Saint's Log

Trial Division Factorization Disassembly

When Experimenting with Async Profiler, I created a basic trial division factorization Java application. To run it, download the OpenJDK build if it isn’t already installed:

mkdir -p ~/java/binaries/jdk/x64
cd ~/java/binaries/jdk/x64
wget https://aka.ms/download-jdk/microsoft-jdk-17.0.7-linux-x64.tar.gz
tar xzf microsoft-jdk-17.0.7-linux-x64.tar.gz

Test the factorization application to verify that the Java build works.

export JAVA_HOME=~/java/binaries/jdk/x64/jdk-17.0.7+7

cd ~/repos/scratchpad/demos/java/FindPrimes
$JAVA_HOME/bin/javac Factorize.java
$JAVA_HOME/bin/java Factorize 123890571352112309857

# Use 4 threads to speed things up
$JAVA_HOME/bin/java Factorize 123890571352112309857 CUSTOM_THREAD_COUNT_VIA_THREAD_CLASS 4

Using hsdis

hsdis is a HotSpot plugin for disassembling dynamically generated code. Chriswhocodes was kind enough to build hsdis for various platforms and share the binaries on his website – hsdis HotSpot Disassembly Plugin Downloads (chriswhocodes.com). Download the appropriate hsdis binary and move it to the OpenJDK build’s lib directory, e.g.

wget https://chriswhocodes.com/hsdis/hsdis-amd64.so
export JAVA_HOME=~/java/binaries/jdk/x64/jdk-17.0.7+7
mv hsdis-amd64.so $JAVA_HOME/lib/

ls -l $JAVA_HOME/bin/hsdis*

We will need the PrintAssembly option to disassemble the code generated by the compiler when running a Java program. This option requires diagnostic VM options to be unlocked. This is the full command line for generating the disassembly from the application’s execution. The output is redirected to a code.asm file since it can be voluminous.

$JAVA_HOME/bin/java -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly Factorize 123890571352112309857 CUSTOM_THREAD_COUNT_VIA_THREAD_CLASS 4 > code.asm

Here is a snippet of the disassembly in code.asm:

============================= C1-compiled nmethod ==============================
----------------------------------- Assembly -----------------------------------

Compiled method (c1)    2052  266       2       java.math.BigInteger::implMulAdd (81 bytes)
 total in heap  [0x00007f2e5943ca90,0x00007f2e5943d038] = 1448
 relocation     [0x00007f2e5943cbf0,0x00007f2e5943cc28] = 56
 main code      [0x00007f2e5943cc40,0x00007f2e5943ce00] = 448
 stub code      [0x00007f2e5943ce00,0x00007f2e5943ce30] = 48
 metadata       [0x00007f2e5943ce30,0x00007f2e5943ce38] = 8
 scopes data    [0x00007f2e5943ce38,0x00007f2e5943cee0] = 168
 scopes pcs     [0x00007f2e5943cee0,0x00007f2e5943d010] = 304
 dependencies   [0x00007f2e5943d010,0x00007f2e5943d018] = 8
 nul chk table  [0x00007f2e5943d018,0x00007f2e5943d038] = 32

--------------------------------------------------------------------------------
[Constant Pool (empty)]

--------------------------------------------------------------------------------

[Verified Entry Point]
  # {method} {0x00000008000a47c0} 'implMulAdd' '([I[IIII)I' in 'java/math/BigInteger'
  # parm0:    rsi:rsi   = '[I'
  # parm1:    rdx:rdx   = '[I'
  # parm2:    rcx       = int
  # parm3:    r8        = int
  # parm4:    r9        = int
  #           [sp+0x50]  (sp of caller)
  0x00007f2e5943cc40:   mov    %eax,-0x14000(%rsp)
  0x00007f2e5943cc47:   push   %rbp
  0x00007f2e5943cc48:   sub    $0x40,%rsp
  0x00007f2e5943cc4c:   movabs $0x7f2e38075370,%rax
  0x00007f2e5943cc56:   mov    0x8(%rax),%edi
  0x00007f2e5943cc59:   add    $0x2,%edi
  0x00007f2e5943cc5c:   mov    %edi,0x8(%rax)
  0x00007f2e5943cc5f:   and    $0xffe,%edi
  0x00007f2e5943cc65:   cmp    $0x0,%edi
  0x00007f2e5943cc68:   je     0x00007f2e5943cd52           ;*iload {reexecute=0 rethrow=0 return_oop=0}
                                                            ; - java.math.BigInteger::implMulAdd@0 (line 3197)
  0x00007f2e5943cc6e:   movslq %r9d,%r9
  0x00007f2e5943cc71:   movabs $0xffffffff,%rax
  0x00007f2e5943cc7b:   and    %rax,%r9
...

Finding the Java Installation Path

In the above example, I have used a Java build in a custom path. If you are using a Java build that is already installed, then a few extra steps might be needed to determine where the JAVA_HOME path, e.g.

saint@ubuntuvm:~$ which java
/usr/bin/java
saint@ubuntuvm:~$ ls -l `which java`
saint@ubuntuvm:~$ ls -l /etc/alternatives/java