The internal data structure for Wasm exports:
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 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.
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.