Hi Andrew,
Whether or not the jsr instruction is used is -target specific; version
50.0 class files from -target 6 and later do not support jsr/ret since
stackmaps are used.
I haven't delved into the OpenJDK 6 build before writing this email, but
I suspect some of the classes in rt.jar are compiled with -target 5, but
javac in OpenJDK 6 defaults to -target 6 so you wouldn't see jsr
instructions from a stock compile.
Sufficiently recent versions of javap will emit the classfile version
under the -verbose flag.
HTH,
-Joe
[1] "Source, target, class file version decoder ring,"
http://blogs.oracle.com/darcy/entry/source_target_class_file_version
On 02/02/2012 04:46 AM, Andrew Haley wrote:
I'm sorry for the cross-post, but I don't know exactly who to
address this to.
Just to save you time reading all this: the javac in OpenJDK 6
generates jsr instructions, but only if you compile a great many
source files in one go. This affects rt.jar. I'm trying to find
out why.
If you build OpenJDK6 and do this:
happy:jdk6 $ javap -c -bootclasspath build/linux-amd64/classes/ -classpath
build/linux-amd64/classes/ java.util.concurrent/PriorityBlockingQueue | grep jsr
48: jsr 62
56: jsr 62
17: jsr 28
23: jsr 28
74: jsr 87
...
you'll see lots of jsr instructions. Why is this? It seems that if
you compile the .java file this doesn't happen:
happy:jdk6 $ ./build/linux-amd64/j2sdk-image/jre/bin/java -Xmx896m -Xms128m
-XX:PermSize=32m -XX:MaxPermSize=160m
-Xbootclasspath/p:./build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar
-jar ./build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar -g -source 1.5
-target 5 -encoding ascii
-Xbootclasspath:/local/openjdk/jdk6/build/linux-amd64/classes -sourcepath
/local/openjdk/jdk6/build/linux-amd64/gensrc:/local/openjdk/jdk6/jdk/src/solaris/classes:/local/openjdk/jdk6/jdk/src/share/classes
-d /tmp
/local/openjdk/jdk6/jdk/src/share/classes/java/util/concurrent/PriorityBlockingQueue.java
happy:jdk6 $ javap -c -bootclasspath /tmp -classpath /tmp
java.util.concurrent/PriorityBlockingQueue | grep jsr
No jsr instructions this time.
So, I try the compile again, but with the full list of classes in .classes.list:
$ $ /local/openjdk/jdk6/build/linux-amd64/j2sdk-image/jre/bin/java -Xmx896m
-Xms128m -XX:PermSize=32m -XX:MaxPermSize=160m
-Xbootclasspath/p:/local/openjdk/jdk6/build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar
-jar
/local/openjdk/jdk6/build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar -g
-source 1.5 -target 5 -encoding ascii
-Xbootclasspath:/local/openjdk/jdk6/build/linux-amd64/classes -sourcepath
/local/openjdk/jdk6/build/linux-amd64/gensrc:/local/openjdk/jdk6/jdk/src/solaris/classes:/local/openjdk/jdk6/jdk/src/share/classes
-d /tmp
@/local/openjdk/jdk6/build/linux-amd64/tmp/java/java.lang/java/.classes.list
$ javap -c -bootclasspath /tmp -classpath /tmp
java.util.concurrent/PriorityBlockingQueue | grep jsr | head -5
48: jsr 62
56: jsr 62
17: jsr 28
23: jsr 28
74: jsr 87
Lots of jsrs.
Now the really weird bit: if I edit classes.list to contain only a
small subset of the files and run the command again,
$ grep java.util.concurrent
/local/openjdk/jdk6/build/linux-amd64/tmp/java/java.lang/java/.classes.list>
classes.concurrent
$ /local/openjdk/jdk6/build/linux-amd64/j2sdk-image/jre/bin/java -Xmx896m
-Xms128m -XX:PermSize=32m -XX:MaxPermSize=160m
-Xbootclasspath/p:/local/openjdk/jdk6/build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar
-jar
/local/openjdk/jdk6/build/linux-amd64/langtools/dist/bootstrap/lib/javac.jar -g
-source 1.5 -target 5 -encoding ascii
-Xbootclasspath:/local/openjdk/jdk6/build/linux-amd64/classes -sourcepath
/local/openjdk/jdk6/build/linux-amd64/gensrc:/local/openjdk/jdk6/jdk/src/solaris/classes:/local/openjdk/jdk6/jdk/src/share/classes
-d /tmp @classes.concurrent
$ javap -c -bootclasspath /tmp -classpath /tmp
java.util.concurrent/PriorityBlockingQueue | grep jsr | head -5
... no jsr instructions.
I realize that OpenJDK 6 is nearing EOL, but this behaviour is so bizarre
that I'd appreciate some input!
Thanks,
Andrew.
