Method to avoid skipping frames for local unwinds.

In cases where there might be a crash in the unwind library itself,
we need a method to avoid skipping these frames or we won't be able
to see the actual crash.

Added unit test for this behavior.

Bug: 74121887

Test: Ran unit tests on host and target.
Change-Id: I45825020c174016af39dd8ffdc67acb72a24ad4d
(cherry picked from commit 458f4e725d)

libbacktrace/UnwindStack.cpp

@@ -163,6 +163,9 @@ bool UnwindStackCurrent::UnwindFromContext(size_t num_ignore_frames, void* ucont
   }
 
   std::vector<std::string> skip_names{"libunwindstack.so", "libbacktrace.so"};
+  if (!skip_frames_) {
+    skip_names.clear();
+  }
   return Backtrace::Unwind(regs.get(), GetMap(), &frames_, num_ignore_frames, &skip_names, &error_);
 }
 

libbacktrace/backtrace_test.cpp

@@ -69,6 +69,9 @@
 // Number of simultaneous threads running in our forked process.
 #define NUM_PTRACE_THREADS 5
 
+// The list of shared libaries that make up the backtrace library.
+static std::vector<std::string> kBacktraceLibs{"libunwindstack.so", "libbacktrace.so"};
+
 struct thread_t {
   pid_t tid;
   int32_t state;
@@ -256,16 +259,49 @@ TEST(libbacktrace, local_no_unwind_frames) {
   VERIFY_NO_ERROR(backtrace->GetError().error_code);
 
   ASSERT_TRUE(backtrace->NumFrames() != 0);
+  // None of the frames should be in the backtrace libraries.
   for (const auto& frame : *backtrace ) {
     if (BacktraceMap::IsValid(frame.map)) {
       const std::string name = basename(frame.map.name.c_str());
-      ASSERT_TRUE(name != "libunwind.so" && name != "libbacktrace.so")
-        << DumpFrames(backtrace.get());
+      for (const auto& lib : kBacktraceLibs) {
+        ASSERT_TRUE(name != lib) << DumpFrames(backtrace.get());
+      }
     }
-    break;
   }
 }
 
+TEST(libbacktrace, local_unwind_frames) {
+  // Verify that a local unwind with the skip frames disabled does include
+  // frames within the backtrace libraries.
+  std::unique_ptr<Backtrace> backtrace(Backtrace::Create(getpid(), getpid()));
+  ASSERT_TRUE(backtrace.get() != nullptr);
+  backtrace->SetSkipFrames(false);
+  ASSERT_TRUE(backtrace->Unwind(0));
+  VERIFY_NO_ERROR(backtrace->GetError().error_code);
+
+  ASSERT_TRUE(backtrace->NumFrames() != 0);
+  size_t first_frame_non_backtrace_lib = 0;
+  for (const auto& frame : *backtrace) {
+    if (BacktraceMap::IsValid(frame.map)) {
+      const std::string name = basename(frame.map.name.c_str());
+      bool found = false;
+      for (const auto& lib : kBacktraceLibs) {
+        if (name == lib) {
+          found = true;
+          break;
+        }
+      }
+      if (!found) {
+        first_frame_non_backtrace_lib = frame.num;
+        break;
+      }
+    }
+  }
+
+  ASSERT_NE(0U, first_frame_non_backtrace_lib) << "No frames found in backtrace libraries:\n"
+                                               << DumpFrames(backtrace.get());
+}
+
 TEST(libbacktrace, local_trace) {
   ASSERT_NE(test_level_one(1, 2, 3, 4, VerifyLevelBacktrace, nullptr), 0);
 }

libbacktrace/include/backtrace/Backtrace.h

@@ -204,6 +204,9 @@ class Backtrace {
 
   std::string GetErrorString(BacktraceUnwindError error);
 
+  // Set whether to skip frames in libbacktrace/libunwindstack when doing a local unwind.
+  void SetSkipFrames(bool skip_frames) { skip_frames_ = skip_frames; }
+
  protected:
   Backtrace(pid_t pid, pid_t tid, BacktraceMap* map);
 
@@ -223,6 +226,9 @@ class Backtrace {
 
   std::vector<backtrace_frame_data_t> frames_;
 
+  // Skip frames in libbacktrace/libunwindstack when doing a local unwind.
+  bool skip_frames_ = true;
+
   BacktraceUnwindError error_;
 };