Chris Wellons

  1. Parameterized types in C using the new tag compatibility rule

    C23 has a new rule for struct, union, and enum compatibility finally appearing in compilers starting with GCC 15, released this past April, and Clang later this year. The same struct defined in different translation units (TU) has always been compatible — essential to how they work. Until this rule change…

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  2. WebAssembly: How to allocate your allocator

    An early, small hurdle diving into WebAssembly was allocating my allocator. On a server or desktop with virtual memory, the allocator asks the operating system to map fresh pages into its address space (sbrk, anonymous mmap, VirtualAlloc), which it then dynamically allocates to different purposes. In…

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  3. Lessons learned from my first dive into WebAssembly

    It began as a water sort puzzle solver, constructed similarly to my British Square solver. It was nearly playable, so I added a user interface with SDL2. My wife enjoyed it on her desktop, but wished to play on her phone. So then I needed to either rewrite it in JavaScript and hope the solver was still…

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  4. A more robust raw OpenBSD syscall demo

    Ted Unangst published dude, where are your syscalls? on flak yesterday, with a neat demonstration of OpenBSD’s pinsyscall security feature, whereby only pre-registered addresses are allowed to make system calls. Whether it strengthens or weakens security is up for debate, but regardless it’s an interesting…

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  5. Robust Wavefront OBJ model parsing in C

    Wavefront OBJ is a line-oriented, text format for 3D geometry. It’s widely supported by modeling software, easy to parse, and trivial to emit, much like Netpbm for 2D image data. Poke around hobby 3D graphics projects and you’re likely to find a bespoke OBJ parser. While typically only loading their…

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  6. Meet the new xxd for w64devkit: rexxd

    xxd is a versatile hexdump utility with a “reverse” feature, originally written between 1990–1996. The Vim project soon adopted it, and it’s lived there ever since. If you have Vim, you also have xxd. Its primary use cases are (1) the basis for a hex editor due to its -r reverse option that can unhexdump…

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  7. Tips for more effective fuzz testing with AFL++

    Fuzz testing is incredibly effective for mechanically discovering software defects, yet remains underused and neglected. Pick any program that must gracefully accept complex input, written in any language, which has not yet been been fuzzed, and fuzz testing usually reveals at least one bug. At least…

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  8. Examples of quick hash tables and dynamic arrays in C

    This article durably captures my reddit comment showing techniques for std::unordered_map and std::vector equivalents in C programs. The core, important features of these data structures require only a dozen or so lines of code apiece. They compile quickly, and tend to run faster in debug builds than…

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