[llvm-branch-commits] [llvm] [AArch64][PAC] Lower authenticated calls with ptrauth bundles. (PR #85736)

[Ahmed Bougacha via llvm-branch-commits]

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@@ -1694,6 +1718,35 @@ let Predicates = [HasPAuth] in {
     def BLRABZ  : AuthOneOperand<0b001, 1, "blrabz">;
   }
 
+  // BLRA pseudo, generalized version of BLRAA/BLRAB/Z.
+  // This directly manipulates x16/x17, which are the only registers the OS
+  // guarantees are safe to use for sensitive operations.
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ahmedbougacha wrote:

Unfortunately this sort of thing isn't documented.  We do describe the general contract in the security model sections of the clang docs.
For ELF it might make sense to have a formalization in the PAuth ABI, but that would have to be actually honored in an OS;  I imagine it currently isn't anywhere other than Darwin.

https://github.com/llvm/llvm-project/pull/85736