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

[Aiden Grossman via llvm-commits]

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@@ -207,18 +216,35 @@ 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 for switching.
+      errno = 0;
+      unsigned long PacKeys = prctl_wrapper(PR_PAC_GET_ENABLED_KEYS);
+      if ((long)PacKeys < 0 || errno == EINVAL)
+        return nullptr;
+
       // Disable all PAC keys. Note that while we expect the measurements to
       // be the same with PAC keys disabled, they could potentially be lower
       // since authentication checks are bypassed.
-      if (prctl(PR_PAC_SET_ENABLED_KEYS,
-                PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY |
-                    PR_PAC_APDBKEY, // all keys
-                0,                  // disable all
-                0, 0) < 0) {
-        return "Failed to disable PAC keys";
+      if ((long)PacKeys != 0) {
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boomanaiden154 wrote:

Here too regarding casting.

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