Managers

Label Manager

Names generated for Wasm instructions are assigned by the label manager. The latter simply creates a unique identifier on each request.

Memory Manager

Memory manager in Wasm++ uses a first fit approach to allocate linear memory space. The memory manager operates at Wasm-generation time. Thus, addresses can directly be injected inside functions as i32 values. Furthermore, the manager can automatically compute the amount of linear memory pages, of size 64KB each, required by a program.

Example

C++

wasmpp::MemoryManager* mm = new wasmpp::FirstFit();
wasmpp::Memory* name = mm->Allocate(50);            // Allocate 50 bytes to store name string
wasmpp::Memory* age = mm->Allocate(1);              // Allocate 1 byte to store age
printf("Begin address: %d\tEnd address: %d\tSize: %d\n", 
        name->Begin(), name->End(), name->Bytes());
printf("Begin address: %d\tEnd address: %d\tSize: %d\n", 
        age->Begin(), age->End(), age->Bytes());
mm->Free(name);
mm->Free(age);
delete mm;

Output

Begin address: 0   End address: 50  Size: 50
Begin address: 50  End address: 51  Size: 1

Module Manager

A module manager is the container of the memory and label managers, and hosts all the Wasm functions and other sections living on the global scope of a module. This manager also uses functionalities provided by the WABT library such as compiling the IR to WebAssembly bytecode or to Wat format, and validating the correctness of the generated WebAssembly.

Example

C++

using namespace std;
using namespace wabt;
using namespace wasmpp;

int main() {

  // Create a Wasm module
  ModuleManager module;

  // Create a function that loads the value of
  // an i32 address, that is passed as an argument,
  // from the linear memory
  TypeVector params = {Type::I32};
  TypeVector returns = {Type::I32};
  TypeVector locals = {};
  module.MakeFunction("load_example", {params, returns}, locals,
                      [&](FuncBody f, vector<Var> params, std::vector<Var> locals) {
    auto memory_load = MakeI32Load(MakeLocalGet(params[0]));
    f.Insert(memory_load);
  });

  // Create memory section
  uint32_t memory_pages = module.Memory().Pages();
  module.MakeMemory(memory_pages);

  // Validate and generate Wat
  assert(module.Validate());
  bool folded = false;
  bool inline_import_export = true;
  printf("%s\n", module.ToWat(folded, inline_import_export).c_str());
  return 0;
}

Output

(module
  (type (;0;) (func (param i32) (result i32)))
  (func $0 (export "load_example") (param $1 i32) (result i32)
    local.get 0
    i32.load)
  (memory $2 0))