Discards frames for code within library.

When doing a local unwind, do not include the frames that come
from either libunwind or libbacktrace.

Bug: 11518609
Change-Id: I0ec8d823aebbfa0903e61b16b7e5663f3fd65e78

4 files changed, 54 insertions, 17 deletions

diff --git a/libbacktrace/BacktraceCurrent.cpp b/libbacktrace/BacktraceCurrent.cpp
index b7190e256..fd1f4da7b 100644
--- a/libbacktrace/BacktraceCurrent.cpp
+++ b/libbacktrace/BacktraceCurrent.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#define _GNU_SOURCE 1
 #include <errno.h>
 #include <stdint.h>
 #include <string.h>
@@ -73,6 +74,16 @@ bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
   return UnwindFromContext(num_ignore_frames, nullptr);
 }
 
+bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) {
+  if (BacktraceMap::IsValid(frame.map)) {
+    const std::string library = basename(frame.map.name.c_str());
+    if (library == "libunwind.so" || library == "libbacktrace.so") {
+      return true;
+    }
+  }
+  return false;
+}
+
 static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static void SignalHandler(int, siginfo_t*, void* sigcontext) {
diff --git a/libbacktrace/BacktraceCurrent.h b/libbacktrace/BacktraceCurrent.h
index 81ea81d5a..8aad36d00 100644
--- a/libbacktrace/BacktraceCurrent.h
+++ b/libbacktrace/BacktraceCurrent.h
@@ -46,6 +46,9 @@ public:
 
   bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext) override;
 
+protected:
+  bool DiscardFrame(const backtrace_frame_data_t& frame);
+
 private:
   bool UnwindThread(size_t num_ignore_frames);
 
diff --git a/libbacktrace/UnwindCurrent.cpp b/libbacktrace/UnwindCurrent.cpp
index 12e289095..67e583f08 100644
--- a/libbacktrace/UnwindCurrent.cpp
+++ b/libbacktrace/UnwindCurrent.cpp
@@ -99,25 +99,30 @@ bool UnwindCurrent::UnwindFromContext(size_t num_ignore_frames, ucontext_t* ucon
       break;
     }
 
-    if (num_ignore_frames == 0) {
-      frames_.resize(num_frames+1);
-      backtrace_frame_data_t* frame = &frames_.at(num_frames);
-      frame->num = num_frames;
-      frame->pc = static_cast<uintptr_t>(pc);
-      frame->sp = static_cast<uintptr_t>(sp);
-      frame->stack_size = 0;
+    frames_.resize(num_frames+1);
+    backtrace_frame_data_t* frame = &frames_.at(num_frames);
+    frame->num = num_frames;
+    frame->pc = static_cast<uintptr_t>(pc);
+    frame->sp = static_cast<uintptr_t>(sp);
+    frame->stack_size = 0;
 
-      if (num_frames > 0) {
-        // Set the stack size for the previous frame.
-        backtrace_frame_data_t* prev = &frames_.at(num_frames-1);
-        prev->stack_size = frame->sp - prev->sp;
+    FillInMap(frame->pc, &frame->map);
+    // Check to see if we should skip this frame because it's coming
+    // from within the library, and we are doing a local unwind.
+    if (ucontext != nullptr || num_frames != 0 || !DiscardFrame(*frame)) {
+      if (num_ignore_frames == 0) {
+        // GetFunctionName is an expensive call, only do it if we are
+        // keeping the frame.
+        frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
+        if (num_frames > 0) {
+          // Set the stack size for the previous frame.
+          backtrace_frame_data_t* prev = &frames_.at(num_frames-1);
+          prev->stack_size = frame->sp - prev->sp;
+        }
+        num_frames++;
+      } else {
+        num_ignore_frames--;
       }
-
-      frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
-      FillInMap(frame->pc, &frame->map);
-      num_frames++;
-    } else {
-      num_ignore_frames--;
     }
     ret = unw_step (cursor.get());
   } while (ret > 0 && num_frames < MAX_BACKTRACE_FRAMES);
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index d40885647..5de80b1ac 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#define _GNU_SOURCE 1
 #include <dirent.h>
 #include <errno.h>
 #include <inttypes.h>
@@ -200,6 +201,23 @@ bool WaitForNonZero(int32_t* value, uint64_t seconds) {
   return false;
 }
 
+TEST(libbacktrace, local_no_unwind_frames) {
+  // Verify that a local unwind does not include any frames within
+  // libunwind or libbacktrace.
+  std::unique_ptr<Backtrace> backtrace(Backtrace::Create(getpid(), getpid()));
+  ASSERT_TRUE(backtrace->Unwind(0));
+
+  ASSERT_TRUE(backtrace->NumFrames() != 0);
+  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());
+    }
+    break;
+  }
+}
+
 TEST(libbacktrace, local_trace) {
   ASSERT_NE(test_level_one(1, 2, 3, 4, VerifyLevelBacktrace, nullptr), 0);
 }