[llvm] [BOLT][binary-analysis] Add initial pac-ret gadget scanner (PR #122304)

[Jacob Bramley via llvm-commits]

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@@ -0,0 +1,517 @@
+//===- bolt/Passes/NonPacProtectedRetAnalysis.cpp -------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a pass that looks for any AArch64 return instructions
+// that may not be protected by PAuth authentication instructions when needed.
+//
+// When needed = the register used to return (almost always X30), is potentially
+// written to between the AUThentication instruction and the RETurn instruction.
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jacobbramley wrote:

I think the intention is correct, but the wording is slightly confusing. Given that the behaviour is explained in detail below, I'd be tempted to remove this "when needed" sentence.

https://github.com/llvm/llvm-project/pull/122304