Fixed an assert() exposed by fuzzing. Now, instead of assert when an invalid

instruction encoding is encountered, we just return a NULL ARMBasicMCBuilder
instance and the client just returns false to indicate disassembly error.

llvm-svn: 101201

2 files changed, 15 insertions, 10 deletions

diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
index 98bb6716c7f..aedd22eb3e8 100644
--- a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
+++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
@@ -3257,6 +3257,9 @@ ARMBasicMCBuilder::ARMBasicMCBuilder(unsigned opc, ARMFormat format,
 /// are responsible for freeing up of the allocated memory.  Cacheing can be
 /// performed by the API clients to improve performance.
 ARMBasicMCBuilder *llvm::CreateMCBuilder(unsigned Opcode, ARMFormat Format) {
+  // For "Unknown format", fail by returning a NULL pointer.
+  if ((unsigned)Format >= (array_lengthof(FuncPtrs) - 1))
+    return 0;
 
   return new ARMBasicMCBuilder(Opcode, Format,
                                ARMInsts[Opcode].getNumOperands());
diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.h b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.h
index 30752303708..f6cba5268dd 100644
--- a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.h
+++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.h
@@ -171,24 +171,33 @@ typedef ARMBasicMCBuilder *BO;
 typedef bool (*DisassembleFP)(MCInst &MI, unsigned Opcode, uint32_t insn,
     unsigned short NumOps, unsigned &NumOpsAdded, BO Builder);
 
+/// CreateMCBuilder - Return an ARMBasicMCBuilder that can build up the MC
+/// infrastructure of an MCInst given the Opcode and Format of the instr.
+/// Return NULL if it fails to create/return a proper builder.  API clients
+/// are responsible for freeing up of the allocated memory.  Cacheing can be
+/// performed by the API clients to improve performance.
+extern ARMBasicMCBuilder *CreateMCBuilder(unsigned Opcode, ARMFormat Format);
+
 /// ARMBasicMCBuilder - ARMBasicMCBuilder represents an ARM MCInst builder that
 /// knows how to build up the MCOperand list.
 class ARMBasicMCBuilder {
+  friend ARMBasicMCBuilder *CreateMCBuilder(unsigned Opcode, ARMFormat Format);
   unsigned Opcode;
   ARMFormat Format;
   unsigned short NumOps;
   DisassembleFP Disasm;
   Session *SP;
 
+private:
+  /// Opcode, Format, and NumOperands make up an ARM Basic MCBuilder.
+  ARMBasicMCBuilder(unsigned opc, ARMFormat format, unsigned short num);
+
 public:
   ARMBasicMCBuilder(ARMBasicMCBuilder &B)
     : Opcode(B.Opcode), Format(B.Format), NumOps(B.NumOps), Disasm(B.Disasm),
       SP(B.SP)
   {}
 
-  /// Opcode, Format, and NumOperands make up an ARM Basic MCBuilder.
-  ARMBasicMCBuilder(unsigned opc, ARMFormat format, unsigned short num);
-
   virtual ~ARMBasicMCBuilder() {}
 
   void setSession(Session *sp) {
@@ -236,13 +245,6 @@ private:
   }
 };
 
-/// CreateMCBuilder - Return an ARMBasicMCBuilder that can build up the MC
-/// infrastructure of an MCInst given the Opcode and Format of the instr.
-/// Return NULL if it fails to create/return a proper builder.  API clients
-/// are responsible for freeing up of the allocated memory.  Cacheing can be
-/// performed by the API clients to improve performance.
-extern ARMBasicMCBuilder *CreateMCBuilder(unsigned Opcode, ARMFormat Format);
-
 } // namespace llvm
 
 #endif