commit c463ba45c42b4e2d8ce30c02a626d7183102f46e
author Christopher Ferris <cferris@google.com> Wed Mar 09 14:35:54 2016 -0800
committer Christopher Ferris <cferris@google.com> Thu Mar 10 14:14:43 2016 -0800
tree 4e68f1cb0a203371c57ef864def5acc4178a5d7f
parent 01d76eb1ecb943db042eb6618087c0e22588e6b3

Add error reporting mechanism for failing Unwind.

Remove the logging of an error if a thread disappears before the unwind
can begin. This can happen, so allow the caller to determine if this
is really a problem worth logging.

Bug: 27449879

(cherry picked from commit 206a3b9798e3622c906a3cafdb113c271c1c927c)

Change-Id: If9e7cfeb6eb7b122679a734c1a9eacee8354ef18

libbacktrace/UnwindPtrace.cpp

diff --git a/libbacktrace/UnwindPtrace.cpp b/libbacktrace/UnwindPtrace.cpp
index 07c2430..306d2ac 100644
--- a/libbacktrace/UnwindPtrace.cpp
+++ b/libbacktrace/UnwindPtrace.cpp
@@ -50,17 +50,22 @@
 bool UnwindPtrace::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
   if (GetMap() == nullptr) {
     // Without a map object, we can't do anything.
+    error_ = BACKTRACE_UNWIND_ERROR_MAP_MISSING;
     return false;
   }
 
+  error_ = BACKTRACE_UNWIND_NO_ERROR;
+
   if (ucontext) {
     BACK_LOGW("Unwinding from a specified context not supported yet.");
+    error_ = BACKTRACE_UNWIND_ERROR_UNSUPPORTED_OPERATION;
     return false;
   }
 
   addr_space_ = unw_create_addr_space(&_UPT_accessors, 0);
   if (!addr_space_) {
     BACK_LOGW("unw_create_addr_space failed.");
+    error_ = BACKTRACE_UNWIND_ERROR_SETUP_FAILED;
     return false;
   }
 
@@ -70,6 +75,7 @@
   upt_info_ = reinterpret_cast<struct UPT_info*>(_UPT_create(Tid()));
   if (!upt_info_) {
     BACK_LOGW("Failed to create upt info.");
+    error_ = BACKTRACE_UNWIND_ERROR_SETUP_FAILED;
     return false;
   }
 
@@ -77,6 +83,7 @@
   int ret = unw_init_remote(&cursor, addr_space_, upt_info_);
   if (ret < 0) {
     BACK_LOGW("unw_init_remote failed %d", ret);
+    error_ = BACKTRACE_UNWIND_ERROR_SETUP_FAILED;
     return false;
   }