[aarch64][mc] Don't lookup symbols when there is no symbol lookup cal…

…lback

Summary: When run under llvm-mc-disassemble-fuzzer, there is no symbol lookup callback so tryAddingSymbolicOperand() must fail gracefully instead of crashing

Reviewers: aemerson, javed.absar

Reviewed By: aemerson

Subscribers: lhames, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D51005

llvm-svn: 340287

llvm/lib/Target/AArch64/Disassembler/AArch64ExternalSymbolizer.cpp

@@ -60,6 +60,8 @@ getVariant(uint64_t LLVMDisassembler_VariantKind) {
 bool AArch64ExternalSymbolizer::tryAddingSymbolicOperand(
     MCInst &MI, raw_ostream &CommentStream, int64_t Value, uint64_t Address,
     bool IsBranch, uint64_t Offset, uint64_t InstSize) {
+  if (!SymbolLookUp)
+    return false;
   // FIXME: This method shares a lot of code with
   //        MCExternalSymbolizer::tryAddingSymbolicOperand. It may be possible
   //        refactor the MCExternalSymbolizer interface to allow more of this