github.com/bananabytelabs/wazero@v0.0.0-20240105073314-54b22a776da8/site/content/docs/_index.md (about) 1 +++ 2 title = "Docs" 3 layout = "single" 4 +++ 5 6 ## Overview 7 8 WebAssembly is a way to safely run code compiled in other languages. 9 Runtimes execute WebAssembly Modules (Wasm), which are most often binaries with a `.wasm` extension. 10 Most WebAssembly modules import functions from the host, to perform tasks that are otherwise disallowed by their sandbox. 11 The most commonly imported functions are called WASI, which allow access to system resources such as the console or files. 12 13 wazero is a WebAssembly runtime, written completely in Go. It has no platform dependencies, so can be used in any environment supported by Go. 14 15 ## API 16 17 Being a Go library, which we document wazero's API via [godoc][godoc]. 18 19 ## Terminology 20 21 Wazero has consistent terminology used inside the codebase which may be new to you, or different than another WebAssembly runtime. 22 This section covers the most commonly used vocabulary. Terms rarely used may also be defined inline in individual sections. 23 24 * Host - Host is a WebAssembly concept that refers to the process that embeds a WebAssembly runtime. In wazero, the host is a program written in Go. 25 * Binary - Binary is a WebAssembly module, compiled from source such as C, Rust or Tinygo. This is also called Wasm or a guest, and usually is a file with a `.wasm` extension. This is the code wazero runs. 26 * Sandbox - Sandbox is a term that describes isolation. For example, a WebAssembly module, defined below, is isolated from the host memory and memory of other modules. This means it cannot corrupt the calling process or cause it to crash. 27 * [Module][Module] - Module an instance of a Binary, which usually exports functions that can be invoked by the embedder. It can also import functions from the host to perform tasks not defined in the WebAssembly Core Specification, such as I/O. 28 * Host Module - Host Module is a wazero concept that represents a collection of exported functions that give functionality not provided in the WebAssembly Core Specification, such as I/O. These exported functions are defined as normal Go functions (including closures). For example, WASI is often used to describe a host module named "wasi_snapshot_preview1". 29 * Exported Function - An Exported Function is a function addressable by name. Guests can import functions from a host module, and export them so that Go applications can call them. 30 * [Runtime][Runtime] - Runtime is the top-level component in wazero that compiles binaries, configures host functions, and runs guests in sandboxes. How it behaves is determined by its engine: interpreter or compiler. 31 * Compile - In wazero, compile means prepares a binary, or a host module to be instantiated. This is implemented differently based on whether a runtime is a compiler or an interpreter. 32 * [Compiled Module][CompiledModule] - a prepared and ready to be instantiated object created vi Compilation phrase. This can be used in instantiation multiple times to create multiple and isolated sandbox from a single Wasm binary. 33 * Instantiate - In wazero, instantiate means allocating a [Compiled Module][CompiledModule] and associating it with a unique name, resulting in a [Module][Module]. This includes running any start functions. The result of instantiation is a module whose exported functions can be called. 34 35 ## Architecture 36 37 This section covers the library architecture wazero uses to implements the WebAssembly Core specification and WASI. 38 Features unique to Go or wazero are discussed where architecture affecting. 39 40 ### Components 41 42 At a high level, wazero exposes a [Runtime][Runtime], which can compile the binary into [Compiled Module][CompiledModule], 43 and instantiate it as a sandboxed [Module][Module]. 44 These sandboxed modules are isolated from each other (modulo imports) and the embedding Go program. In a sandbox, 45 there are 4 types of objects: memory, global, table, and function. Functions might be exported by name, and they can be executed by 46 the embedding Go programs. During the execution of a function, the objects in the sandbox will be accessed, for example, 47 a Wasm function can read and write from the memory object in the sandbox. The same goes for globals and tables. 48 49 Here's a diagram showing the relationship between these components. 50 51 ```goat 52 | Access during execution 53 | +--------+-------+-----------+ 54 | | | | +---| 55 | | | | | | 56 | v v v v | 57 | (Memory, Globals, Table, Functions) 58 Wasm Binary | | ^ 59 | | | | 60 +----------+ v +--------------------+ | 1 : N +------------------+ | 61 | Runtime | ----> | Compiled Module |----|-----------> | Module | | 62 +----------+ +--------------------+ | Instantiate +------------------+ | 63 | | | 64 | | 1 : N | 65 | v | 66 | +-------------------+ | 67 | | Exported Function |---+ 68 | +-------------------+ 69 | 70 | 71 compile time | runtime 72 | 73 ``` 74 75 76 ### Host access 77 78 First, a Wasm module can require the import of functions at instantiation phrase. 79 Such import requirements are included in the original Wasm binary. For example, 80 81 ```wat 82 (module (import "env" "foo" (func))) 83 ``` 84 85 this WebAssembly module requires importing the exported function named `foo` from the instantiated module named `env`. 86 An imported functions can be called by the importing modules, and this is how a Wasm module interacts with the outside of 87 its own sandbox. 88 89 In wazero, the imported modules can be Host Modules which consist of Go functions. Therefore, 90 the importing modules can invoke Go functions defined by the embedding Go programs. 91 The notable example of this imported host module is wazero's [`wasi_snapshot_preview1`][wasi] module which provides 92 the system calls to wasm modules because the Wasm specification itself doesn't define system calls. This way, Wasm modules 93 are granted the ability to do, for example, file system access, etc. 94 95 Here's the diagram of how a Wasm module accesses Go functions: 96 97 ```goat 98 func add(foo, bar int32) int32 { 99 return foo + bar 100 } | 101 | 102 | implements 103 host module v 104 +---------+ +------------------+ +-----------------+ 105 | Runtime | -------------> | (module: myhost) | -------> | (function: add) | 106 +---------+ ^ +------------------+ export +-----------------+ 107 \ / / 108 \instantiate / 109 \ / / 110 \ v / 111 \ / 112 \ / imported 113 \ (import "myhost" "add" (func)) / 114 \ / 115 \ +-----------/------+ 116 \ | v | 117 \ | (myhost.add) | 118 v | ^ | 119 +--------------------+ | | call | 120 | (module: need_add) |--------->| (export:use_add) <----- Exported 121 +--------------------+ | | 122 +------------------+ 123 functions in need_add's sandbox 124 ``` 125 126 In this example diagram, we instantiated a host module named `myhost` which consists of a Go function `add`, and it exports 127 the Go function under the name `add`. Then, we instantiate the Wasm module which requires importing function whose module is `mymodule` 128 and name is `add`. This case, the import target module instance and function already exists, and therefore the resulting sandbox contains 129 the imported function in its sandbox. Finally, the importing module exports the function named `use_add` which in turns calls the imported function, 130 therefore, we can freely access the imported Go function from the importing Wasm module. 131 132 Here's [the working example in wazero repository][age-calculator], so please check it out for more details. 133 134 135 ### Engine 136 137 There's a concept called "engine" in wazero's codebase. It is in charge of how wazero compiles the raw Wasm binary, transforms it into 138 intermediate data structure, caches the compiled information, and performs function calls of Wasm functions. 139 Notably, the interpreter and compiler in wazero's [Runtime configuration][RuntimeConfig] refer to the type of engine tied to [Runtime][Runtime]. 140 141 #### Compiler 142 143 In wazero, a compiler is a runtime configured to compile modules to platform-specific machine code ahead of time (AOT) 144 during the creation of [CompiledModule][CompiledModule]. This means your WebAssembly functions execute 145 natively at runtime of the embedding Go program. Compiler is faster than Interpreter, often by order of 146 magnitude (10x) or more, and therefore enabled by default whenever available. 147 148 #### Interpreter 149 150 Interpreter is a naive interpreter-based implementation of Wasm virtual machine. 151 Its implementation doesn't have any platform (GOARCH, GOOS) specific code, 152 therefore interpreter can be used for any compilation target available for Go (such as riscv64). 153 154 ## How do function calls work? 155 156 WebAssembly runtimes let you call functions defined in wasm. How this works in 157 wazero is different depending on your `RuntimeConfig`. 158 159 * `RuntimeConfigCompiler` compiles machine code from your wasm, and jumps to 160 that when invoking a function. 161 * `RuntimeConfigInterpreter` does not generate code. It interprets wasm and 162 executes go statements that correspond to WebAssembly instructions. 163 164 How the compiler works precisely is a large topic. If you are interested in 165 digging deeper, please look at [the dedicated documentation]({{< relref "/how_do_compiler_functions_work.md" >}}) 166 on this topic! 167 168 ## Rationales behind wazero 169 170 Please refer to [RATIONALE][rationale] for the notable rationales behind wazero's implementations. 171 172 [Module]: https://pkg.go.dev/github.com/bananabytelabs/wazero@v1.0.0-rc.1/api#Module 173 [Runtime]: https://pkg.go.dev/github.com/bananabytelabs/wazero#Runtime 174 [RuntimeConfig]: https://pkg.go.dev/github.com/bananabytelabs/wazero#RuntimeConfig 175 [CompiledModule]: https://pkg.go.dev/github.com/bananabytelabs/wazero#CompiledModule 176 [godoc]: https://pkg.go.dev/github.com/bananabytelabs/wazero 177 [rationale]: https://github.com/bananabytelabs/wazero/blob/main/RATIONALE.md 178 [wasi]: https://github.com/bananabytelabs/wazero/tree/main/imports/wasi_snapshot_preview1/example 179 [age-calculator]: https://github.com/bananabytelabs/wazero/blob/v1.0.0-rc.1/examples/import-go/age-calculator.go