Update Go OS Plugin for newer runtimes

[labath]

source/Plugins/OperatingSystem/Go/OperatingSystemGo.cpp

253

To me, as someone who might accidentally wander into this part of codebase, a comment explaining that the symbols to look for differ between runtime versions would definitely be helpful.

[labath]

btw, this does not seem to follow lldb code style (braces on a new line), please reformat that.

[tberghammer]

Is it possible to query the version of the go runtime we are currently debugging and decide which symbol we look for instead of using this fallback mechanism? I think it would make the code easier to understand and also easier to add support for new runtime versions

[ribrdb]

I'm not sure how else we could identify the runtime version. I'm hoping to eventually add a producer string that has the version, but this would just be a git commit for development compilers.

[tberghammer]

A producer string would be excellent but I know it is not easy to add it to all part of the toolchain. In case of development compilers I would suggest to add the version number of the next or the previous iteration with some additional marking indicating that it is a development build so you can detect it from LLDB (e.g. 1.5+).

source/Plugins/OperatingSystem/Go/OperatingSystemGo.cpp

     TargetSP target_sp = m_process->CalculateTarget();
     if (!target_sp)
         return false;
-    m_allg_sp = FindGlobal(target_sp, "runtime.allg");
-    m_allglen_sp = FindGlobal(target_sp, "runtime.allglen");
+    // Go 1.6 stores goroutines in a slice called runtime.allgs
+    ValueObjectSP allgs_sp = FindGlobal(target_sp, "runtime.allgs");
+    if (allgs_sp)
+    {
+        m_allg_sp = allgs_sp->GetChildMemberWithName(ConstString("array"), true);
+        m_allglen_sp = allgs_sp->GetChildMemberWithName(ConstString("len"), true);
+    }
+    else
+    {
+        // Go 1.4 stores goroutines in the variable runtime.allg.
+        m_allg_sp = FindGlobal(target_sp, "runtime.allg");
+        m_allglen_sp = FindGlobal(target_sp, "runtime.allglen");
+    }
 
     if (m_allg_sp && !m_allglen_sp)
     {