libBacktraceOffline: improve unwinding callchains.

1. Extend MAX_BACKTRACE_FRAMES to 256, as we can have callchains
   with length near 256 when recording Android applications.

2. .eh_frame and .ARM.exidx doesn't know how to unwind from instructions
   setting up or destroying stack frames. It can lead to wrong callchains,
   which may contain pcs outside executable mapping areas. Stop unwinding
   once this is detected.

3. Some CIE entries in .eh_frame/.debug_frame suggest unwinder reading
   personality routine from memory. However, that is not available in
   offline unwinding, and leads to ACCESS_MEM_FAILED error. Work around
   this by returning all zero data when failed to read data for some
   addresses.

4. Some libraries have empty .eh_frame_hdr but valid .eh_frame.
   Work around this by building eh_frame_hdr manually.

5. Prefer to use .debug_frame than .eh_frame. Because the former
   can unwind instructions setting up and destroying stack frames.

Bug: http://b/69383534
Test: run backtrace_test.
Test: run simpleperf on some apps.

Change-Id: I62dddda3865dd567c6be150ce5527dc2d3516256

0 files changed, 0 insertions, 0 deletions