[wasm] Syntax- and Type-aware Fuzzer

This is the beginning of a new fuzzer that generates
correct-by-construction Wasm modules. This should allow us to better
exercise the compiler and correctness aspects of fuzzing. It is based off
of ahaas' original Wasm fuzzer.

At the moment, it can generate expressions made up of most binops, and
also nested blocks with unconditional breaks. Future CLs will add
additional constructs, such as br_if, loops, memory access, etc.

The way the fuzzer works is that it starts with an array of arbitrary
data provided by libfuzzer. It uses the data to generate an expression.
Care is taken to make use of the entire string. Basically, the
generator has a bunch of grammar-like rules for how to construct an
expression of a given type. For example, an i32 can be made by adding
two other i32s, or by wrapping an i64. The process then continues
recursively until all the data is consumed.

We generate an expression from a slice of data as follows:
* If the slice is less than or equal to the size of the type (e.g. 4
  bytes for i32), then it will emit the entire slice as a constant.
* Otherwise, it will consume the first 4 bytes of the slice and use
  this to select which rule to apply. Each rule then consumes the
  remainder of the slice in an appropriate way. For example:
  * Unary ops use the remainder of the slice to generate the argument.
  * Binary ops consume another four bytes and mod this with the length
    of the remaining slice to split the slice into two parts. Each of
    these subslices are then used to generate one of the arguments to
    the binop.
  * Blocks are basically like a unary op, but a stack of block types is
    maintained to facilitate branches. For blocks that end in a break,
    the first four bytes of a slice are used to select the break depth
    and the stack determines what type of expression to generate.
The goal is that once this generator is complete, it will provide a one
to one mapping between binary strings and valid Wasm modules.

Review-Url: https://codereview.chromium.org/2658723006
Cr-Commit-Position: refs/heads/master@{#43289}

BUILD.gn

@@ -3101,3 +3101,23 @@ v8_source_set("wasm_data_section_fuzzer") {
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }
+
+v8_source_set("wasm_compile_fuzzer") {
+  sources = [
+    "test/fuzzer/wasm-compile.cc",
+  ]
+
+  deps = [
+    ":fuzzer_support",
+    ":wasm_module_runner",
+    ":wasm_test_signatures",
+  ]
+
+  configs = [
+    ":external_config",
+    ":internal_config_base",
+  ]
+}
+
+v8_fuzzer("wasm_compile_fuzzer") {
+}

test/fuzzer/fuzzer.gyp

@@ -200,6 +200,35 @@
         '../common/wasm/wasm-module-runner.h',
       ],
     },
+    {
+      'target_name': 'v8_simple_wasm_compile_fuzzer',
+      'type': 'executable',
+      'dependencies': [
+        'wasm_compile_fuzzer_lib',
+      ],
+      'include_dirs': [
+        '../..',
+      ],
+      'sources': [
+        'fuzzer.cc',
+      ],
+    },
+    {
+      'target_name': 'wasm_compile_fuzzer_lib',
+      'type': 'static_library',
+      'dependencies': [
+        'fuzzer_support',
+      ],
+      'include_dirs': [
+        '../..',
+      ],
+      'sources': [  ### gcmole(all) ###
+        'wasm-compile.cc',
+        '../common/wasm/test-signatures.h',
+        '../common/wasm/wasm-module-runner.cc',
+        '../common/wasm/wasm-module-runner.h',
+      ],
+    },
     {
       'target_name': 'v8_simple_wasm_data_section_fuzzer',
       'type': 'executable',

test/fuzzer/fuzzer.isolate

@@ -12,6 +12,7 @@
       '<(PRODUCT_DIR)/v8_simple_wasm_asmjs_fuzzer<(EXECUTABLE_SUFFIX)',
       '<(PRODUCT_DIR)/v8_simple_wasm_call_fuzzer<(EXECUTABLE_SUFFIX)',
       '<(PRODUCT_DIR)/v8_simple_wasm_code_fuzzer<(EXECUTABLE_SUFFIX)',
+      '<(PRODUCT_DIR)/v8_simple_wasm_compile_fuzzer<(EXECUTABLE_SUFFIX)',
       '<(PRODUCT_DIR)/v8_simple_wasm_data_section_fuzzer<(EXECUTABLE_SUFFIX)',
       '<(PRODUCT_DIR)/v8_simple_wasm_function_sigs_section_fuzzer<(EXECUTABLE_SUFFIX)',
       '<(PRODUCT_DIR)/v8_simple_wasm_globals_section_fuzzer<(EXECUTABLE_SUFFIX)',
@@ -28,6 +29,7 @@
       './wasm_asmjs/',
       './wasm_call/',
       './wasm_code/',
+      './wasm_compile/',
       './wasm_data_section/',
       './wasm_function_sigs_section/',
       './wasm_globals_section/',

test/fuzzer/testcfg.py

@@ -19,9 +19,10 @@ class FuzzerVariantGenerator(testsuite.VariantGenerator):
 
 class FuzzerTestSuite(testsuite.TestSuite):
   SUB_TESTS = ( 'json', 'parser', 'regexp', 'wasm', 'wasm_asmjs', 'wasm_call',
-          'wasm_code', 'wasm_data_section', 'wasm_function_sigs_section',
-          'wasm_globals_section', 'wasm_imports_section', 'wasm_memory_section',
-          'wasm_names_section', 'wasm_types_section' )
+          'wasm_code', 'wasm_compile', 'wasm_data_section',
+          'wasm_function_sigs_section', 'wasm_globals_section',
+          'wasm_imports_section', 'wasm_memory_section', 'wasm_names_section',
+          'wasm_types_section' )
 
   def __init__(self, name, root):
     super(FuzzerTestSuite, self).__init__(name, root)

test/fuzzer/wasm-compile.cc

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <algorithm>
+
+#include "include/v8.h"
+#include "src/isolate.h"
+#include "src/objects-inl.h"
+#include "src/objects.h"
+#include "src/ostreams.h"
+#include "src/wasm/wasm-interpreter.h"
+#include "src/wasm/wasm-module-builder.h"
+#include "src/wasm/wasm-module.h"
+#include "test/common/wasm/test-signatures.h"
+#include "test/common/wasm/wasm-module-runner.h"
+#include "test/fuzzer/fuzzer-support.h"
+
+#define WASM_CODE_FUZZER_HASH_SEED 83
+
+typedef uint8_t byte;
+
+using namespace v8::internal::wasm;
+
+namespace {
+
+class DataRange {
+  const uint8_t* data_;
+  size_t size_;
+
+ public:
+  DataRange(const uint8_t* data, size_t size) : data_(data), size_(size) {}
+
+  size_t size() const { return size_; }
+
+  std::pair<DataRange, DataRange> split(uint32_t index) const {
+    return std::make_pair(DataRange(data_, index),
+                          DataRange(data_ + index, size() - index));
+  }
+
+  std::pair<DataRange, DataRange> split() {
+    uint16_t index = get<uint16_t>();
+    if (size() > 0) {
+      index = index % size();
+    } else {
+      index = 0;
+    }
+    return split(index);
+  }
+
+  template <typename T>
+  T get() {
+    if (size() == 0) {
+      return T();
+    } else {
+      const size_t num_bytes = std::min(sizeof(T), size());
+      T result;
+      memcpy(&result, data_, sizeof(num_bytes));
+      data_ += num_bytes;
+      size_ -= num_bytes;
+      return result;
+    }
+  }
+};
+
+class WasmGenerator {
+  template <WasmOpcode Op, ValueType... Args>
+  std::function<void(DataRange)> op() {
+    return [this](DataRange data) {
+      Generate<Args...>(data);
+      builder_->Emit(Op);
+    };
+  }
+
+  template <ValueType T>
+  std::function<void(DataRange)> block() {
+    return [this](DataRange data) {
+      blocks_.push_back(T);
+      builder_->EmitWithU8(
+          kExprBlock, static_cast<uint8_t>(WasmOpcodes::ValueTypeCodeFor(T)));
+      Generate<T>(data);
+      builder_->Emit(kExprEnd);
+      blocks_.pop_back();
+    };
+  }
+
+  template <ValueType T>
+  std::function<void(DataRange)> block_br() {
+    return [this](DataRange data) {
+      blocks_.push_back(T);
+      builder_->EmitWithU8(
+          kExprBlock, static_cast<uint8_t>(WasmOpcodes::ValueTypeCodeFor(T)));
+
+      const uint32_t target_block = data.get<uint32_t>() % blocks_.size();
+      const ValueType break_type = blocks_[target_block];
+
+      Generate(break_type, data);
+      builder_->EmitWithVarInt(kExprBr, target_block);
+      builder_->Emit(kExprEnd);
+      blocks_.pop_back();
+    };
+  }
+
+ public:
+  WasmGenerator(v8::internal::wasm::WasmFunctionBuilder* fn) : builder_(fn) {}
+
+  void Generate(ValueType type, DataRange data);
+
+  template <ValueType T>
+  void Generate(DataRange data);
+
+  template <ValueType T1, ValueType T2, ValueType... Ts>
+  void Generate(DataRange data) {
+    const auto parts = data.split();
+    Generate<T1>(parts.first);
+    Generate<T2, Ts...>(parts.second);
+  }
+
+ private:
+  v8::internal::wasm::WasmFunctionBuilder* builder_;
+  std::vector<ValueType> blocks_;
+};
+
+template <>
+void WasmGenerator::Generate<kWasmI32>(DataRange data) {
+  if (data.size() <= sizeof(uint32_t)) {
+    builder_->EmitI32Const(data.get<uint32_t>());
+  } else {
+    const std::function<void(DataRange)> alternates[] = {
+        op<kExprI32Eqz, kWasmI32>(),  //
+        op<kExprI32Eq, kWasmI32, kWasmI32>(),
+        op<kExprI32Ne, kWasmI32, kWasmI32>(),
+        op<kExprI32LtS, kWasmI32, kWasmI32>(),
+        op<kExprI32LtU, kWasmI32, kWasmI32>(),
+        op<kExprI32GeS, kWasmI32, kWasmI32>(),
+        op<kExprI32GeU, kWasmI32, kWasmI32>(),
+
+        op<kExprI64Eqz, kWasmI64>(),  //
+        op<kExprI64Eq, kWasmI64, kWasmI64>(),
+        op<kExprI64Ne, kWasmI64, kWasmI64>(),
+        op<kExprI64LtS, kWasmI64, kWasmI64>(),
+        op<kExprI64LtU, kWasmI64, kWasmI64>(),
+        op<kExprI64GeS, kWasmI64, kWasmI64>(),
+        op<kExprI64GeU, kWasmI64, kWasmI64>(),
+
+        op<kExprF32Eq, kWasmF32, kWasmF32>(),
+        op<kExprF32Ne, kWasmF32, kWasmF32>(),
+        op<kExprF32Lt, kWasmF32, kWasmF32>(),
+        op<kExprF32Ge, kWasmF32, kWasmF32>(),
+
+        op<kExprF64Eq, kWasmF64, kWasmF64>(),
+        op<kExprF64Ne, kWasmF64, kWasmF64>(),
+        op<kExprF64Lt, kWasmF64, kWasmF64>(),
+        op<kExprF64Ge, kWasmF64, kWasmF64>(),
+
+        op<kExprI32Add, kWasmI32, kWasmI32>(),
+        op<kExprI32Sub, kWasmI32, kWasmI32>(),
+        op<kExprI32Mul, kWasmI32, kWasmI32>(),
+
+        op<kExprI32DivS, kWasmI32, kWasmI32>(),
+        op<kExprI32DivU, kWasmI32, kWasmI32>(),
+        op<kExprI32RemS, kWasmI32, kWasmI32>(),
+        op<kExprI32RemU, kWasmI32, kWasmI32>(),
+
+        op<kExprI32And, kWasmI32, kWasmI32>(),
+        op<kExprI32Ior, kWasmI32, kWasmI32>(),
+        op<kExprI32Xor, kWasmI32, kWasmI32>(),
+        op<kExprI32Shl, kWasmI32, kWasmI32>(),
+        op<kExprI32ShrU, kWasmI32, kWasmI32>(),
+        op<kExprI32ShrS, kWasmI32, kWasmI32>(),
+        op<kExprI32Ror, kWasmI32, kWasmI32>(),
+        op<kExprI32Rol, kWasmI32, kWasmI32>(),
+
+        op<kExprI32Clz, kWasmI32>(),  //
+        op<kExprI32Ctz, kWasmI32>(),  //
+        op<kExprI32Popcnt, kWasmI32>(),
+
+        op<kExprI32ConvertI64, kWasmI64>(),  //
+        op<kExprI32SConvertF32, kWasmF32>(),
+        op<kExprI32UConvertF32, kWasmF32>(),
+        op<kExprI32SConvertF64, kWasmF64>(),
+        op<kExprI32UConvertF64, kWasmF64>(),
+        op<kExprI32ReinterpretF32, kWasmF32>(),
+
+        block<kWasmI32>(),
+        block_br<kWasmI32>()};
+
+    static_assert(arraysize(alternates) < std::numeric_limits<uint8_t>::max(),
+                  "Too many alternates. Replace with a bigger type if needed.");
+    const auto which = data.get<uint8_t>();
+
+    alternates[which % arraysize(alternates)](data);
+  }
+}
+
+template <>
+void WasmGenerator::Generate<kWasmI64>(DataRange data) {
+  if (data.size() <= sizeof(uint64_t)) {
+    const uint8_t bytes[] = {WASM_I64V(data.get<uint64_t>())};
+    builder_->EmitCode(bytes, arraysize(bytes));
+  } else {
+    const std::function<void(DataRange)> alternates[] = {
+        op<kExprI64Add, kWasmI64, kWasmI64>(),
+        op<kExprI64Sub, kWasmI64, kWasmI64>(),
+        op<kExprI64Mul, kWasmI64, kWasmI64>(),
+
+        op<kExprI64DivS, kWasmI64, kWasmI64>(),
+        op<kExprI64DivU, kWasmI64, kWasmI64>(),
+        op<kExprI64RemS, kWasmI64, kWasmI64>(),
+        op<kExprI64RemU, kWasmI64, kWasmI64>(),
+
+        op<kExprI64And, kWasmI64, kWasmI64>(),
+        op<kExprI64Ior, kWasmI64, kWasmI64>(),
+        op<kExprI64Xor, kWasmI64, kWasmI64>(),
+        op<kExprI64Shl, kWasmI64, kWasmI64>(),
+        op<kExprI64ShrU, kWasmI64, kWasmI64>(),
+        op<kExprI64ShrS, kWasmI64, kWasmI64>(),
+        op<kExprI64Ror, kWasmI64, kWasmI64>(),
+        op<kExprI64Rol, kWasmI64, kWasmI64>(),
+
+        op<kExprI64Clz, kWasmI64>(),
+        op<kExprI64Ctz, kWasmI64>(),
+        op<kExprI64Popcnt, kWasmI64>(),
+
+        block<kWasmI64>(),
+        block_br<kWasmI64>()};
+
+    static_assert(arraysize(alternates) < std::numeric_limits<uint8_t>::max(),
+                  "Too many alternates. Replace with a bigger type if needed.");
+    const auto which = data.get<uint8_t>();
+
+    alternates[which % arraysize(alternates)](data);
+  }
+}
+
+template <>
+void WasmGenerator::Generate<kWasmF32>(DataRange data) {
+  if (data.size() <= sizeof(uint32_t)) {
+    const uint32_t i = data.get<uint32_t>();
+    builder_->Emit(kExprF32Const);
+    builder_->EmitCode(reinterpret_cast<const uint8_t*>(&i), sizeof(i));
+  } else {
+    const std::function<void(DataRange)> alternates[] = {
+        op<kExprF32Add, kWasmF32, kWasmF32>(),
+        op<kExprF32Sub, kWasmF32, kWasmF32>(),
+        op<kExprF32Mul, kWasmF32, kWasmF32>(),
+
+        block<kWasmF32>(), block_br<kWasmF32>()};
+
+    static_assert(arraysize(alternates) < std::numeric_limits<uint8_t>::max(),
+                  "Too many alternates. Replace with a bigger type if needed.");
+    const auto which = data.get<uint8_t>();
+
+    alternates[which % arraysize(alternates)](data);
+  }
+}
+
+template <>
+void WasmGenerator::Generate<kWasmF64>(DataRange data) {
+  if (data.size() <= sizeof(uint64_t)) {
+    // TODO (eholk): generate full 64-bit constants
+    uint64_t i = 0;
+    while (data.size() > 0) {
+      i <<= 8;
+      i |= data.get<uint8_t>();
+    }
+    builder_->Emit(kExprF64Const);
+    builder_->EmitCode(reinterpret_cast<uint8_t*>(&i), sizeof(i));
+  } else {
+    const std::function<void(DataRange)> alternates[] = {
+        op<kExprF64Add, kWasmF64, kWasmF64>(),
+        op<kExprF64Sub, kWasmF64, kWasmF64>(),
+        op<kExprF64Mul, kWasmF64, kWasmF64>(),
+
+        block<kWasmF64>(), block_br<kWasmF64>()};
+
+    static_assert(arraysize(alternates) < std::numeric_limits<uint8_t>::max(),
+                  "Too many alternates. Replace with a bigger type if needed.");
+    const auto which = data.get<uint8_t>();
+
+    alternates[which % arraysize(alternates)](data);
+  }
+}
+
+void WasmGenerator::Generate(ValueType type, DataRange data) {
+  switch (type) {
+    case kWasmI32:
+      return Generate<kWasmI32>(data);
+    case kWasmI64:
+      return Generate<kWasmI64>(data);
+    case kWasmF32:
+      return Generate<kWasmF32>(data);
+    case kWasmF64:
+      return Generate<kWasmF64>(data);
+    default:
+      UNREACHABLE();
+  }
+}
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  // Save the flag so that we can change it and restore it later.
+  bool generate_test = v8::internal::FLAG_wasm_code_fuzzer_gen_test;
+  if (generate_test) {
+    v8::internal::OFStream os(stdout);
+
+    os << "// Copyright 2017 the V8 project authors. All rights reserved."
+       << std::endl;
+    os << "// Use of this source code is governed by a BSD-style license that "
+          "can be"
+       << std::endl;
+    os << "// found in the LICENSE file." << std::endl;
+    os << std::endl;
+    os << "load(\"test/mjsunit/wasm/wasm-constants.js\");" << std::endl;
+    os << "load(\"test/mjsunit/wasm/wasm-module-builder.js\");" << std::endl;
+    os << std::endl;
+    os << "(function() {" << std::endl;
+    os << "  var builder = new WasmModuleBuilder();" << std::endl;
+    os << "  builder.addMemory(16, 32, false);" << std::endl;
+    os << "  builder.addFunction(\"test\", kSig_i_iii)" << std::endl;
+    os << "    .addBodyWithEnd([" << std::endl;
+  }
+  v8_fuzzer::FuzzerSupport* support = v8_fuzzer::FuzzerSupport::Get();
+  v8::Isolate* isolate = support->GetIsolate();
+  v8::internal::Isolate* i_isolate =
+      reinterpret_cast<v8::internal::Isolate*>(isolate);
+
+  // Clear any pending exceptions from a prior run.
+  if (i_isolate->has_pending_exception()) {
+    i_isolate->clear_pending_exception();
+  }
+
+  v8::Isolate::Scope isolate_scope(isolate);
+  v8::HandleScope handle_scope(isolate);
+  v8::Context::Scope context_scope(support->GetContext());
+  v8::TryCatch try_catch(isolate);
+
+  v8::internal::AccountingAllocator allocator;
+  v8::internal::Zone zone(&allocator, ZONE_NAME);
+
+  TestSignatures sigs;
+
+  WasmModuleBuilder builder(&zone);
+
+  v8::internal::wasm::WasmFunctionBuilder* f =
+      builder.AddFunction(sigs.i_iii());
+
+  WasmGenerator gen(f);
+  gen.Generate<kWasmI32>(DataRange(data, static_cast<uint32_t>(size)));
+
+  uint8_t end_opcode = kExprEnd;
+  f->EmitCode(&end_opcode, 1);
+  f->ExportAs(v8::internal::CStrVector("main"));
+
+  ZoneBuffer buffer(&zone);
+  builder.WriteTo(buffer);
+
+  v8::internal::wasm::testing::SetupIsolateForWasmModule(i_isolate);
+
+  v8::internal::HandleScope scope(i_isolate);
+
+  ErrorThrower interpreter_thrower(i_isolate, "Interpreter");
+  std::unique_ptr<const WasmModule> module(testing::DecodeWasmModuleForTesting(
+      i_isolate, &interpreter_thrower, buffer.begin(), buffer.end(),
+      v8::internal::wasm::ModuleOrigin::kWasmOrigin, true));
+
+  // Clear the flag so that the WebAssembly code is not printed twice.
+  v8::internal::FLAG_wasm_code_fuzzer_gen_test = false;
+  if (module == nullptr) {
+    if (generate_test) {
+      v8::internal::OFStream os(stdout);
+      os << "            ])" << std::endl;
+      os << "            .exportFunc();" << std::endl;
+      os << "  assertThrows(function() { builder.instantiate(); });"
+         << std::endl;
+      os << "})();" << std::endl;
+    }
+    return 0;
+  }
+  if (generate_test) {
+    v8::internal::OFStream os(stdout);
+    os << "            ])" << std::endl;
+    os << "            .exportFunc();" << std::endl;
+    os << "  var module = builder.instantiate();" << std::endl;
+    os << "  module.exports.test(1, 2, 3);" << std::endl;
+    os << "})();" << std::endl;
+  }
+
+  ModuleWireBytes wire_bytes(buffer.begin(), buffer.end());
+  int32_t result_interpreted;
+  bool possible_nondeterminism = false;
+  {
+    WasmVal args[] = {WasmVal(1), WasmVal(2), WasmVal(3)};
+    result_interpreted = testing::InterpretWasmModule(
+        i_isolate, &interpreter_thrower, module.get(), wire_bytes, 0, args,
+        &possible_nondeterminism);
+  }
+
+  ErrorThrower compiler_thrower(i_isolate, "Compiler");
+  v8::internal::Handle<v8::internal::JSObject> instance =
+      testing::InstantiateModuleForTesting(i_isolate, &compiler_thrower,
+                                           module.get(), wire_bytes);
+  // Restore the flag.
+  v8::internal::FLAG_wasm_code_fuzzer_gen_test = generate_test;
+  if (!interpreter_thrower.error()) {
+    CHECK(!instance.is_null());
+  } else {
+    return 0;
+  }
+  int32_t result_compiled;
+  {
+    v8::internal::Handle<v8::internal::Object> arguments[] = {
+        v8::internal::handle(v8::internal::Smi::FromInt(1), i_isolate),
+        v8::internal::handle(v8::internal::Smi::FromInt(2), i_isolate),
+        v8::internal::handle(v8::internal::Smi::FromInt(3), i_isolate)};
+    result_compiled = testing::CallWasmFunctionForTesting(
+        i_isolate, instance, &compiler_thrower, "main", arraysize(arguments),
+        arguments, v8::internal::wasm::ModuleOrigin::kWasmOrigin);
+  }
+  if (result_interpreted == bit_cast<int32_t>(0xdeadbeef) &&
+      !possible_nondeterminism) {
+    CHECK(i_isolate->has_pending_exception());
+    i_isolate->clear_pending_exception();
+  } else {
+    // The WebAssembly spec allows the sign bit of NaN to be non-deterministic.
+    // This sign bit may cause result_interpreted to be different than
+    // result_compiled. Therefore we do not check the equality of the results
+    // if the execution may have produced a NaN at some point.
+    if (!possible_nondeterminism && (result_interpreted != result_compiled)) {
+      printf("\nInterpreter returned 0x%x but compiled code returned 0x%x\n",
+             result_interpreted, result_compiled);
+      V8_Fatal(__FILE__, __LINE__, "WasmCodeFuzzerHash=%x",
+               v8::internal::StringHasher::HashSequentialString(
+                   data, static_cast<int>(size), WASM_CODE_FUZZER_HASH_SEED));
+    }
+  }
+  return 0;
+}