Add a MemoryOfflineBuffer object.

Use this for offline stack data so that it's not necessary to
copy any data around.

Add unit tests for the new object.

Bug: 77258731
Bug: 74354410

Test: Ran libunwindstack/libbacktrace unit tests.
Change-Id: I9b0f25d9520c96e64aedef5f295423c60ddb3488

2 files changed, 9 insertions, 7 deletions

diff --git a/libbacktrace/UnwindStackMap.cpp b/libbacktrace/UnwindStackMap.cpp
index 9c6fed43c..d2d6ab8fa 100644
--- a/libbacktrace/UnwindStackMap.cpp
+++ b/libbacktrace/UnwindStackMap.cpp
@@ -149,13 +149,12 @@ bool UnwindStackOfflineMap::CreateProcessMemory(const backtrace_stackinfo_t& sta
   }
 
   // Create the process memory from the stack data.
-  uint64_t size = stack.end - stack.start;
-  unwindstack::MemoryBuffer* memory = new unwindstack::MemoryBuffer;
-  memory->Resize(size);
-  memcpy(memory->GetPtr(0), stack.data, size);
-  std::shared_ptr<unwindstack::Memory> shared_memory(memory);
-
-  process_memory_.reset(new unwindstack::MemoryRange(shared_memory, 0, size, stack.start));
+  if (memory_ == nullptr) {
+    memory_ = new unwindstack::MemoryOfflineBuffer(stack.data, stack.start, stack.end);
+    process_memory_.reset(memory_);
+  } else {
+    memory_->Reset(stack.data, stack.start, stack.end);
+  }
   return true;
 }
 
diff --git a/libbacktrace/UnwindStackMap.h b/libbacktrace/UnwindStackMap.h
index ec0d9c148..039f4a289 100644
--- a/libbacktrace/UnwindStackMap.h
+++ b/libbacktrace/UnwindStackMap.h
@@ -79,6 +79,9 @@ class UnwindStackOfflineMap : public UnwindStackMap {
   bool Build(const std::vector<backtrace_map_t>& maps);
 
   bool CreateProcessMemory(const backtrace_stackinfo_t& stack);
+
+ private:
+  unwindstack::MemoryOfflineBuffer* memory_ = nullptr;
 };
 
 #endif  // _LIBBACKTRACE_UNWINDSTACK_MAP_H