[BOLT] Gadget scanner: do not crash on debug-printing CFI instructions

Some instruction-printing code used under LLVM_DEBUG does not handle CFI instructions well. While CFI instructions seem to be harmless for the correctness of the analysis results, they do not convey any useful information to the analysis either, so skip them early.

Author: atrosinenko

bolt/lib/Passes/PAuthGadgetScanner.cpp

@@ -429,6 +429,9 @@ class SrcSafetyAnalysis {
  }
 
  SrcState computeNext(const MCInst &Point, const SrcState &Cur) {
+ if (BC.MIB->isCFI(Point))
+ return Cur;
+
  SrcStatePrinter P(BC);
  LLVM_DEBUG({
  dbgs() << " SrcSafetyAnalysis::ComputeNext(";
@@ -703,6 +706,8 @@ class CFGUnawareSrcSafetyAnalysis : public SrcSafetyAnalysis,
  SrcState S = createEntryState();
  for (auto &I : BF.instrs()) {
  MCInst &Inst = I.second;
+ if (BC.MIB->isCFI(Inst))
+ continue;
 
  // If there is a label before this instruction, it is possible that it
  // can be jumped-to, thus conservatively resetting S. As an exception,
@@ -982,6 +987,9 @@ class DstSafetyAnalysis {
  }
 
  DstState computeNext(const MCInst &Point, const DstState &Cur) {
+ if (BC.MIB->isCFI(Point))
+ return Cur;
+
  DstStatePrinter P(BC);
  LLVM_DEBUG({
  dbgs() << " DstSafetyAnalysis::ComputeNext(";
@@ -1151,6 +1159,8 @@ class CFGUnawareDstSafetyAnalysis : public DstSafetyAnalysis,
  DstState S = createUnsafeState();
  for (auto &I : llvm::reverse(BF.instrs())) {
  MCInst &Inst = I.second;
+ if (BC.MIB->isCFI(Inst))
+ continue;
 
  // If Inst can change the control flow, we cannot be sure that the next
  // instruction (to be executed in analyzed program) is the one processed
@@ -1341,6 +1351,9 @@ void FunctionAnalysisContext::findUnsafeUses(
  });
 
  iterateOverInstrs(BF, [&](MCInstReference Inst) {
+ if (BC.MIB->isCFI(Inst))
+ return;
+
  const SrcState &S = Analysis->getStateBefore(Inst);
 
  // If non-empty state was never propagated from the entry basic block
@@ -1404,6 +1417,9 @@ void FunctionAnalysisContext::findUnsafeDefs(
  });
 
  iterateOverInstrs(BF, [&](MCInstReference Inst) {
+ if (BC.MIB->isCFI(Inst))
+ return;
+
  const DstState &S = Analysis->getStateAfter(Inst);
 
  if (auto Report = shouldReportAuthOracle(BC, Inst, S))

bolt/test/binary-analysis/AArch64/gs-pauth-debug-output.s

@@ -329,6 +329,38 @@ auth_oracle:
 // PAUTH-EMPTY:
 // PAUTH-NEXT: Attaching leakage info to: 00000000: autia x0, x1 # DataflowDstSafetyAnalysis: dst-state<CannotEscapeUnchecked: BitVector, Insts: [0](0x{{[0-9a-f]+}} )>
 
+// Gadget scanner should not crash on CFI instructions, including when debug-printing them.
+// Note that the particular debug output is not checked, but BOLT should be
+// compiled with assertions enabled to support -debug-only argument.
+
+ .globl cfi_inst_df
+ .type cfi_inst_df,@function
+cfi_inst_df:
+ .cfi_startproc
+ sub sp, sp, #16
+ .cfi_def_cfa_offset 16
+ add sp, sp, #16
+ .cfi_def_cfa_offset 0
+ ret
+ .size cfi_inst_df, .-cfi_inst_df
+ .cfi_endproc
+
+ .globl cfi_inst_nocfg
+ .type cfi_inst_nocfg,@function
+cfi_inst_nocfg:
+ .cfi_startproc
+ sub sp, sp, #16
+ .cfi_def_cfa_offset 16
+
+ adr x0, 1f
+ br x0
+1:
+ add sp, sp, #16
+ .cfi_def_cfa_offset 0
+ ret
+ .size cfi_inst_nocfg, .-cfi_inst_nocfg
+ .cfi_endproc
+
 // CHECK-LABEL:Analyzing function main, AllocatorId = 1
  .globl main
  .type main,@function