When instantiating a WebAssembly module, it might operate on a newly created linear memory or it might continue operation on a linear memory provided by the environment. An app would instantiate global, static constructors (C++) at start-time, whereas calling a function of an library would not (lemma: avoid global static constructors if you want to translate C++ to WebAssembly). The linear memory is the sandbox the WebAssembly module may operate on, storing the static data in an indexed region, managing the stack memory and managing the dynamic memory required by the app during runtime.Ī WebAssembly module could be a library only or an app the latter requiring a start-function in the module. The linear memory of WebAssembly can be compared to the virtual memory provided to processes running on Windows or Linux. This is achieved by sandboxing the code, operating on a so called linear memory only. The security model of WebAssembly has the important goal to protect users from buggy or malicious modules. If developing portable WebAssembly modules/apps it is crucial to understand the management of static and dynamic memory and the influence of the compiler toolchain being used. (Note: avoid emscripten if your code has to deal with int64-primitives, as Javascript would emulate those using floats). Emscripten will translate the C/C++ to JavaScript first and this translating to WebAssembly, whereas clang would translate from C/C++ directly to WebAssembly. High level source code (C/C++/Rust) is compiled to WebAssembly using toolchains like emscripten, clang, or rustc. The code being used for the investigation is accessible at My intention is find the best toolchain to produce WebAssembly-modules being as portable as possible.

This document will focus onto the latter one, the dynamic memory and how it is realized by different toolchains compiling C/C++/Rust targeting the WebAssembly architecture/platform. Stack memory allocation refers to a memory region where data is added or removed per function-scope in a last-in-first-out (LIFO) manner.ĭynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely malloc, realloc, calloc and free or the corresponding boxing in Rust. Static memory allocation refers to assignment of fixed memory addresses during compile and start-time of an application (.data or. These high-level languages like C/C++/Rust (+Javascript) deal with different allocations of memory, such as static memory, stack memory and dynamic memory. Wasm is designed as a portable target for compilation of high-level languages like C/C++/Rust, enabling deployment on the web for client and server applications. WebAssembly is a binary instruction format for a stack-based virtual machine.

Fn 1905 assembly instructions