Valgrind crashes with the following report: vex x86->IR: unhandled instruction bytes: 0xFF 0x69 0x38 0x90 ==24487== valgrind: Unrecognised instruction at address 0x8059713. ==24487== Your program just tried to execute an instruction that Valgrind ... The code looks like this: 080596f8 <NaClSwitch>: 80596f8: 58 pop %eax 80596f9: 31 c9 xor %ecx,%ecx 80596fb: 59 pop %ecx 80596fc: 8b 51 30 mov 0x30(%ecx),%edx 80596ff: 8b 69 14 mov 0x14(%ecx),%ebp 8059702: 8b 79 08 mov 0x8(%ecx),%edi 8059705: 8b 71 04 mov 0x4(%ecx),%esi 8059708: 8b 19 mov (%ecx),%ebx 805970a: 8e 69 2e mov 0x2e(%ecx),%gs 805970d: 8e 61 2c mov 0x2c(%ecx),%fs 8059710: 8e 41 2a mov 0x2a(%ecx),%es 8059713: ff 69 38 ljmp *0x38(%ecx) <<<<<<<<<<<<<<<<<<<<<< 8059716: 90 nop 8059717: 90 nop