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Calling Exported Functions

The --call Flag​

Use -c or --call to invoke a specific exported function by name instead of the default entry point:

wasmrun exec ./module.wasm --call <FUNCTION_NAME> [ARGS...]
wasmrun exec ./module.wasm -c <FUNCTION_NAME> [ARGS...]

How It Works​

  1. The executor parses the module and looks up the export by name
  2. Verifies the export is a function (not a memory, table, or global)
  3. Reads the function's type signature (parameter types and return types)
  4. Pops the provided arguments from the command line, converts them to WASM values
  5. Calls the function and returns the result

Examples​

Call a Simple Function​

# Module exports: add(i32, i32) → i32
wasmrun exec ./math.wasm --call add 10 20

Call Without Arguments​

# Module exports: get_version() → i32
wasmrun exec ./lib.wasm --call get_version

Call a Void Function​

# Module exports: initialize() → void
wasmrun exec ./app.wasm --call initialize

Multiple Functions in One Module​

A single WASM module can export many functions. Use inspect to discover them:

# See all exports
wasmrun inspect ./math.wasm
# 📤 Exports:
#    add       : function [index 0]
#    multiply  : function [index 1]
#    factorial : function [index 2]
#    _start    : function [index 3]

# Call any of them
wasmrun exec ./math.wasm --call add 5 3
wasmrun exec ./math.wasm --call multiply 6 7
wasmrun exec ./math.wasm --call factorial 10

Error Handling​

Function Not Found​

wasmrun exec ./module.wasm --call nonexistent
# ❌ Exported function 'nonexistent' not found in WASM module

Not a Function Export​

If the name maps to a memory or table export rather than a function, you'll get an error. Use wasmrun inspect to verify the export type.

Wrong Number of Arguments​

The executor passes whatever arguments are provided. If the function signature requires more parameters than given, remaining parameters default to zero. Extra arguments are ignored after conversion.

Discovering Exports​

Before calling functions, inspect the module to see what's available:

wasmrun inspect ./module.wasm

Look at the Export Section for function names, and the Type Section for their signatures.

Use Cases​

Testing Individual Functions​

# Test each exported function during development
wasmrun exec ./lib.wasm --call validate_input 42
wasmrun exec ./lib.wasm --call process_data 100
wasmrun exec ./lib.wasm --call cleanup

Library Modules​

Modules that export utility functions rather than a _start entry point:

# No _start — must use --call
wasmrun exec ./crypto.wasm --call hash_sha256 12345

Benchmarking​

# Time a specific function
time wasmrun exec ./compute.wasm --call heavy_computation 1000000

See Also​