How Can I View JIT-Compiled Code in the Java Virtual Machine (JVM)?

Viewing JIT-Compiled Code in Java Virtual Machine (JVM)

The Java Virtual Machine (JVM) features a Just-In-Time (JIT) compiler that optimizes Java bytecode into native code. To examine this native code, consider the following techniques:

General Usage

Utilize JVM options as follows:

-XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly

Specific Method Filtering

You can isolate specific methods using the following syntax:

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

Note:

• Quotes may be necessary around the second argument, depending on the OS.
• Method inlining may hinder observability of certain optimizations.

Installation on Windows

For Windows systems, follow the instructions below to build and install required libraries:

Prebuilt Binaries

Download prebuilt binaries for Windows from the fcml project:

• hsdis-amd64.dll
• hsdis-i386.dll

Manual Building

1. Install Cygwin with the following packages:

   • make
   • mingw64-x86_64-gcc-core (for hsdis-amd64.dll)
   • mingw64-i686-gcc-core (for hsdis-i386.dll)
   • diffutils
2. Extract the GNU binutils source package (e.g., binutils-2.25.tar.bz2) to your Cygwin home directory.
3. Extract the OpenJDK hsdis directory (from srcsharetools) to your Cygwin home directory.
4. In Cygwin Terminal, navigate to ~/hsdis.
5. Build hsdis-amd64.dll (or hsdis-i386.dll) using the appropriate command:

make OS=Linux MINGW=x86_64-w64-mingw32 'AR=$(MINGW)-ar' BINUTILS=~/binutils-2.25
(or)
make OS=Linux MINGW=i686-w64-mingw32 'AR=$(MINGW)-ar' BINUTILS=~/binutils-2.25

6. Edit hsdisbuildLinux-amd64bfdMakefile and change SUBDIRS = doc po to SUBDIRS = po.
7. Re-run the build command.
8. Copy the built DLL to your JRE's binserver or binclient directory.

Additional Tips

For Intel ASM syntax, use the option -XX:PrintAssemblyOptions=intel alongside the PrintAssembly options.

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