[llvm] [BOLT] Gadget scanner: reformulate the state for data-flow analysis (PR #131898)

[Kristof Beyls via llvm-commits]

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@@ -551,6 +551,16 @@ class MCPlusBuilder {
     return Analysis->isReturn(Inst);
   }
 
+  /// Returns the registers that are trusted at function entry.
+  ///
+  /// Each register should be treated as if a successfully authenticated
+  /// pointer was written to it before entering the function (i.e. the
+  /// pointer is safe to jump to as well as to be signed).
+  virtual SmallVector<MCPhysReg> getTrustedLiveInRegs() const {
+    llvm_unreachable("not implemented");
+    return {};
+  }
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kbeyls wrote:

I'm wondering if `MCPlusBuilder` is the right place for this to live...
The reason why I'm not sure is that to me it seems that `MCPlusBuilder` is mostly about querying the property of instructions, maybe at most relative to an assumed ABI.
It seems to me that `getTrustedLiveInRegs` might be encoding an assumed, implicit, threat model too?

Apologies for not explaining this very well. I'm just trying to make sure this function goes into the most appropriate place.

https://github.com/llvm/llvm-project/pull/131898