github.com/AR1011/wazero@v1.0.5/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 ### Host access 76 77 First, a Wasm module can require the import of functions at instantiation phrase. 78 Such import requirements are included in the original Wasm binary. For example, 79 80 ```wat 81 (module (import "env" "foo" (func))) 82 ``` 83 84 this WebAssembly module requires importing the exported function named `foo` from the instantiated module named `env`. 85 An imported functions can be called by the importing modules, and this is how a Wasm module interacts with the outside of 86 its own sandbox. 87 88 In wazero, the imported modules can be Host Modules which consist of Go functions. Therefore, 89 the importing modules can invoke Go functions defined by the embedding Go programs. 90 The notable example of this imported host module is wazero's [`wasi_snapshot_preview1`][wasi] module which provides 91 the system calls to wasm modules because the Wasm specification itself doesn't define system calls. This way, Wasm modules 92 are granted the ability to do, for example, file system access, etc. 93 94 Here's the diagram of how a Wasm module accesses Go functions: 95 96 ```goat 97 func add(foo, bar int32) int32 { 98 return foo + bar 99 } | 100 | 101 | implements 102 host module v 103 +---------+ +------------------+ +-----------------+ 104 | Runtime | -------------> | (module: myhost) | -------> | (function: add) | 105 +---------+ ^ +------------------+ export +-----------------+ 106 \ / / 107 \instantiate / 108 \ / / 109 \ v / 110 \ / 111 \ / imported 112 \ (import "myhost" "add" (func)) / 113 \ / 114 \ +-----------/------+ 115 \ | v | 116 \ | (myhost.add) | 117 v | ^ | 118 +--------------------+ | | call | 119 | (module: need_add) |--------->| (export:use_add) <----- Exported 120 +--------------------+ | | 121 +------------------+ 122 functions in need_add's sandbox 123 ``` 124 125 In this example diagram, we instantiated a host module named `myhost` which consists of a Go function `add`, and it exports 126 the Go function under the name `add`. Then, we instantiate the Wasm module which requires importing function whose module is `mymodule` 127 and name is `add`. This case, the import target module instance and function already exists, and therefore the resulting sandbox contains 128 the imported function in its sandbox. Finally, the importing module exports the function named `use_add` which in turns calls the imported function, 129 therefore, we can freely access the imported Go function from the importing Wasm module. 130 131 Here's [the working example in wazero repository][age-calculator], so please check it out for more details. 132 133 ### Engine 134 135 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 136 intermediate data structure, caches the compiled information, and performs function calls of Wasm functions. 137 Notably, the interpreter and compiler in wazero's [Runtime configuration][RuntimeConfig] refer to the type of engine tied to [Runtime][Runtime]. 138 139 #### Compiler 140 141 In wazero, a compiler is a runtime configured to compile modules to platform-specific machine code ahead of time (AOT) 142 during the creation of [CompiledModule][CompiledModule]. This means your WebAssembly functions execute 143 natively at runtime of the embedding Go program. Compiler is faster than Interpreter, often by order of 144 magnitude (10x) or more, and therefore enabled by default whenever available. 145 146 #### Interpreter 147 148 Interpreter is a naive interpreter-based implementation of Wasm virtual machine. 149 Its implementation doesn't have any platform (GOARCH, GOOS) specific code, 150 therefore interpreter can be used for any compilation target available for Go (such as riscv64). 151 152 ## How do function calls work? 153 154 WebAssembly runtimes let you call functions defined in wasm. How this works in 155 wazero is different depending on your `RuntimeConfig`. 156 157 - `RuntimeConfigCompiler` compiles machine code from your wasm, and jumps to 158 that when invoking a function. 159 - `RuntimeConfigInterpreter` does not generate code. It interprets wasm and 160 executes go statements that correspond to WebAssembly instructions. 161 162 How the compiler works precisely is a large topic. If you are interested in 163 digging deeper, please look at [the dedicated documentation]({{< relref "/how_do_compiler_functions_work.md" >}}) 164 on this topic! 165 166 ## Rationales behind wazero 167 168 Please refer to [RATIONALE][rationale] for the notable rationales behind wazero's implementations. 169 170 [Module]: https://pkg.go.dev/github.com/AR1011/wazero@v1.0.0-rc.1/api#Module 171 [Runtime]: https://pkg.go.dev/github.com/AR1011/wazero#Runtime 172 [RuntimeConfig]: https://pkg.go.dev/github.com/AR1011/wazero#RuntimeConfig 173 [CompiledModule]: https://pkg.go.dev/github.com/AR1011/wazero#CompiledModule 174 [godoc]: https://pkg.go.dev/github.com/AR1011/wazero 175 [rationale]: https://github.com/AR1011/wazero/blob/main/RATIONALE.md 176 [wasi]: https://github.com/AR1011/wazero/tree/main/imports/wasi_snapshot_preview1/example 177 [age-calculator]: https://github.com/AR1011/wazero/blob/v1.0.0-rc.1/examples/import-go/age-calculator.go