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Webassembly Static Instrumenter

A convenient library to read and freely instrument WASM code statically. The repository is mostly up-to-date with the latest WASM standards -- including support for threading/atomics and bulk memory instructions

Building

cmake -B build
make -C build

Sample instrumentation

Examples of routines can be found in routines.cpp. Support for more complex views is still in progress, but currently implemented APIs can be found in views.cpp

The sample_instrument method below covers basic usage of the APIs. You only need to import ir.h and instructions.h for basic functionality.

#include "ir.h"
#include "instructions.h"

void sample_instrument (WasmModule& module) {
  /* Global inmodule */
  GlobalDecl global = { 
    .type = WASM_TYPE_I32, 
    .is_mutable = true,
    .init_expr_bytes = INIT_EXPR (I32_CONST, 5)
  };
  module.add_global(global, "inmodule_global");

  /* Global import */
  ImportInfo iminfo = {
    .mod_name = "instrumentest",
    .member_name = "newglob"
  };
  GlobalInfo imglob = {
    .type = WASM_TYPE_EXTERNREF,
    .is_mutable = false
  };
  module.add_import(iminfo, imglob);

  /* Function import */
  iminfo.member_name = "newfunc";
  SigDecl imfunc = {
    .params = {WASM_TYPE_I32},
    .results = {WASM_TYPE_F64}
  };
  ImportDecl* func_imp = module.add_import(iminfo, imfunc);

  /* Export find */
  ExportDecl* exp = module.find_export("printf");
  if (exp == NULL) {
    TRACE("Printf not found\n");
  }

  /* Add a I32 Const + Drop before every call in main */
  ExportDecl* main_exp = module.find_export("main");
  FuncDecl* main_fn = main_exp->desc.func;
  InstList &insts = main_fn->instructions;
  for (auto institr = insts.begin(); institr != insts.end(); ++institr) {
    InstBasePtr &instruction = *institr;
    if (instruction->is(WASM_OP_CALL)) {
      insts.insert(institr, InstBasePtr(new I32ConstInst(0xDEADBEEF)));
      insts.insert(institr, InstBasePtr(new DropInst()));
    }
  }
}

API Methods

Webassembly has the following index spaces -- GlobalDecl, TableDecl, MemoryDecl, FuncDecl. The folllowing specifications will use [ISD] to denote these in below APIs. Refer to ir.h for details

Addition Operations

Add to Index Space

[ISD]* add_[ISD] ([ISD] &decl, const char* export_name = NULL);

Add Import

ImportDecl* add_import (ImportInfo &info, [ISD] &decl);

Add Export

ExportDecl* add_export (std::string export_name, [ISD] &var);

Find Operations

Find Export

ExportDecl* find_export (std::string export_name);

Working with instructions

Each function has an InstList object to iterate over instructions. Since it uses a standard list, all instructions iterators are preserved when inserting/removing from the structure. All supported instructions and their constructors can be found here.