+2018-10-19  Tamar Christina  <tamar.christina@arm.com>
+
+       * testsuite/gas/arm/undefined-insn-arm.d: New test.
+       * testsuite/gas/arm/undefined-insn-thumb.d: New test.
+       * testsuite/gas/arm/undefined-insn.s: New test.
+
 2018-10-19  Fredrik Noring  <noring@nocrew.org>
 
        * testsuite/gas/mips/r5900.s: Extend the R5900 short loop fix
 
--- /dev/null
+#name: Undefined binary printing in arm mode
+#skip: *-unknown-pe *-*-vxworks
+#source: undefined-insn.s
+#objdump: -D -b binary -m armv7e-m
+#...
 
--- /dev/null
+#name: Undefined binary printing in thumb mode
+#skip: *-unknown-pe *-*-vxworks
+#source: undefined-insn.s
+#objdump: -D -b binary -m armv7e-m -M force-thumb
+#...
 
--- /dev/null
+       .inst 0xffffffff
 
+2018-10-19  Tamar Christina  <tamar.christina@arm.com>
+
+       * arm-dis.c (UNKNOWN_INSTRUCTION_32BIT): Format specifier for arm mode.
+       (UNKNOWN_INSTRUCTION_16BIT): Format specifier for thumb mode.
+       (print_insn_arm, print_insn_thumb16, print_insn_thumb32): Use them.
+
 2018-10-16  Matthew Malcomson  <matthew.malcomson@arm.com>
 
        * aarch64-opc.c (struct operand_qualifier_data): Change qualifier data
 
 } opcode_sentinels;
 
 #define UNDEFINED_INSTRUCTION      "\t\t; <UNDEFINED> instruction: %0-31x"
+#define UNKNOWN_INSTRUCTION_32BIT  "\t\t; <UNDEFINED> instruction: %08x"
+#define UNKNOWN_INSTRUCTION_16BIT  "\t\t; <UNDEFINED> instruction: %04x"
 #define UNPREDICTABLE_INSTRUCTION  "\t; <UNPREDICTABLE>"
 
 /* Common coprocessor opcodes shared between Arm and Thumb-2.  */
          return;
        }
     }
-  abort ();
+  func (stream, UNKNOWN_INSTRUCTION_32BIT, (unsigned)given);
+  return;
 }
 
 /* Print one 16-bit Thumb instruction from PC on INFO->STREAM.  */
       }
 
   /* No match.  */
-  abort ();
+  func (stream, UNKNOWN_INSTRUCTION_16BIT, (unsigned)given);
+  return;
 }
 
 /* Return the name of an V7M special register.  */
       }
 
   /* No match.  */
-  abort ();
+  func (stream, UNKNOWN_INSTRUCTION_32BIT, (unsigned)given);
+  return;
 }
 
 /* Print data bytes on INFO->STREAM.  */