[libunwind] [libunwind] Call `__arm_za_disable` before entering EH (PR #160905)

[Benjamin Maxwell via cfe-commits]

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@@ -1971,6 +1975,32 @@ Registers_arm64::operator=(const Registers_arm64 &other) {
   return *this;
 }
 
+void Registers_arm64::jumpto() {
+#if !defined(__APPLE__)
+  // The platform must ensure that all the following conditions are true on
+  // entry to EH:
+  //
+  // - PSTATE.SM is 0.
+  // - PSTATE.ZA is 0.
+  // - TPIDR2_EL0 is null.
+  //
+  // The first point is ensured by routines for throwing exceptions having a
+  // non-streaming interface. TPIDR2_EL0 is set to null and ZA disabled by
+  // calling __arm_za_disable.
+  //
+  // See:
+  // https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#exceptions
----------------
MacDue wrote:

I'm not sure what that'd be here? I'm aware GCC versions their symbols, but this symbol could be provided by libgcc/ibgcc_s or compiler-rt, and I'm not sure what version information is generally available. 

https://github.com/llvm/llvm-project/pull/160905