fuzzing test and detect the memmove error (#688)

* fuzzing

* add an additional random walk test

fuzzing/CMakeLists.txt

@@ -0,0 +1,22 @@
+include(FetchContent)
+
+FetchContent_Declare(
+  fuzztest
+  GIT_REPOSITORY https://github.com/google/fuzztest.git
+  GIT_TAG        2024-10-28
+)
+
+FetchContent_MakeAvailable(fuzztest)
+
+enable_testing()
+fuzztest_setup_fuzzing_flags()
+
+add_executable(
+  snmalloc-fuzzer
+  snmalloc-fuzzer.cpp
+)
+
+target_link_libraries(snmalloc-fuzzer PRIVATE snmalloc)
+target_compile_options(snmalloc-fuzzer PRIVATE -fsanitize=address -DADDRESS_SANITIZER)
+
+link_fuzztest(snmalloc-fuzzer)

fuzzing/snmalloc-fuzzer.cpp

@@ -0,0 +1,199 @@
+#include "fuzztest/fuzztest.h"
+#include "snmalloc/snmalloc.h"
+
+#include <cstddef>
+#include <cstdlib>
+#include <execution>
+#include <new>
+#include <string_view>
+#include <vector>
+
+void simple_memcpy(std::vector<char> data)
+{
+  std::vector<char> dest(data.size());
+  snmalloc::memcpy<true>(dest.data(), data.data(), data.size());
+  if (data != dest)
+    abort();
+}
+
+void memcpy_with_align_offset(
+  size_t source_alignment,
+  size_t source_offset,
+  size_t dest_alignment,
+  size_t dest_offset,
+  std::string data)
+{
+  source_alignment = 1 << source_alignment;
+  dest_alignment = 1 << dest_alignment;
+  source_offset = source_offset % source_alignment;
+  dest_offset = dest_offset % dest_alignment;
+  auto src_ = ::operator new(
+    data.size() + source_offset, std::align_val_t{source_alignment});
+  auto dst_ =
+    ::operator new(data.size() + dest_offset, std::align_val_t{dest_alignment});
+  auto src = static_cast<char*>(src_) + source_offset;
+  auto dst = static_cast<char*>(dst_) + dest_offset;
+  snmalloc::memcpy<true>(src, data.data(), data.size());
+  snmalloc::memcpy<true>(dst, src, data.size());
+  if (std::string_view(dst, data.size()) != data)
+    abort();
+  ::operator delete(src_, std::align_val_t{source_alignment});
+  ::operator delete(dst_, std::align_val_t{dest_alignment});
+}
+
+void simple_memmove(std::vector<char> data)
+{
+  std::vector<char> dest(data.size());
+  snmalloc::memmove<true>(dest.data(), data.data(), data.size());
+  if (data != dest)
+    abort();
+}
+
+void forward_memmove(std::string data, size_t offset)
+{
+  std::string to_move = data;
+  offset = std::min(offset, data.size());
+  snmalloc::memmove<true>(
+    to_move.data() + offset, to_move.data(), to_move.size() - offset);
+  size_t after_move = to_move.size() - offset;
+  if (
+    std::string_view(data.data(), after_move) !=
+    std::string_view(to_move.data() + offset, after_move))
+    abort();
+}
+
+void backward_memmove(std::string data, size_t offset)
+{
+  std::string to_move = data;
+  offset = std::min(offset, data.size());
+  snmalloc::memmove<true>(
+    to_move.data(), to_move.data() + offset, to_move.size() - offset);
+  size_t after_move = to_move.size() - offset;
+  if (
+    std::string_view(data.data() + offset, after_move) !=
+    std::string_view(to_move.data(), after_move))
+    abort();
+}
+
+constexpr static size_t size_limit = 16384;
+
+enum class EventKind : unsigned
+{
+  AllocZero = 0,
+  AllocNoZero = 1,
+  Free = 2,
+  Check = 3,
+  ReFill = 4,
+};
+
+struct Event
+{
+  EventKind kind;
+  size_t size_or_index;
+  char filler;
+
+  Event(std::tuple<unsigned, size_t, char> payload)
+  : kind(static_cast<EventKind>(std::get<0>(payload) % 5)),
+    size_or_index(std::get<1>(payload)),
+    filler(std::get<2>(payload))
+  {
+    if (kind == EventKind::AllocZero || kind == EventKind::AllocNoZero)
+    {
+      size_or_index %= size_limit;
+    }
+  }
+};
+
+struct Result
+{
+  char filler;
+  char* ptr;
+  size_t size;
+
+  void check()
+  {
+    auto res = std::reduce(
+      std::execution::unseq,
+      ptr,
+      ptr + size,
+      static_cast<unsigned char>(0),
+      [&](unsigned char acc, char c) -> unsigned char {
+        return acc | static_cast<unsigned char>(c != filler);
+      });
+    if (res)
+      abort();
+  }
+};
+
+void snmalloc_random_walk(
+  std::vector<std::tuple<unsigned, size_t, char>> payload)
+{
+  std::vector<Result> results;
+  for (auto& p : payload)
+  {
+    Event e(p);
+    auto scoped = snmalloc::get_scoped_allocator();
+    switch (e.kind)
+    {
+      case EventKind::AllocZero:
+      {
+        auto ptr =
+          static_cast<char*>(scoped->alloc<snmalloc::YesZero>(e.size_or_index));
+        results.push_back({0, ptr, e.size_or_index});
+        break;
+      }
+
+      case EventKind::AllocNoZero:
+      {
+        auto ptr =
+          static_cast<char*>(scoped->alloc<snmalloc::NoZero>(e.size_or_index));
+        std::fill(ptr, ptr + e.size_or_index, e.filler);
+        results.push_back({e.filler, ptr, e.size_or_index});
+        break;
+      }
+
+      case EventKind::Free:
+      {
+        if (results.empty())
+          break;
+        auto index = e.size_or_index % results.size();
+        scoped->dealloc(results[index].ptr);
+        results.erase(results.begin() + static_cast<ptrdiff_t>(index));
+        break;
+      }
+
+      case EventKind::Check:
+      {
+        for (auto& r : results)
+          r.check();
+        break;
+      }
+
+      case EventKind::ReFill:
+      {
+        if (results.empty())
+          break;
+        auto index = e.size_or_index % results.size();
+        std::fill(
+          results[index].ptr,
+          results[index].ptr + results[index].size,
+          e.filler);
+        results[index].filler = e.filler;
+        break;
+      }
+    }
+  }
+}
+
+FUZZ_TEST(snmalloc_fuzzing, simple_memcpy);
+FUZZ_TEST(snmalloc_fuzzing, simple_memmove);
+FUZZ_TEST(snmalloc_fuzzing, forward_memmove);
+FUZZ_TEST(snmalloc_fuzzing, backward_memmove);
+FUZZ_TEST(snmalloc_fuzzing, memcpy_with_align_offset)
+  .WithDomains(
+    fuzztest::InRange(0, 6),
+    fuzztest::Positive<size_t>(),
+    fuzztest::InRange(0, 6),
+    fuzztest::Positive<size_t>(),
+    fuzztest::String());
+FUZZ_TEST(snmalloc_fuzzing, snmalloc_random_walk);