Small behavioral changes to the unwinder.

- Be a little more lenient when reading the cies/fdes. If next entry data
  winds up incorrect, don't fail, simply stop processing the entries. This
  only applies when reading all of the cies/fdes at once.
- Fail to init an eh_frame with no entries and fallback to assuming the
  eh_frame has no header instead.
- Change the step to always try debug_frame first which has the most
  accurate information.
- Add small unit tests and a couple of offline unit tests to verify
  this behavior.

These changes are needed to support offline unwinding since it depends
on this new behavior.

Bug: 65682279

Test: Ran new unit tests.
Change-Id: I3529f1b0c8e14cd7409494e5de2f3c9e78d0855e

1 files changed, 5 insertions, 0 deletions

diff --git a/libunwindstack/DwarfEhFrameWithHdr.cpp b/libunwindstack/DwarfEhFrameWithHdr.cpp
index 0337dba..e0f1eed 100644
--- a/libunwindstack/DwarfEhFrameWithHdr.cpp
+++ b/libunwindstack/DwarfEhFrameWithHdr.cpp
@@ -64,6 +64,11 @@ bool DwarfEhFrameWithHdr<AddressType>::Init(uint64_t offset, uint64_t size) {
     return false;
   }
 
+  if (fde_count_ == 0) {
+    last_error_ = DWARF_ERROR_NO_FDES;
+    return false;
+  }
+
   entries_offset_ = memory_.cur_offset();
   entries_end_ = offset + size;
   entries_data_offset_ = offset;