server: functional backtraces for OS X (#2549)

Description:
bombela/backward-cpp now has some support for backtraces on OS X. Bump backward-cpp to a revision that contains the change. Modify stack trace output on OS X since addr2line (via homebrew's binutils package) doesn't seem to be able to resolve addresses from the stack trace (or lldb for that matter). Instead, print as much information as possible directly in the stack trace (which is equivalent to lldb's output given bazelbuild/bazel#2537).

Risk Level: Low

Testing:
Manually tested stack traces by forcing division by zero.

Signed-off-by: Stephan Zuercher stephan@turbinelabs.io

bazel/repository_locations.bzl

@@ -4,7 +4,7 @@ REPOSITORY_LOCATIONS = dict(
         remote = "https://github.com/abseil/abseil-cpp",
     ),
     com_github_bombela_backward = dict(
-        commit = "cd1c4bd9e48afe812a0e996d335298c455afcd92",  # v1.3
+        commit = "44ae9609e860e3428cd057f7052e505b4819eb84",  # 2018-02-06
         remote = "https://github.com/bombela/backward-cpp",
     ),
     com_github_cyan4973_xxhash = dict(

source/server/backtrace.h

@@ -81,8 +81,14 @@ class BackwardsTrace : Logger::Loggable<Logger::Id::backtrace> {
     backward::ResolvedTrace first_frame_trace = resolver.resolve(stack_trace_[0]);
     auto obj_name = first_frame_trace.object_filename;
 
+#ifdef __APPLE__
+    // The stack_decode.py script uses addr2line which isn't readily available and doesn't seem to
+    // work when installed.
+    ENVOY_LOG(critical, "Backtrace obj<{}> thr<{}>:", obj_name, thread_id);
+#else
     ENVOY_LOG(critical, "Backtrace obj<{}> thr<{}> (use tools/stack_decode.py):", obj_name,
               thread_id);
+#endif
 
     // Backtrace gets tagged by ASAN when we try the object name resolution for the last
     // frame on stack, so skip the last one. It has no useful info anyway.
@@ -92,7 +98,14 @@ class BackwardsTrace : Logger::Loggable<Logger::Id::backtrace> {
         obj_name = trace.object_filename;
         ENVOY_LOG(critical, "thr<{}> obj<{}>", thread_id, obj_name);
       }
+
+#ifdef __APPLE__
+      // In the absence of stack_decode.py, print the function name.
+      ENVOY_LOG(critical, "thr<{}> #{} {}: {}", thread_id, stack_trace_[i].idx,
+                stack_trace_[i].addr, trace.object_function);
+#else
       ENVOY_LOG(critical, "thr<{}> #{} {}", thread_id, stack_trace_[i].idx, stack_trace_[i].addr);
+#endif
     }
     ENVOY_LOG(critical, "end backtrace thread {}", stack_trace_.thread_id());
   }