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Exec Mode

Wasmrun's exec mode (wasmrun exec) runs WebAssembly files natively using a built-in interpreter — no browser, no server, just direct execution.

What It Does​

Exec mode is a native WASM runtime that:

  1. Parses the WASM binary (module sections, types, functions, memory, data)
  2. Initializes linear memory and globals
  3. Links WASI syscalls as host functions
  4. Executes the entry point (_start, main, or a specified function)
  5. Returns the exit code
wasmrun exec ./my-program.wasm

When to Use​

  • Running CLI tools compiled to WASM
  • Executing WASM modules without a browser
  • Testing WASM binaries with argument passing
  • Calling specific exported functions from a module

Quick Example​

# Run a WASM file
wasmrun exec ./hello.wasm

# Pass arguments
wasmrun exec ./program.wasm arg1 arg2 arg3

# Call a specific exported function
wasmrun exec ./math.wasm --call add 5 3

Runtime Architecture​

┌─ wasmrun exec ─────────────────────────────────────┐
│                                                     │
│  Module Parser  →  reads .wasm binary sections      │
│       ↓                                             │
│  Executor       →  interprets WASM bytecode         │
│       ↓                                             │
│  Linear Memory  →  64KB pages, bounds-checked       │
│       ↓                                             │
│  WASI Linker    →  host functions (fd_write, etc.)  │
│                                                     │
└─────────────────────────────────────────────────────┘

The interpreter supports all standard WASM instructions: i32/i64/f32/f64 arithmetic, comparison, logic, memory operations, control flow (block/loop/if/br), function calls, and indirect calls via tables.