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
Merged-In: I3fb9b00c02d2cf2cc5911541bba0346c6f39b8e6
(cherry picked from commit d11ed86d65e870c5ea0d4918693376d474dbfe7d)
diff --git a/libunwindstack/Elf.cpp b/libunwindstack/Elf.cpp
index 4b93abb..3454913 100644
--- a/libunwindstack/Elf.cpp
+++ b/libunwindstack/Elf.cpp
@@ -160,7 +160,7 @@
   if (valid_) {
     return interface_->LastErrorCode();
   }
-  return ERROR_NONE;
+  return ERROR_INVALID_ELF;
 }
 
 uint64_t Elf::GetLastErrorAddress() {
@@ -170,22 +170,23 @@
   return 0;
 }
 
+// The relative pc expectd by this function is relative to the start of the elf.
+bool Elf::StepIfSignalHandler(uint64_t rel_pc, Regs* regs, Memory* process_memory) {
+  if (!valid_) {
+    return false;
+  }
+  return regs->StepIfSignalHandler(rel_pc, this, process_memory);
+}
+
 // The relative pc is always relative to the start of the map from which it comes.
-bool Elf::Step(uint64_t rel_pc, uint64_t adjusted_rel_pc, Regs* regs, Memory* process_memory,
-               bool* finished) {
+bool Elf::Step(uint64_t rel_pc, Regs* regs, Memory* process_memory, bool* finished) {
   if (!valid_) {
     return false;
   }
 
-  // The relative pc expectd by StepIfSignalHandler is relative to the start of the elf.
-  if (regs->StepIfSignalHandler(rel_pc, this, process_memory)) {
-    *finished = false;
-    return true;
-  }
-
   // Lock during the step which can update information in the object.
   std::lock_guard<std::mutex> guard(lock_);
-  return interface_->Step(adjusted_rel_pc, regs, process_memory, finished);
+  return interface_->Step(rel_pc, regs, process_memory, finished);
 }
 
 bool Elf::IsValidElf(Memory* memory) {