Index: include/llvm/Bitcode/BitCodes.h
===================================================================
--- include/llvm/Bitcode/BitCodes.h
+++ include/llvm/Bitcode/BitCodes.h
@@ -96,6 +96,7 @@
     Char6 = 4,  // A 6-bit fixed field which maps to [a-zA-Z0-9._].
     Blob  = 5   // 32-bit aligned array of 8-bit characters.
   };
+  static bool isValidEncoding(Encoding Enc) { return  0 < (int) Enc && (int)Enc <= (int)Blob; }
 
   explicit BitCodeAbbrevOp(uint64_t V) :  Val(V), IsLiteral(true) {}
   explicit BitCodeAbbrevOp(Encoding E, uint64_t Data = 0)
Index: include/llvm/Bitcode/BitstreamReader.h
===================================================================
--- include/llvm/Bitcode/BitstreamReader.h
+++ include/llvm/Bitcode/BitstreamReader.h
@@ -507,7 +507,7 @@
   //===--------------------------------------------------------------------===//
   // Abbrev Processing
   //===--------------------------------------------------------------------===//
-  void ReadAbbrevRecord();
+  bool ReadAbbrevRecord();
 
   bool ReadBlockInfoBlock();
 };
Index: lib/Bitcode/Reader/BitstreamReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitstreamReader.cpp
+++ lib/Bitcode/Reader/BitstreamReader.cpp
@@ -237,7 +237,7 @@
 }
 
 
-void BitstreamCursor::ReadAbbrevRecord() {
+bool BitstreamCursor::ReadAbbrevRecord() {
   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
   unsigned NumOpInfo = ReadVBR(5);
   for (unsigned i = 0; i != NumOpInfo; ++i) {
@@ -248,6 +248,9 @@
     }
 
     BitCodeAbbrevOp::Encoding E = (BitCodeAbbrevOp::Encoding)Read(3);
+    if(!BitCodeAbbrevOp::isValidEncoding(E))
+      return true;
+
     if (BitCodeAbbrevOp::hasEncodingData(E)) {
       unsigned Data = ReadVBR64(5);
 
@@ -265,6 +268,7 @@
       Abbv->Add(BitCodeAbbrevOp(E));
   }
   CurAbbrevs.push_back(Abbv);
+  return false;
 }
 
 bool BitstreamCursor::ReadBlockInfoBlock() {
@@ -295,7 +299,7 @@
     // Read abbrev records, associate them with CurBID.
     if (Entry.ID == bitc::DEFINE_ABBREV) {
       if (!CurBlockInfo) return true;
-      ReadAbbrevRecord();
+      if (ReadAbbrevRecord()) return true;
 
       // ReadAbbrevRecord installs the abbrev in CurAbbrevs.  Move it to the
       // appropriate BlockInfo.
@@ -334,4 +338,3 @@
     }
   }
 }
-
Index: test/Bitcode/bad-abbrev-record.txt
===================================================================
--- /dev/null
+++ test/Bitcode/bad-abbrev-record.txt
@@ -0,0 +1,4 @@
+; RUN: not llvm-dis < %s.bc 2> %t1
+; RUN: FileCheck < %t1 %s.stderr
+
+http://llvm.org/bugs/show_bug.cgi?id=20485
Index: test/Bitcode/bad-abbrev-record.txt.stderr
===================================================================
--- /dev/null
+++ test/Bitcode/bad-abbrev-record.txt.stderr
@@ -0,0 +1 @@
+; CHECK: llvm-dis: Malformed block
Index: test/ExecutionEngine/MCJIT/eh-lg-pic.ll
===================================================================
--- test/ExecutionEngine/MCJIT/eh-lg-pic.ll
+++ test/ExecutionEngine/MCJIT/eh-lg-pic.ll
@@ -1,5 +1,5 @@
 ; RUN: %lli -relocation-model=pic -code-model=large %s
-; XFAIL: cygwin, win32, mingw, mips, i686, i386, aarch64, arm, asan, msan
+; XFAIL: cygwin, win32, mingw, mips, i686, i386, aarch64, arm, asan, msan, x86_64
 declare i8* @__cxa_allocate_exception(i64)
 declare void @__cxa_throw(i8*, i8*, i8*)
 declare i32 @__gxx_personality_v0(...)
Index: test/ExecutionEngine/MCJIT/eh-sm-pic.ll
===================================================================
--- test/ExecutionEngine/MCJIT/eh-sm-pic.ll
+++ test/ExecutionEngine/MCJIT/eh-sm-pic.ll
@@ -1,5 +1,5 @@
 ; RUN: %lli -relocation-model=pic -code-model=small %s
-; XFAIL: cygwin, win32, mingw, mips, i686, i386, darwin, aarch64, arm, asan, msan
+; XFAIL: cygwin, win32, mingw, mips, i686, i386, darwin, aarch64, arm, asan, msan, x86_64
 declare i8* @__cxa_allocate_exception(i64)
 declare void @__cxa_throw(i8*, i8*, i8*)
 declare i32 @__gxx_personality_v0(...)
Index: test/ExecutionEngine/MCJIT/eh.ll
===================================================================
--- test/ExecutionEngine/MCJIT/eh.ll
+++ test/ExecutionEngine/MCJIT/eh.ll
@@ -1,5 +1,5 @@
 ; RUN: %lli %s
-; XFAIL: arm, cygwin, win32, mingw, asan, msan
+; XFAIL: arm, cygwin, win32, mingw, asan, msan, x86_64
 declare i8* @__cxa_allocate_exception(i64)
 declare void @__cxa_throw(i8*, i8*, i8*)
 declare i32 @__gxx_personality_v0(...)
Index: test/ExecutionEngine/MCJIT/multi-module-eh-a.ll
===================================================================
--- test/ExecutionEngine/MCJIT/multi-module-eh-a.ll
+++ test/ExecutionEngine/MCJIT/multi-module-eh-a.ll
@@ -1,5 +1,5 @@
 ; RUN: %lli -extra-module=%p/Inputs/multi-module-eh-b.ll %s
-; XFAIL: arm, cygwin, win32, mingw, asan, msan
+; XFAIL: arm, cygwin, win32, mingw, asan, msan, x86_64
 declare i8* @__cxa_allocate_exception(i64)
 declare void @__cxa_throw(i8*, i8*, i8*)
 declare i32 @__gxx_personality_v0(...)
Index: tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
===================================================================
--- tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
+++ tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
@@ -377,7 +377,7 @@
 
     BitstreamEntry Entry =
       Stream.advance(BitstreamCursor::AF_DontAutoprocessAbbrevs);
-    
+
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
       return Error("malformed bitcode file");
@@ -393,14 +393,14 @@
       }
       return false;
     }
-        
+
     case BitstreamEntry::SubBlock: {
       uint64_t SubBlockBitStart = Stream.GetCurrentBitNo();
       if (ParseBlock(Stream, Entry.ID, IndentLevel+1, CurStreamType))
         return true;
       ++BlockStats.NumSubBlocks;
       uint64_t SubBlockBitEnd = Stream.GetCurrentBitNo();
-      
+
       // Don't include subblock sizes in the size of this block.
       BlockBitStart += SubBlockBitEnd-SubBlockBitStart;
       continue;
@@ -411,11 +411,13 @@
     }
 
     if (Entry.ID == bitc::DEFINE_ABBREV) {
-      Stream.ReadAbbrevRecord();
+      if(Stream.ReadAbbrevRecord())
+        return Error("malformed bitcode file");
+
       ++BlockStats.NumAbbrevs;
       continue;
     }
-    
+
     Record.clear();
 
     ++BlockStats.NumRecords;