Wasmer Features

The Wasmer WebAssembly runtime provides various features for users and developers:

• Compilers: Wasmer supports multiple compilers: Singlepass, Cranelift and LLVM. Each of these have different tradeoffs of compilation speed vs runtime speed;

• Caching: compiled WebAssembly modules can be reused so subsequent runs of a Wasm file will have very little start up time;

• Metering: computation time and other resources can be monitored and limits set to control how the Wasm code runs. This is also known as "gas metering";

• WebAssembly Features:

  • Bulk-memory operations: e.g. instructions with behavior similar to C's memmove and memset in WebAssembly;

  • Multi-value return: return multiple values from functions making data transfer between host and guest simpler;

  • Import & export of mutable globals: adds ability to import and export mutable globals;

  • Non-trapping float-to-int conversions: this proposal would establish a convention for saturating operations, to avoid introducing trapping;

  • Sign-extension operations: adds five new integer instructions for sign-extending 8-bit, 16-bit, and 32-bit values;

  • Reference types: easier and more efficient interop with host environment;

  • SIMD: Single Instruction, Multiple data: do heavy number crunching more quickly and/or with lower power usage.

  • Threads: adds a new shared linear memory type and some new operations for atomic memory access;

• ABIs: it allows running different types of programs compiled to WebAssembly, with ABIs such as:

  • Emscripten

  • WASI

Support of features by Compiler

Runtime features:

	Singlepass	Cranelift	LLVM
Emscripten	✅	✅	✅
WASI	✅	✅	✅

WebAssembly features:

	Singlepass	Cranelift	LLVM
Bulk memory operations	✅	✅	✅
Multi-value return	🔄	✅	✅
Import & export of mutable globals	✅	✅	✅
Non-trapping float-to-int conversions	✅	✅	✅
Sign-extension operations	✅	✅	✅
Reference types (Phase 4)	🔄	🔄	🔄
SIMD (Phase 3)	⬜	✅	✅
Threads (Phase 2)	✅	🔄	✅

Legend

• ✅ Supported

• 🔄 In the works

• ⬜ Not yet supported (please ping us if you need this feature!)

Support by Operating System

	Linux	macOS	Windows
Cranelift	✅	✅	✅
LLVM	✅	✅	✅
Singlepass	✅	✅	#347
WASI	✅	✅	✅*

• poll_fd is not fully implemented for Windows yet

Compiler Support by Chipset

	x86_64	arm64	x86
Cranelift	✅	✅	✅
LLVM	✅	✅	✅
Singlepass	✅	🔄	⬜

Language Embeddings

Wasmer enables WebAssembly usage in a lot of different languages. Here are some of the features in each of those:

	Rust	C / C++	Go	Python	Ruby
Terminate in host call	✅	⬜	⬜	⬜	⬜
WASI	✅	✅	✅	✅	⬜
WASI FS API	✅	⬜	⬜	⬜	⬜
Serialize/Deserialize	✅	✅	✅	✅	⬜
Metering	✅	⬜	⬜	⬜	⬜