Fix pc/function name for signal handler frame.

This refactors the step function slightly to split it up into
distinct pieces since the code needs to handle a signal handler
versus normal step slightly differently.

Add a new error for an invalid elf.

Modify libbacktrace code to handle new error code.

Bug: 130302288

Test: libbacktrace/libunwindstack unit tests.
Change-Id: I3fb9b00c02d2cf2cc5911541bba0346c6f39b8e6
diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
index 6bec63c..71980d7 100644
--- a/libbacktrace/Backtrace.cpp
+++ b/libbacktrace/Backtrace.cpp
@@ -170,5 +170,7 @@
       return "Failed to unwind due to invalid unwind information";
     case BACKTRACE_UNWIND_ERROR_REPEATED_FRAME:
       return "Failed to unwind due to same sp/pc repeating";
+    case BACKTRACE_UNWIND_ERROR_INVALID_ELF:
+      return "Failed to unwind due to invalid elf";
   }
 }
diff --git a/libbacktrace/UnwindStack.cpp b/libbacktrace/UnwindStack.cpp
index f5f9b2a..36640cd 100644
--- a/libbacktrace/UnwindStack.cpp
+++ b/libbacktrace/UnwindStack.cpp
@@ -89,6 +89,10 @@
       case unwindstack::ERROR_REPEATED_FRAME:
         error->error_code = BACKTRACE_UNWIND_ERROR_REPEATED_FRAME;
         break;
+
+      case unwindstack::ERROR_INVALID_ELF:
+        error->error_code = BACKTRACE_UNWIND_ERROR_INVALID_ELF;
+        break;
     }
   }
 
diff --git a/libbacktrace/include/backtrace/Backtrace.h b/libbacktrace/include/backtrace/Backtrace.h
index 10e790b..404e7e8 100644
--- a/libbacktrace/include/backtrace/Backtrace.h
+++ b/libbacktrace/include/backtrace/Backtrace.h
@@ -64,6 +64,8 @@
   BACKTRACE_UNWIND_ERROR_UNWIND_INFO,
   // Unwind information stopped due to sp/pc repeating.
   BACKTRACE_UNWIND_ERROR_REPEATED_FRAME,
+  // Unwind information stopped due to invalid elf.
+  BACKTRACE_UNWIND_ERROR_INVALID_ELF,
 };
 
 struct BacktraceUnwindError {