libcxx: Switch to use __gnu_unwind_frame() for libunwind.

[logan]

Summary

As a step to fix libunwind unw_step(), a new function
__gnu_unwind_frame() has been introduced to libunwind, and it is
required to use this function so that some libunwind internal data
structure can be updated properly.

Depends On: D9961

[rengolin]

And I imagine that this will also fix the problem we had earlier with undefined __gnu_unwind_frame, right?

If that's so, this one also looks good to me.

Thanks for the work!

--renato

[logan]

Hi Anton and Renato,

Thanks for reviewing. Committed as rL238561.

[logan]

In D9962#177558, @rengolin wrote:

And I imagine that this will also fix the problem we had earlier with undefined __gnu_unwind_frame, right?

I haven't encountered this problem by myself. But I believe this should fix your problem.

src/cxa_personality.cpp

if (actions & _UA_CLEANUP_PHASE)
         //     if we were called improperly).
         return results.reason;
     }
     // We were called improperly: neither a phase 1 or phase 2 search
     return _URC_FATAL_PHASE1_ERROR;
 }
 #else
 
-#if !LIBCXXABI_USE_LLVM_UNWINDER
-extern "C" _Unwind_Reason_Code __gnu_unwind_frame(_Unwind_Exception*, _Unwind_Context*);
-#endif
+extern "C" _Unwind_Reason_Code __gnu_unwind_frame(_Unwind_Exception*,
+                                                  _Unwind_Context*);
 
 // Helper function to unwind one frame.
 // ARM EHABI 7.3 and 7.4: If the personality function returns _URC_CONTINUE_UNWIND, the
 // personality routine should update the virtual register set (VRS) according to the
 // corresponding frame unwinding instructions (ARM EHABI 9.3.)
 static _Unwind_Reason_Code continue_unwind(_Unwind_Exception* unwind_exception,
                                            _Unwind_Context* context)
 {
-#if LIBCXXABI_USE_LLVM_UNWINDER
-    // ARM EHABI # 6.2, # 9.2
-    //
-    //  +---- ehtp
-    //  v
-    // +--------------------------------------+
-    // | +--------+--------+--------+-------+ |
-    // | |0| prel31 to __gxx_personality_v0 | |
-    // | +--------+--------+--------+-------+ |
-    // | |      N |      unwind opcodes     | |  <-- unwind_opcodes
-    // | +--------+--------+--------+-------+ |
-    // | | Word 2        unwind opcodes     | |
-    // | +--------+--------+--------+-------+ |
-    // | ...                                  |
-    // | +--------+--------+--------+-------+ |
-    // | | Word N        unwind opcodes     | |
-    // | +--------+--------+--------+-------+ |
-    // | | LSDA                             | |  <-- lsda
-    // | | ...                              | |
-    // | +--------+--------+--------+-------+ |
-    // +--------------------------------------+
-
-    uint32_t *unwind_opcodes = unwind_exception->pr_cache.ehtp + 1;
-    size_t opcode_words = ((*unwind_opcodes >> 24) & 0xff) + 1;
-    if (_Unwind_VRS_Interpret(context, unwind_opcodes, 1, opcode_words * 4) !=
-        _URC_CONTINUE_UNWIND)
-        return _URC_FAILURE;
-#else
     if (__gnu_unwind_frame(unwind_exception, context) != _URC_OK)
         return _URC_FAILURE;
-#endif
     return _URC_CONTINUE_UNWIND;
 }
 
 // ARM register names
 #if !LIBCXXABI_USE_LLVM_UNWINDER
 static const uint32_t REG_UCB = 12;  // Register to save _Unwind_Control_Block
 #endif
 static const uint32_t REG_SP = 13;