Fix _Unwind_Backtrace for libc++abi built with libgcc.

[logan]

Summary

Implement an undocumented _US_FORCE_UNWIND state for force
unwinding.

[rengolin]

src/cxa_personality.cpp

1107

Why do you need to clear the forced flag?

[jroelofs]

src/cxa_personality.cpp

1105

Why not add this to the public interface in include/unwind.h? If we're matching the behavior between gcc's unwinder, then perhaps it makes sense to 'advertise' that fact.

1112

can the state ever be set to just _US_FORCE_UNWIND? Also, continue_unwind() takes three parameters now... can you rebase this patch?

[jroelofs]

LGTM.

src/cxa_personality.cpp

1107

The _US_* things are a bitmask. Not clearing it means that the switch below won't match it.

1112

can the state ever be set to just _US_FORCE_UNWIND?

Nevermind about that part.

[jroelofs]

src/cxa_personality.cpp

1112

Also, nevermind about the rebase. I see that you've changed the signature of this function in a different patch in the series.

[danalbert]

src/cxa_personality.cpp

1106

It's already a uint32_t, what do you need the cast for? If you really do need a cast, use something explicitly sized.

1107

Would be more intention revealing to clear the flag for the switch condition itself.

[logan]

Address the review comments.

[logan]

src/cxa_personality.cpp

1105

Thanks. I have moved this flag to unwind.h.

1106

Thanks. Removed.

1107

Some explaination on this: Although _Unwind_Backtrace() only uses one of the case, it is required to implement the personality for both _US_VIRTUAL_UNWIND_FRAME and _US_UNWIND_FRAME_STARTING cases.

p.s. The later case is used by _Unwind_ForcedUnwind(). However, it is not working yet. I am debugging at the moment.

[logan]

Make Unwind-EHABI.h become C compatible.

[logan]

Recover the previous patch set.

This differential is incorrectly covered by incorrect patch set.

[logan]

Thanks. Committed as rL226820.

src/cxa_personality.cpp

 
 #if !LIBCXXABI_USE_LLVM_UNWINDER
     // Copy the address of _Unwind_Control_Block to r12 so that
     // _Unwind_GetLanguageSpecificData() and _Unwind_GetRegionStart() can
     // return correct address.
     _Unwind_SetGR(context, REG_UCB, reinterpret_cast<uint32_t>(unwind_exception));
 #endif
 
+    // Check the undocumented force unwinding behavior
+    const unsigned _US_FORCE_UNWIND = 8u;
+    bool is_force_unwinding = static_cast<unsigned>(state) & _US_FORCE_UNWIND;
+    state = static_cast<_Unwind_State>(static_cast<unsigned>(state) & ~_US_FORCE_UNWIND);
+
     scan_results results;
     switch (state) {
     case _US_VIRTUAL_UNWIND_FRAME:
+        if (is_force_unwinding)
+            return continue_unwind(unwind_exception, context);
+
         // Phase 1 search:  All we're looking for in phase 1 is a handler that halts unwinding
         scan_eh_tab(results, _UA_SEARCH_PHASE, native_exception, unwind_exception, context);
         if (results.reason == _URC_HANDLER_FOUND)
         {
             unwind_exception->barrier_cache.sp = _Unwind_GetGR(context, REG_SP);
             if (native_exception)
                 save_results_to_barrier_cache(unwind_exception, results);
             return _URC_HANDLER_FOUND;