[compiler-rt] [libcxx] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (PR #143230)

[Oliver Hunt via llvm-commits]

================
@@ -557,7 +630,21 @@ set_registers(_Unwind_Exception* unwind_exception, _Unwind_Context* context,
                 reinterpret_cast<uintptr_t>(unwind_exception));
   _Unwind_SetGR(context, __builtin_eh_return_data_regno(1),
                 static_cast<uintptr_t>(results.ttypeIndex));
+#if __has_feature(ptrauth_qualifier)
+  auto stackPointer = _Unwind_GetGR(context, UNW_REG_SP);
----------------
ojhunt wrote:

Sigh, i've been fighting some local build issues and was wanting to get bot feedback while getting my local build working again (see https://github.com/llvm/llvm-project/pull/156607 that I ran into because I was accidentally building clang fat). I should have commented that this was not ready for re-review (though the feedback is needed, it would hopefully mitigate manually finding failures)

Including libunwind.h is necessary -- pointer auth makes these ABI linked, and while we _could_ redeclare these in cxxabi that would obscure the linkage _and_ mean changes are  not automatic and silently break.

https://github.com/llvm/llvm-project/pull/143230