wasm-micro-runtime/core/iwasm/doc/wasm_exports.MD

Wasm exports

The internal data structure for Wasm exports:

Setup exports for Module

The array data structure pointed by WASMModule::exports is setup during loading a module. Basically the runtime will load the exports sections from the module file content, and construct an array of C struct WASMExport.

A WASMExport item contains three elements that map the Wasm file exports section structure:

• name: the name shown to external
• kind: total 4 export types: function, globals, memory, table
• index: As all the 4 export types are organized in array, this refers to index in target export type

Function exports

use function exports

function exports are often used in two situations:

1. **call by host**: runtime API `wasm_runtime_lookup_function` will walk through the array of `WASMModuleInstance::export_functions` and compare the exported name with given target symbol name in the function parameter. If any array item matches the name, it then returns the value of field `function` which points to associated function instance (WASMFunctionInstance)  
2. **import by another module**: During linking multiple modules, the runtime saves the pointer of exported WASMFunctionInstance in the local WASMFunctionInstance of importing module.

setup for instance

The data structure pointed by WASMModuleInstance::export_functions is set up during instantiating module instance.

The runtime will walk through the WASMModule::exports array and find all the item with kind equal to "function". Create a node of WASMExportFuncInstance for each matching, find the associated WASMFunctionInstance object and save its address in the field function.