-micro-runtime repository and optionally checkout a specific release. $ git clone git@github....

WebAssembly (Wasm) is a low-level binary instruction format. It was originally created to run in the browser, but has gained traction in many non-browser environments as well. Debugging WebAssembly applications presents unique challenges compared to traditional native code debugging. Unlike native executables that run directly on the processor, WebAssembly code executes within a virtual machine that abstracts away the underlying hardware. This abstraction, while providing portability and security benefits, complicates the debugging process because debuggers cannot rely on standard debugging techniques....

I was recently answering questions about dsymutil’s multi-threading model and lockstep algorithm. I decided to write it down here for future reference. This article focuses on types and the .debug_info section. Background As a reminder, dsymutil is an optimizing DWARF linker. It only retains debug info for elements that appear in the final executable. It uses the One Definition Rule (ODR) to unique C++ types. As will become clear, both of these heavily shaped its design....

Mach-O (Mach Object) is a binary file format used by macOS and iOS for executables, libraries, and object code. A Mach-O file consists of a header, followed by a series of load commands, and then a series of segments. The 4GB Limitations The original 32-bit format used 32-bit offsets, which can address a maximum of 2^32 bytes, or 4GB of memory. The 64-bit variant uses 64-bit offsets, vastly increasing the addressable memory space....

Debug Adapter Protocol The Debug Adapter Protocol (DAP) defines a generic protocol for editors to talk to a debugger. Popular editors with DAP support include Visual Studio Code, Sublime Text, (Neo)vim and Emacs. If you’re familiar with the Language Server Protocol (LSP) you can think of DAP like LSP, but for debugging. Implementations of the debug adapter protocol generally come in two forms: An extension tailored to a specific editor. A standalone DAP server that can be used with any editor that supports the protocol....

LLVM is once again participating in Google Summer of Code (GSOC). For 2024 we have an exciting project to enrich the disassembler in LLDB. The project consists of using the variable location information from the debug info (DWARF) to annotate LLDB’s disassembler (and register read) output with the location and lifetime of source variables. You can find all the details on LLVM’s Google Summer of Code Ideas & Projects page....

Today Google announced the list of open-source organizations participating in the 2021 Google Summer of Code program. Together with Raphael and Pedro, I’ll be mentoring the following two projects: A structured approach to diagnostics in LLDB Lua scripted watchpoints in LLDB If you’re interested in either of these projects or have questions, feel free to reach out. For more information about GSoC itself check out the Summer of Code website.

To make incremental builds fast on macOS, the static linker (ld) ignores the debug information. It can easily be a magnitude bigger than the rest of the program and slow down link time. Instead the linker emits a debug map which contains the location of all the object files it relocated so that debug info consumers (such as the debugger) know where to find the DWARF debug info. This approach works great during development and greatly speeds up the build-debug cycle....