[libunwind][ARM] Handle end of stack during unwind

[danielkiss]

Summary

When unwind step reaches the end of the stack that means the force unwind should notify the stop function.
This is not an error, it could mean just the thread is cleaned up completely.

[danielkiss]

Rerun clang-format.

[danielkiss]

Make the CI happy.

[danielkiss]

Ping

[mstorsjo]

Looks reasonable I think. Is this a deficiency in the EHABI implementation only, i.e. this aspect works as it should in the regular dwarf implementation?

[danielkiss]

In D109856#3154763, @mstorsjo wrote:

Looks reasonable I think. Is this a deficiency in the EHABI implementation only, i.e. this aspect works as it should in the regular dwarf implementation?

Yes, it works on dwarf already ( also the test pass on X86/Aarch64 ).

[mstorsjo]

In D109856#3155235, @danielkiss wrote:

In D109856#3154763, @mstorsjo wrote:

Looks reasonable I think. Is this a deficiency in the EHABI implementation only, i.e. this aspect works as it should in the regular dwarf implementation?

Yes, it works on dwarf already ( also the test pass on X86/Aarch64 ).

Ok, thanks for the clarification!

libunwind/src/Unwind-EHABI.cpp

static _Unwind_Reason_Code unwindOneFrame(_Unwind_State state,
   // of the correct stack frame.
   _Unwind_Reason_Code result =
       ProcessDescriptors(state, ucbp, context, format, lsda,
                          ucbp->pr_cache.additional);
 
   if (result != _URC_CONTINUE_UNWIND)
     return result;
 
-  if (__unw_step(reinterpret_cast<unw_cursor_t *>(context)) != UNW_STEP_SUCCESS)
-    return _URC_FAILURE;
+  switch (__unw_step(reinterpret_cast<unw_cursor_t *>(context))) {
+  case UNW_STEP_SUCCESS:
     return _URC_CONTINUE_UNWIND;
+  case UNW_STEP_END:
+    return _URC_END_OF_STACK;
+  default:
+    return _URC_FAILURE;
+  }
 }
 
 // Generates mask discriminator for _Unwind_VRS_Pop, e.g. for _UVRSC_CORE /
 // _UVRSD_UINT32.
 uint32_t RegisterMask(uint8_t start, uint8_t count_minus_one) {
   return ((1U << (count_minus_one + 1)) - 1) << start;
 }
 
#endif
   // said it would...
   return _URC_FATAL_PHASE2_ERROR;
 }
 
 static _Unwind_Reason_Code
 unwind_phase2_forced(unw_context_t *uc, unw_cursor_t *cursor,
                      _Unwind_Exception *exception_object, _Unwind_Stop_Fn stop,
                      void *stop_parameter) {
+  bool endOfStack = false;
   // See comment at the start of unwind_phase1 regarding VRS integrity.
   __unw_init_local(cursor, uc);
   _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_force(ex_ojb=%p)",
                              static_cast<void *>(exception_object));
   // Walk each frame until we reach where search phase said to stop
-  while (true) {
+  while (!endOfStack) {
     // Update info about this frame.
     unw_proc_info_t frameInfo;
     if (__unw_get_proc_info(cursor, &frameInfo) != UNW_ESUCCESS) {
       _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): __unw_step "
                                  "failed => _URC_END_OF_STACK",
                                  (void *)exception_object);
       return _URC_FATAL_PHASE2_ERROR;
     }
if (frameInfo.handler != 0) {
       case _URC_INSTALL_CONTEXT:
         _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
                                    "personality returned "
                                    "_URC_INSTALL_CONTEXT",
                                    (void *)exception_object);
         // We may get control back if landing pad calls _Unwind_Resume().
         __unw_resume(cursor);
         break;
+      case _URC_END_OF_STACK:
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned "
+                                   "_URC_END_OF_STACK",
+                                   (void *)exception_object);
+        // Personalty routine did the step and it can't step forward.
+        endOfStack = true;
+        break;
       default:
         // Personality routine returned an unknown result code.
         _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
                                    "personality returned %d, "
                                    "_URC_FATAL_PHASE2_ERROR",
                                    (void *)exception_object, personalityResult);
         return _URC_FATAL_PHASE2_ERROR;
       }