Revert libunwind change to fix backtrace segfault on aarch64

Revert commit 22b615a96593 from llvm git (by Daniel Kiss):

  [libunwind] Support for leaf function unwinding.

  Unwinding leaf function is useful in cases when the backtrace finds a
  leaf function for example when it caused a signal.
  This patch also add the support for the DW_CFA_undefined because it marks
  the end of the frames.

  Ryan Prichard provided code for the tests.

  Reviewed By: #libunwind, mstorsjo

  Differential Revision: https://reviews.llvm.org/D83573

  Reland with limit the test to the x86_64-linux target.

Bisection has shown that this particular upstream commit causes programs
using backtrace(3) on aarch64 to segfault. This affects the lang/rust
port, for instance. Until we can upstream to fix this problem, revert
the commit for now.

Reported by:	mikael
PR:		256864

2 files changed, 2 insertions, 10 deletions

diff --git a/contrib/llvm-project/libunwind/src/DwarfInstructions.hpp b/contrib/llvm-project/libunwind/src/DwarfInstructions.hpp
index c39cabe1f783..ee98f538d437 100644
--- a/contrib/llvm-project/libunwind/src/DwarfInstructions.hpp
+++ b/contrib/llvm-project/libunwind/src/DwarfInstructions.hpp
@@ -93,8 +93,7 @@ typename A::pint_t DwarfInstructions<A, R>::getSavedRegister(
 
   case CFI_Parser<A>::kRegisterInRegister:
     return registers.getRegister((int)savedReg.value);
-  case CFI_Parser<A>::kRegisterUndefined:
-    return 0;
+
   case CFI_Parser<A>::kRegisterUnused:
   case CFI_Parser<A>::kRegisterOffsetFromCFA:
     // FIX ME
@@ -118,7 +117,6 @@ double DwarfInstructions<A, R>::getSavedFloatRegister(
 
   case CFI_Parser<A>::kRegisterIsExpression:
   case CFI_Parser<A>::kRegisterUnused:
-  case CFI_Parser<A>::kRegisterUndefined:
   case CFI_Parser<A>::kRegisterOffsetFromCFA:
   case CFI_Parser<A>::kRegisterInRegister:
     // FIX ME
@@ -142,7 +140,6 @@ v128 DwarfInstructions<A, R>::getSavedVectorRegister(
 
   case CFI_Parser<A>::kRegisterIsExpression:
   case CFI_Parser<A>::kRegisterUnused:
-  case CFI_Parser<A>::kRegisterUndefined:
   case CFI_Parser<A>::kRegisterOffsetFromCFA:
   case CFI_Parser<A>::kRegisterInRegister:
     // FIX ME
@@ -193,10 +190,6 @@ int DwarfInstructions<A, R>::stepWithDwarf(A &addressSpace, pint_t pc,
                                     prolog.savedRegisters[i]));
           else
             return UNW_EBADREG;
-        } else if (i == (int)cieInfo.returnAddressRegister) {
-            // Leaf function keeps the return address in register and there is no
-            // explicit intructions how to restore it.
-            returnAddress = registers.getRegister(cieInfo.returnAddressRegister);
         }
       }
 
diff --git a/contrib/llvm-project/libunwind/src/DwarfParser.hpp b/contrib/llvm-project/libunwind/src/DwarfParser.hpp
index de0eb6de9d70..b41cc7bcfda2 100644
--- a/contrib/llvm-project/libunwind/src/DwarfParser.hpp
+++ b/contrib/llvm-project/libunwind/src/DwarfParser.hpp
@@ -69,7 +69,6 @@ public:
   };
   enum RegisterSavedWhere {
     kRegisterUnused,
-    kRegisterUndefined,
     kRegisterInCFA,
     kRegisterOffsetFromCFA,
     kRegisterInRegister,
@@ -503,7 +502,7 @@ bool CFI_Parser<A>::parseFDEInstructions(A &addressSpace,
               "malformed DW_CFA_undefined DWARF unwind, reg too big");
           return false;
         }
-        results->setRegisterLocation(reg, kRegisterUndefined, initialState);
+        results->setRegisterLocation(reg, kRegisterUnused, initialState);
         _LIBUNWIND_TRACE_DWARF("DW_CFA_undefined(reg=%" PRIu64 ")\n", reg);
         break;
       case DW_CFA_same_value: