[llvm] [llvm-exegesis][AArch64] Check for PAC keys before disabling them (PR #138643)

[David Green via llvm-commits]

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@@ -207,15 +207,28 @@ class ExegesisAArch64Target : public ExegesisTarget {
 
     if (isPointerAuth(Opcode)) {
 #if defined(__aarch64__) && defined(__linux__)
+
+      // For some systems with existing PAC keys set, it is better to
+      // check the existing state of the key before setting it.
+      // For systems without PAC, this is a No-op but with PAC, it is
+      // safer to check the existing key state and then disable/enable them.
+      // Hence the guard placed for switching.
+      unsigned long PacKeys = 0;
+      if (prctl(PR_PAC_GET_ENABLED_KEYS, &pac_keys, 0, 0, 0) < 0) {
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davemgreen wrote:

pac_keys->PacKeys ;)

https://github.com/llvm/llvm-project/pull/138643