The Oracle Studio Performance Analyzer walks x86 instructions while a target
application is running as part of call-stack unwind in order to attribute
performance metrics to user source code. Starting with Java 9, there have
been problematic instruction byte sequences that have caused SEGVs. They
look like:
    jmp *(%reg)
    nop
where the nop can take many different forms and apparently serves to pad out
until the next multiple-of-8 boundary. It is desirable that the end of a
code block, when there will be no more executable instructions, would be
indicated with an x86 ud2 (0x0f 0x0b) before the nop so that there is a clear
indicator that no further bytes should be walked. Please let me know if
there is anything about this request that needs further explanation.