Maximum Zeal ~ Emphatic prose on indulged fascinations

How to print assembly for your Java code in OS X

0. Write program.

package name.dhruba;
public class Main {
  public static void main(String[] args) {
    System.out.println("Hello World!");

1. Add JVM arguments to your program.

-XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly

2. Run your program. You will probably see the output below.

Java HotSpot(TM) 64-Bit Server VM warning: PrintAssembly is enabled; turning on DebugNonSafepoints to gain additional output
Could not load hsdis-amd64.dylib; library not loadable; PrintAssembly is disabled
Hello World!
Process finished with exit code 0

3. Download the missing library from here. The direct link to the lib file itself is here. I downloaded the one named ‘gnu-bsd-libhsdis-amd64.dylib’ as I’m running 64-bit. This produces a file on your system called ‘hsdis-amd64.dylib’.

4. Move it to where, the JDK that you are running with, looks for it. I was using Java8.

sudo mv ~/Downloads/hsdis-amd64.dylib /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/hsdis-amd64.dylib

5. Run your program again and see assembly! The output for Hello World is huge so I can’t paste all of it here but here’s the initial bit where you can see that the disassembler has been loaded.

Java HotSpot(TM) 64-Bit Server VM warning: PrintAssembly is enabled; turning on DebugNonSafepoints to gain additional output
Loaded disassembler from /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/hsdis-amd64.dylib
Decoding compiled method 0x000000010f4c23d0:
[Disassembling for mach='i386:x86-64']
[Entry Point]
  # {method} {0x00000001280fe660} 'arraycopy' '(Ljava/lang/Object;ILjava/lang/Object;II)V' in 'java/lang/System'
  # parm0:    rsi:rsi   = 'java/lang/Object'
  # parm1:    rdx       = int
  # parm2:    rcx:rcx   = 'java/lang/Object'
  # parm3:    r8        = int
  # parm4:    r9        = int
  #           [sp+0x60]  (sp of caller)
  0x000000010f4c2540: mov    0x8(%rsi),%r10d
  0x000000010f4c2544: shl    $0x3,%r10
  0x000000010f4c2548: cmp    %r10,%rax
  0x000000010f4c254b: je     0x000000010f4c2558
  0x000000010f4c2551: jmpq   0x000000010f407b60  ;   {runtime_call}
  0x000000010f4c2556: xchg   %ax,%ax

Credit: Nitsan Wakart.

Upcoming Coursera course: Principles of Reactive Programming

Just a quick note to say that a new Coursera course begins on 4th Nov 2013 that looks very interesting indeed titled ‘Principles of Reactive Programming‘ taught by Martin Odersky, Erik Meijer and Roland Kuhn. It is intended as a follow on course from its precursor course ‘Functional Programming Principles in Scala‘ also taught byContinue Reading

Scala Cookbook: Tail recursive factorial

The direct port of a human readable description of the factorial algorithm may look as follows. However – this isn’t tail recursive and will fail for large inputs. Exception in thread “main” java.lang.StackOverflowError at java.math.BigInteger.getInt( The classic nested accumulator helper function idiom can be used to make this tail recursive. So what’s going on here?Continue Reading

Scala Cookbook: Pattern matching on BigInt

Let’s take the factorial algorithm as an example. One might expect to convert this into a pattern matched equivalent as follows. In fact this will give you the error below. type mismatch; found : Int(0) required: BigInt Factorial.scala The reason is that BigInt is not a case class and does not have an unapply() methodContinue Reading