Detect end-of-unwind

According to LibUnwind:src/x86_64/Gstep.c:85
(HEAD=c91974f30feac05055621e33ca101a371236c786), the x86_64 ABI states
that the end of the call stack is determined by either a null RBP or an
undefined return-address column in the DWARF.

include/dwarfinterpret/DwarfInterpret.hpp

@@ -81,6 +81,8 @@ class DwarfInterpret {
         /// Thrown when a Dwarf element is not found for a given PC
         class OF_WHAT_EXCEPTION(NotFound);
 
+        /// Thrown when trying to unwind a context with nothing more to unwind
+        class FirstUnwindFrame: public std::exception {};
 
         /// A Dwarf register
         typedef dwarf::core::FrameSection::register_def DwarfRegister;
@@ -172,7 +174,10 @@ class DwarfInterpret {
          */
         static UnwindContext get_current_unwind_context();
 
-        /// Unwinds once the given context
+        /** Unwinds once the given context
+         *
+         * \throws FirstUnwindFrame when trying to unwind the first frame.
+         */
         UnwindContext unwind_context(const UnwindContext& ctx);
 
     private:

src/DwarfInterpret.cpp

@@ -220,15 +220,24 @@ DwarfInterpret::UnwindContext DwarfInterpret::unwind_context(
          << cie.get_return_address_register_rule()
          << " at current IP = "
          << hex << ctx.rip << endl;
-    new_context.rip = interpret_dw_register(
-            cur_row,
-            cie.get_return_address_register_rule(),
-            ctx);
+    try {
+        new_context.rip = interpret_dw_register(
+                cur_row,
+                cie.get_return_address_register_rule(),
+                ctx);
+    } catch(const std::out_of_range& e) {
+        // An undefined RA means we've reached the end of the call stack
+        throw FirstUnwindFrame();
+    }
     cerr << "Yielding " << hex << new_context.rip << dec << endl;
     new_context.rbp = interpret_dw_register(
             cur_row,
             lib::DWARF_X86_64_RBP,
             ctx);
+    if(new_context.rbp == 0) {
+        // A null rbp means we've reached the end of the call stack
+        throw FirstUnwindFrame();
+    }
 
     new_context.rsp = interpret_dw_register(
             cur_row,

test/dump_my_threads.cpp

@@ -30,9 +30,9 @@ void dump_my_stack(int thread_id) {
                 cur_map_entry.pathname.c_str());
         fflush(stdout);
         try {
-        unw_context = dw.unwind_context(unw_context);
-        } catch(...) {
-            // Assume we're reached _start
+            unw_context = dw.unwind_context(unw_context);
+        } catch(const DwarfInterpret::FirstUnwindFrame& e) {
+            // We're reached the end of the stack
             return;
         }
     }