🍒 [lldb] Cherry pick patches for MultiMemoryRead packet p2 (6.2)

lldb/include/lldb/Target/Process.h

@@ -1574,6 +1574,28 @@ class Process : public std::enable_shared_from_this<Process>,
   virtual size_t ReadMemory(lldb::addr_t vm_addr, void *buf, size_t size,
                             Status &error);
 
+  /// Read from multiple memory ranges and write the results into buffer.
+  /// This calls ReadMemoryFromInferior multiple times, once per range,
+  /// bypassing the read cache. Process implementations that can perform this
+  /// operation more efficiently should override this.
+  ///
+  /// \param[in] ranges
+  ///     A collection of ranges (base address + size) to read from.
+  ///
+  /// \param[out] buffer
+  ///     A buffer where the read memory will be written to. It must be at least
+  ///     as long as the sum of the sizes of each range.
+  ///
+  /// \return
+  ///     A vector of MutableArrayRef, where each MutableArrayRef is a slice of
+  ///     the input buffer into which the memory contents were copied. The size
+  ///     of the slice indicates how many bytes were read successfully. Partial
+  ///     reads are always performed from the start of the requested range,
+  ///     never from the middle or end.
+  virtual llvm::SmallVector<llvm::MutableArrayRef<uint8_t>>
+  ReadMemoryRanges(llvm::ArrayRef<Range<lldb::addr_t, size_t>> ranges,
+                   llvm::MutableArrayRef<uint8_t> buffer);
+
   /// Read of memory from a process.
   ///
   /// This function has the same semantics of ReadMemory except that it
@@ -1647,11 +1669,24 @@ class Process : public std::enable_shared_from_this<Process>,
                                          size_t byte_size, uint64_t fail_value,
                                          Status &error);
 
+  /// Use Process::ReadMemoryRanges to efficiently read multiple unsigned
+  /// integers from memory at once.
+  /// TODO: this should be upstream once there is a use for it there.
+  llvm::SmallVector<std::optional<uint64_t>>
+  ReadUnsignedIntegersFromMemory(llvm::ArrayRef<lldb::addr_t> addresses,
+                                 unsigned byte_size);
+
   int64_t ReadSignedIntegerFromMemory(lldb::addr_t load_addr, size_t byte_size,
                                       int64_t fail_value, Status &error);
 
   lldb::addr_t ReadPointerFromMemory(lldb::addr_t vm_addr, Status &error);
 
+  /// Use Process::ReadMemoryRanges to efficiently read multiple pointers from
+  /// memory at once.
+  /// TODO: this should be upstream once there is a use for it there.
+  llvm::SmallVector<std::optional<lldb::addr_t>>
+  ReadPointersFromMemory(llvm::ArrayRef<lldb::addr_t> ptr_locs);
+
   bool WritePointerToMemory(lldb::addr_t vm_addr, lldb::addr_t ptr_value,
                             Status &error);
 

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp

@@ -279,22 +279,23 @@ ClassDescriptorV2::ReadMethods(llvm::ArrayRef<lldb::addr_t> addresses,
   const size_t num_methods = addresses.size();
 
   llvm::SmallVector<uint8_t, 0> buffer(num_methods * size, 0);
-  llvm::DenseSet<uint32_t> failed_indices;
 
-  for (auto [idx, addr] : llvm::enumerate(addresses)) {
-    Status error;
-    process->ReadMemory(addr, buffer.data() + idx * size, size, error);
-    if (error.Fail())
-      failed_indices.insert(idx);
-  }
+  llvm::SmallVector<Range<addr_t, size_t>> mem_ranges =
+      llvm::to_vector(llvm::map_range(llvm::seq(num_methods), [&](size_t idx) {
+        return Range<addr_t, size_t>(addresses[idx], size);
+      }));
+
+  llvm::SmallVector<llvm::MutableArrayRef<uint8_t>> read_results =
+      process->ReadMemoryRanges(mem_ranges, buffer);
 
   llvm::SmallVector<method_t, 0> methods;
   methods.reserve(num_methods);
-  for (auto [idx, addr] : llvm::enumerate(addresses)) {
-    if (failed_indices.contains(idx))
+  for (auto [addr, memory] : llvm::zip(addresses, read_results)) {
+    // Ignore partial reads.
+    if (memory.size() != size)
       continue;
-    DataExtractor extractor(buffer.data() + idx * size, size,
-                            process->GetByteOrder(),
+
+    DataExtractor extractor(memory.data(), size, process->GetByteOrder(),
                             process->GetAddressByteSize());
     methods.push_back(method_t());
     methods.back().Read(extractor, process, addr, relative_selector_base_addr,

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp

@@ -2337,14 +2337,15 @@ class CommandObjectLanguageSwiftTaskInfo final : public CommandObjectParsed {
       }
 
       TaskInspector task_inspector;
-      auto task_addr_or_err = task_inspector.GetTaskAddrFromThreadLocalStorage(
-          m_exe_ctx.GetThreadRef());
-      if (auto error = task_addr_or_err.takeError()) {
-        result.AppendError(toString(std::move(error)));
+      std::optional<lldb::addr_t> maybe_task_addr =
+          task_inspector.GetTaskAddrFromThreadLocalStorage(
+              m_exe_ctx.GetThreadRef());
+      if (!task_addr) {
+        result.AppendError("could find the task address");
         return;
       }
 
-      task_addr = task_addr_or_err.get();
+      task_addr = *maybe_task_addr;
     }
 
     auto ts_or_err = m_exe_ctx.GetTargetRef().GetScratchTypeSystemForLanguage(
@@ -2935,19 +2936,6 @@ std::optional<lldb::addr_t> SwiftLanguageRuntime::TrySkipVirtualParentProlog(
   return pc_value;
 }
 
-/// Attempts to read the memory location at `task_addr_location`, producing
-/// the Task pointer if possible.
-static llvm::Expected<lldb::addr_t>
-ReadTaskAddr(lldb::addr_t task_addr_location, Process &process) {
-  Status status;
-  addr_t task_addr = process.ReadPointerFromMemory(task_addr_location, status);
-  if (status.Fail())
-    return llvm::joinErrors(
-        llvm::createStringError("could not get current task from thread"),
-        status.takeError());
-  return task_addr;
-}
-
 /// Compute the location where the Task pointer for `real_thread` is stored by
 /// the runtime.
 static llvm::Expected<lldb::addr_t>
@@ -2975,48 +2963,146 @@ ComputeTaskAddrLocationFromThreadLocalStorage(Thread &real_thread) {
 #endif
 }
 
-llvm::Expected<lldb::addr_t>
+/// Helper function to read all `pointers` from process memory at once.
+/// Consumes any errors from the input by propagating them to the output.
+static llvm::SmallVector<std::optional<addr_t>>
+MultiReadPointers(Process &process,
+                  llvm::MutableArrayRef<std::optional<addr_t>> maybe_pointers) {
+  llvm::SmallVector<std::optional<addr_t>> final_results;
+  llvm::SmallVector<addr_t> to_read;
+  final_results.reserve(maybe_pointers.size());
+  to_read.reserve(maybe_pointers.size());
+
+  /// Filter the input: propagate input errors directly to the output, forward
+  /// proper inputs to `to_read`.
+  for (std::optional<addr_t> &maybe_ptr : maybe_pointers) {
+    if (!maybe_ptr)
+      final_results.emplace_back(std::nullopt);
+    else {
+      final_results.push_back(LLDB_INVALID_ADDRESS);
+      to_read.push_back(*maybe_ptr);
+    }
+  }
+
+  llvm::SmallVector<std::optional<addr_t>> read_results =
+      process.ReadPointersFromMemory(to_read);
+  llvm::MutableArrayRef<std::optional<addr_t>> results_ref = read_results;
+
+  // Move the results in the slots not filled by errors from the input.
+  for (std::optional<addr_t> &maybe_result : final_results)
+    if (maybe_result) {
+      maybe_result = results_ref.front();
+      results_ref = results_ref.drop_front();
+    }
+
+  assert(results_ref.empty());
+  return final_results;
+}
+
+/// Helper function to read `addr` from process memory. Errors in the input are
+/// propagated to to the output.
+static std::optional<addr_t> ReadPointer(Process &process,
+                                         std::optional<addr_t> addr) {
+  return MultiReadPointers(process, addr)[0];
+}
+
+std::optional<lldb::addr_t>
 TaskInspector::GetTaskAddrFromThreadLocalStorage(Thread &thread) {
-  // Look through backing threads when inspecting TLS.
-  Thread &real_thread =
-      thread.GetBackingThread() ? *thread.GetBackingThread() : thread;
+  return GetTaskAddrFromThreadLocalStorage(&thread)[0];
+}
 
-  if (auto it = m_tid_to_task_addr_location.find(real_thread.GetID());
-      it != m_tid_to_task_addr_location.end()) {
+llvm::SmallVector<std::optional<lldb::addr_t>>
+TaskInspector::GetTaskAddrLocations(llvm::ArrayRef<Thread *> threads) {
+  llvm::SmallVector<std::optional<addr_t>> addr_locations;
+  addr_locations.reserve(threads.size());
+
+  for (auto [idx, thread] : llvm::enumerate(threads)) {
+    Thread &real_thread =
+        thread->GetBackingThread() ? *thread->GetBackingThread() : *thread;
+
+    auto it = m_tid_to_task_addr_location.find(real_thread.GetID());
+    if (it != m_tid_to_task_addr_location.end()) {
+      addr_locations.push_back(it->second);
 #ifndef NDEBUG
-    // In assert builds, check that caching did not produce incorrect results.
-    llvm::Expected<lldb::addr_t> task_addr_location =
-        ComputeTaskAddrLocationFromThreadLocalStorage(real_thread);
-    assert(task_addr_location);
-    assert(it->second == *task_addr_location);
+      // In assert builds, check that caching did not produce incorrect results.
+      llvm::Expected<lldb::addr_t> task_addr_location =
+          ComputeTaskAddrLocationFromThreadLocalStorage(real_thread);
+      assert(task_addr_location);
+      assert(it->second == *task_addr_location);
 #endif
-    llvm::Expected<lldb::addr_t> task_addr =
-        ReadTaskAddr(it->second, *thread.GetProcess());
-    if (task_addr)
-      return task_addr;
-    // If the cached task addr location became invalid, invalidate the cache.
-    m_tid_to_task_addr_location.erase(it);
-    LLDB_LOG_ERROR(GetLog(LLDBLog::OS), task_addr.takeError(),
-                   "TaskInspector: evicted task location address due to "
-                   "invalid memory read: {0}");
-  }
-
-  llvm::Expected<lldb::addr_t> task_addr_location =
+      continue;
+    }
+    llvm::Expected<addr_t> addr_loc =
+        ComputeTaskAddrLocationFromThreadLocalStorage(real_thread);
+    if (!addr_loc) {
+      LLDB_LOG_ERROR(GetLog(LLDBLog::OS), addr_loc.takeError(),
+                     "TaskInspector: failed to compute task address location "
+                     "from TLS: {0}");
+      addr_locations.push_back(std::nullopt);
+    } else
+      addr_locations.push_back(*addr_loc);
+  }
+  return addr_locations;
+}
+
+std::optional<addr_t> TaskInspector::RetryRead(Thread &thread,
+                                               addr_t task_addr_location) {
+  Thread &real_thread =
+      thread.GetBackingThread() ? *thread.GetBackingThread() : thread;
+  user_id_t tid = real_thread.GetID();
+
+  // For unsuccessful reads whose address was not cached, don't try again.
+  if (!m_tid_to_task_addr_location.erase(tid))
+    return std::nullopt;
+
+  LLDB_LOG(GetLog(LLDBLog::OS), "TaskInspector: evicted task location "
+                                "address due to invalid memory read");
+
+  // The cached address could not be loaded. "This should never happen", but
+  // recompute the address and try again for completeness.
+  llvm::Expected<addr_t> task_addr_loc =
       ComputeTaskAddrLocationFromThreadLocalStorage(real_thread);
-  if (!task_addr_location)
-    return task_addr_location;
-
-  llvm::Expected<lldb::addr_t> task_addr =
-      ReadTaskAddr(*task_addr_location, *thread.GetProcess());
-
-  // If the read from this TLS address is successful, cache the TLS address.
-  // Caching without a valid read is dangerous: earlier in the thread
-  // lifetime, the result of GetExtendedInfo can be invalid.
-  if (task_addr &&
-      real_thread.GetProcess()->GetTarget().GetSwiftCacheTaskPointerLocation())
-    m_tid_to_task_addr_location.try_emplace(real_thread.GetID(),
-                                            *task_addr_location);
-  return task_addr;
+  if (!task_addr_loc) {
+    LLDB_LOG_ERROR(GetLog(LLDBLog::OS), task_addr_loc.takeError(),
+                   "TaskInspector: failed to compute task address location "
+                   "from TLS: {0}");
+    return std::nullopt;
+  }
+
+  std::optional<addr_t> read_retry_result =
+      ReadPointer(*thread.GetProcess(), *task_addr_loc);
+  if (read_retry_result)
+    m_tid_to_task_addr_location[tid] = *task_addr_loc;
+  return read_retry_result;
+}
+
+llvm::SmallVector<std::optional<addr_t>>
+TaskInspector::GetTaskAddrFromThreadLocalStorage(
+    llvm::ArrayRef<Thread *> threads) {
+  if (threads.empty())
+    return {};
+
+  llvm::SmallVector<std::optional<addr_t>> addr_locations =
+      GetTaskAddrLocations(threads);
+
+  Process &process = *threads[0]->GetProcess();
+  llvm::SmallVector<std::optional<addr_t>> mem_read_results =
+      MultiReadPointers(process, addr_locations);
+
+  for (auto [idx, thread] : llvm::enumerate(threads)) {
+    if (!addr_locations[idx])
+      continue;
+    // If the read was successful, cache the address.
+    if (mem_read_results[idx]) {
+      Thread &real_thread =
+          thread->GetBackingThread() ? *thread->GetBackingThread() : *thread;
+      m_tid_to_task_addr_location[real_thread.GetID()] = *addr_locations[idx];
+      continue;
+    }
+    mem_read_results[idx] = RetryRead(*thread, *addr_locations[idx]);
+  }
+
+  return mem_read_results;
 }
 
 namespace {

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.h

@@ -934,10 +934,24 @@ class TaskInspector {
 public:
   /// Inspects thread local storage to find the address of the currently
   /// executing task, if any.
-  llvm::Expected<lldb::addr_t>
-  GetTaskAddrFromThreadLocalStorage(Thread &thread);
+  std::optional<lldb::addr_t> GetTaskAddrFromThreadLocalStorage(Thread &thread);
+
+  /// Inspects thread local storage to find the address of the currently
+  /// executing task, if any.
+  llvm::SmallVector<std::optional<lldb::addr_t>>
+  GetTaskAddrFromThreadLocalStorage(llvm::ArrayRef<Thread *> threads);
 
 private:
+  /// For each thread in `threads`, return the location of the its task
+  /// pointer, if it exists.
+  llvm::SmallVector<std::optional<lldb::addr_t>>
+  GetTaskAddrLocations(llvm::ArrayRef<Thread *> threads);
+
+  /// If reading from a cached task address location failed, invalidate the
+  /// cache and try again.
+  std::optional<lldb::addr_t> RetryRead(Thread &thread,
+                                        lldb::addr_t task_addr_location);
+
   llvm::DenseMap<uint64_t, lldb::addr_t> m_tid_to_task_addr_location;
 };