Address review comments

Author: atrosinenko

bolt/include/bolt/Core/MCPlusBuilder.h

@@ -610,7 +610,8 @@ class MCPlusBuilder {
   getRegUsedAsIndirectBranchDest(const MCInst &Inst,
                                  bool &IsAuthenticatedInternally) const {
     llvm_unreachable("not implemented");
-    return 0;
+    return 0; // Unreachable. A valid register should be returned by the
+              // target implementation.
   }
 
   /// Returns the register containing an address safely materialized by `Inst`

bolt/lib/Passes/PAuthGadgetScanner.cpp

@@ -753,7 +753,6 @@ shouldReportReturnGadget(const BinaryContext &BC, const MCInstReference &Inst,
   if (IsAuthenticated)
     return std::nullopt;
 
-  assert(*RetReg != BC.MIB->getNoRegister());
   LLVM_DEBUG({
     traceInst(BC, "Found RET inst", Inst);
     traceReg(BC, "RetReg", *RetReg);
@@ -779,7 +778,7 @@ shouldReportCallGadget(const BinaryContext &BC, const MCInstReference &Inst,
   if (IsAuthenticated)
     return std::nullopt;
 
-  assert(DestReg != BC.MIB->getNoRegister());
+  assert(DestReg != BC.MIB->getNoRegister() && "Valid register expected");
   LLVM_DEBUG({
     traceInst(BC, "Found call inst", Inst);
     traceReg(BC, "Call destination reg", DestReg);
@@ -800,7 +799,6 @@ shouldReportSigningOracle(const BinaryContext &BC, const MCInstReference &Inst,
   if (!SignedReg)
     return std::nullopt;
 
-  assert(*SignedReg != BC.MIB->getNoRegister());
   LLVM_DEBUG({
     traceInst(BC, "Found sign inst", Inst);
     traceReg(BC, "Signed reg", *SignedReg);

bolt/test/binary-analysis/AArch64/gs-pauth-signing-oracles.s

@@ -1000,11 +1000,37 @@ inst_ldraa_wb:
         .type   inst_ldrab_wb,@function
 inst_ldrab_wb:
 // CHECK-NOT: inst_ldrab_wb
-        ldraa   x2, [x0]!
+        ldrab   x2, [x0]!
         pacda   x0, x1
         ret
         .size inst_ldrab_wb, .-inst_ldrab_wb
 
+// Non write-back forms of LDRA(A|B) instructions do not modify the address
+// register, and thus do not make it safe.
+
+        .globl  inst_ldraa_non_wb
+        .type   inst_ldraa_non_wb,@function
+inst_ldraa_non_wb:
+// CHECK-LABEL: GS-PAUTH: signing oracle found in function inst_ldraa_non_wb, basic block {{[^,]+}}, at address
+// CHECK-NEXT:  The instruction is     {{[0-9a-f]+}}:      pacdb   x0, x1
+// CHECK-NEXT:  The 0 instructions that write to the affected registers after any authentication are:
+        ldraa   x2, [x0]
+        pacdb   x0, x1
+        ret
+        .size inst_ldraa_non_wb, .-inst_ldraa_non_wb
+
+        .globl  inst_ldrab_non_wb
+        .type   inst_ldrab_non_wb,@function
+inst_ldrab_non_wb:
+// CHECK-LABEL: GS-PAUTH: signing oracle found in function inst_ldrab_non_wb, basic block {{[^,]+}}, at address
+// CHECK-NEXT:  The instruction is     {{[0-9a-f]+}}:      pacda   x0, x1
+// CHECK-NEXT:  The 0 instructions that write to the affected registers after any authentication are:
+        autia   x0, x3
+        ldrab   x2, [x0]
+        pacda   x0, x1
+        ret
+        .size inst_ldrab_non_wb, .-inst_ldrab_non_wb
+
         .globl  main
         .type   main,@function
 main: