How Can I Inspect JIT-Compiled Java Code?

Inspecting JIT-Compiled Code in the JVM

Accessing JIT Output

To view the native code generated by the JIT compiler in a Java Virtual Machine (JVM), employ the following JVM options:

-XX:+UnlockDiagnosticVMOptions
-XX:+PrintAssembly

Filtering on Specific Methods

Alternatively, you can filter on a particular method using the syntax:

-XX:+UnlockDiagnosticVMOptions
-XX:CompileCommand=print,*MyClass.myMethod

Windows Considerations

For Windows users, you must first install hsdis-amd64.dll and hsdis-i386.dll from the fcml project.

Step-by-Step Installation Guide for Windows

1. Install Cygwin and select the following packages:

   • make
   • mingw64-x86_64-gcc-core (for hsdis-amd64.dll)
   • mingw64-i686-gcc-core (for hsdis-i386.dll)
   • diffutils (from the Utils category)
2. Download and extract the GNU binutils source package to your Cygwin home directory (e.g., C:cygwinhome<username>).
3. Download and extract the OpenJDK hsdis directory to your Cygwin home directory.
4. Navigate to the hsdis directory in the Cygwin Terminal (cd ~/hsdis).

5. Compile hsdis-amd64.dll:

   • make OS=Linux MINGW=x86_64-w64-mingw32 'AR=$(MINGW)-ar' BINUTILS=~/binutils-2.25

6. Compile hsdis-i386.dll:

   • make OS=Linux MINGW=i686-w64-mingw32 'AR=$(MINGW)-ar' BINUTILS=~/binutils-2.25
7. Edit ~/hsdis/build/Linux-amd64/bfd/Makefile and change SUBDIRS = doc po to SUBDIRS = po.
8. Re-run the compilation command.

9. Copy the DLL to your JRE's bin directory:

   • Copy from hsdisbuildLinux-amd64 or hsdisbuildLinux-i586 to JREbinserver or JREbinclient.

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