src: add debugging array allocator

Add a subclass of `ArrayBufferAllocator` that performs additional
debug checking, which in particular verifies that:

- All `ArrayBuffer` backing stores have been allocated with this
  allocator, or have been explicitly marked as coming from a
  compatible source.
- All memory allocated by the allocator has been freed once it is
  destroyed.

PR-URL: nodejs#26207
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>

src/api/environment.cc

@@ -75,8 +75,82 @@ void* ArrayBufferAllocator::Allocate(size_t size) {
     return UncheckedMalloc(size);
 }
 
+DebuggingArrayBufferAllocator::~DebuggingArrayBufferAllocator() {
+  CHECK(allocations_.empty());
+}
+
+void* DebuggingArrayBufferAllocator::Allocate(size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  void* data = ArrayBufferAllocator::Allocate(size);
+  RegisterPointerInternal(data, size);
+  return data;
+}
+
+void* DebuggingArrayBufferAllocator::AllocateUninitialized(size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  void* data = ArrayBufferAllocator::AllocateUninitialized(size);
+  RegisterPointerInternal(data, size);
+  return data;
+}
+
+void DebuggingArrayBufferAllocator::Free(void* data, size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  UnregisterPointerInternal(data, size);
+  ArrayBufferAllocator::Free(data, size);
+}
+
+void* DebuggingArrayBufferAllocator::Reallocate(void* data,
+                                                size_t old_size,
+                                                size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  void* ret = ArrayBufferAllocator::Reallocate(data, old_size, size);
+  if (ret == nullptr) {
+    if (size == 0)  // i.e. equivalent to free().
+      UnregisterPointerInternal(data, old_size);
+    return nullptr;
+  }
+
+  if (data != nullptr) {
+    auto it = allocations_.find(data);
+    CHECK_NE(it, allocations_.end());
+    allocations_.erase(it);
+  }
+
+  RegisterPointerInternal(ret, size);
+  return ret;
+}
+
+void DebuggingArrayBufferAllocator::RegisterPointer(void* data, size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  RegisterPointerInternal(data, size);
+}
+
+void DebuggingArrayBufferAllocator::UnregisterPointer(void* data, size_t size) {
+  Mutex::ScopedLock lock(mutex_);
+  UnregisterPointerInternal(data, size);
+}
+
+void DebuggingArrayBufferAllocator::UnregisterPointerInternal(void* data,
+                                                              size_t size) {
+  if (data == nullptr) return;
+  auto it = allocations_.find(data);
+  CHECK_NE(it, allocations_.end());
+  CHECK_EQ(it->second, size);
+  allocations_.erase(it);
+}
+
+void DebuggingArrayBufferAllocator::RegisterPointerInternal(void* data,
+                                                            size_t size) {
+  if (data == nullptr) return;
+  CHECK_EQ(allocations_.count(data), 0);
+  allocations_[data] = size;
+}
+
 ArrayBufferAllocator* CreateArrayBufferAllocator() {
-  return new ArrayBufferAllocator();
+  if (per_process::cli_options->debug_arraybuffer_allocations)
+    return new DebuggingArrayBufferAllocator();
+  else
+    return new ArrayBufferAllocator();
 }
 
 void FreeArrayBufferAllocator(ArrayBufferAllocator* allocator) {

src/node_internals.h

@@ -109,11 +109,34 @@ class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
   void* AllocateUninitialized(size_t size) override
     { return node::UncheckedMalloc(size); }
   void Free(void* data, size_t) override { free(data); }
+  virtual void* Reallocate(void* data, size_t old_size, size_t size) {
+    return static_cast<void*>(
+        UncheckedRealloc<char>(static_cast<char*>(data), size));
+  }
+  virtual void RegisterPointer(void* data, size_t size) {}
+  virtual void UnregisterPointer(void* data, size_t size) {}
 
  private:
   uint32_t zero_fill_field_ = 1;  // Boolean but exposed as uint32 to JS land.
 };
 
+class DebuggingArrayBufferAllocator final : public ArrayBufferAllocator {
+ public:
+  ~DebuggingArrayBufferAllocator() override;
+  void* Allocate(size_t size) override;
+  void* AllocateUninitialized(size_t size) override;
+  void Free(void* data, size_t size) override;
+  void* Reallocate(void* data, size_t old_size, size_t size) override;
+  void RegisterPointer(void* data, size_t size) override;
+  void UnregisterPointer(void* data, size_t size) override;
+
+ private:
+  void RegisterPointerInternal(void* data, size_t size);
+  void UnregisterPointerInternal(void* data, size_t size);
+  Mutex mutex_;
+  std::unordered_map<void*, size_t> allocations_;
+};
+
 namespace Buffer {
 v8::MaybeLocal<v8::Object> Copy(Environment* env, const char* data, size_t len);
 v8::MaybeLocal<v8::Object> New(Environment* env, size_t size);

src/node_options.cc

@@ -369,6 +369,10 @@ PerProcessOptionsParser::PerProcessOptionsParser() {
             "SlowBuffer instances",
             &PerProcessOptions::zero_fill_all_buffers,
             kAllowedInEnvironment);
+  AddOption("--debug-arraybuffer-allocations",
+            "", /* undocumented, only for debugging */
+            &PerProcessOptions::debug_arraybuffer_allocations,
+            kAllowedInEnvironment);
 
   AddOption("--security-reverts", "", &PerProcessOptions::security_reverts);
   AddOption("--completion-bash",

src/node_options.h

@@ -168,6 +168,7 @@ class PerProcessOptions : public Options {
   uint64_t max_http_header_size = 8 * 1024;
   int64_t v8_thread_pool_size = 4;
   bool zero_fill_all_buffers = false;
+  bool debug_arraybuffer_allocations = false;
 
   std::vector<std::string> security_reverts;
   bool print_bash_completion = false;