OpenJDK Hacking Workshop -- Insructions

Participants will need an x86 machine running some version of Linux
(virtualized should be ok). fedora 17/18/19 is recommended. Other
Linuxes will probably work so long as you are happy and willing to
install missing packages or upgrade package versions as determined by
the configure script.

See the download instructions for help on obtaining the OpenJDK source
code forest.

See the build instructions for help bulding OpenJDK
forest.

Step 1:

Run your OpenJDK build from the command line

1) Move to the location where you downloadeded the code

$ cd <base_dir_of_your_choice>

2) run javac on Hello.java (you will need to write Hello.java)

$ ./build/linux-x86_64-normal-server-slowdebug/images/j2sdk-image/bin/javac Hello.java

3) run Hello

$ ./build/linux-x86_64-normal-server-slowdebug/images/j2sdk-image/bin/java Hello

Step 2:

Now try running with some of the debug/trace options available in
runtime/globals.hpp enabled

Watch as the JDK calls out to JVM_ENTRY functions

-XX:+TraceJVMCalls

Watch as the JVM calls out to runtime support functions

-XX:+TraceRuntimeCalls

Dump the generated templates used by th etemplate interpreter

-XX:+PrintInterpreter

Show what the compiler is doing:

-- print each compile request queued to the compiler

-XX:+CIPrintRequests

-- print details of each method compile

-XX:+PrintCompilation

-- trace installation of each compiled method

-XX:TraceNMethodInstalls

hmm, this one can get quite verbose unless you use it with CompileOnly
(see below)

Print disassembly of compiled methods

-XX:+PrintNMethods

limit what gets compiled

-Xcomp -XX:+PrintCompilation -XX:CompileOnly="Hello.main"

limit compilation and dump the compiled code

-Xcomp -XX:+PrintCompilation -XX:CompileCommand=compileonly,"Hello.main"

-Xcomp -XX:+PrintCompilation -XX:CompileCommand=compileonly,"Hello.main" -XX:CompileCommand=print,"Hello.main"

specify multiple commands via a command file

cat > commands << EOF
compileonly Hello.main
print Hello.main
compileonly java/lang/String.hashCode
print java/lang/String.hashCode
EOF

-Xcomp -XX:+PrintCompilation -XX:CompileCommandFile=commands

disable tiered compilation

-XX:-TieredCompilation (default is yes)

(if you want to up the detail for a trace/print option)

-XX:+Verbose

for even more detail 

-XX:+WizardMode

Step 5

Now run in gdb (best is within emacs!)

$ gdb ./build/linux-x86_64-normal-server-slowdebug/images/j2sdk-image/bin/java
(gdb) break TemplateInterpreter::initialize
 . . .
(gdb) run Hello