Setting BOOT_RTJAR: rt.jar vs. 'sun.boot.class.path'

[Erik Joelsson]

Hello Volker,

I like this solution, even if it could be viewed as a bit of overkill.

/Erik

On 2013-11-14 17:35, Volker Simonis wrote:
> Hi,
>
> I wanted to solve "8026964: Building with an IBM J9 boot jdk requires
> special settings for BOOT_RTJAR"
> (https://bugs.openjdk.java.net/browse/JDK-8026964) and came across the
> question what the real semantics of BOOT_RTJAR is?
>
> Currently, for OpenJDK/Oracle based boot JDKs BOOT_RTJAR is simply set
> to "rt.jar" (and for MacOSX to "classes.jar" if "rt.jar" is not
> found). For an IBM J9 boot JDK however this is not so easy because
> some essential classes (like Object or String) are not contained in
> "rt.jar" (see the before mentioned bug for more details). So for IBM
> J9 we need to add additional jar-files to BOOT_RTJAR.
>
> Now I wonder what's the exact semantics of BOOT_RTJAR i.e. which are
> the required classes it should contain? Naively I would assume these
> are the classes contained in the "sun.boot.class.path" system
> property. But for an OpenJDK/Oracle based JDK, this property contains
> much more classes than just rt.jar:
>
> sun.boot.class.path= \
>   <jdk_root>/jre/lib/resources.jar \
>   <jdk_root>/jre/lib/rt.jar \
>   <jdk_root>/jre/lib/sunrsasign.jar \
>   <jdk_root>/jre/lib/jsse.jar \
>   <jdk_root>/jre/lib/jce.jar \
>   <jdk_root>/jre/lib/charsets.jar \
>   <jdk_root>/jre/lib/jfr.jar \
>   <jdk_root>/jre/classes
>
>
> The Oracle documentation I could find ("How Classes are Found" at
> http://docs.oracle.com/javase/7/docs/technotes/tools/findingclasses.html)
> states: "...Bootstrap classes are the classes that implement the Java
> 2 Platform. Bootstrap classes are in the rt.jar and several other jar
> files in the jre/lib directory. These archives are specified by the
> value of the bootstrap class path which is stored in the
> sun.boot.class.path system property..."
>
> So for me it seems that the current solution of using just "rt.jar"
> works only accidentally until now and it would be more logical to set
> BOOT_RTJAR to the value of "sun.boot.class.path". This value could be
> queried during the configure process (e.g. by using the -XshowSettings
> option). As far as I can see '-XshowSettings' and the
> "sun.boot.class.path" property is supported on all the JDKs I know
> (OpenJDK, Oracle JDK, SAP JVM, IBM J9, HP JVM).
>
> So my question is, if there are any objectives if I'd change the
> current BOOT_RTJAR detection to the following lines:
>
>    # Parse the settings of the 'sun.boot.class.path' property
>    # The tricky thing is that we must quote AWK field references (i.e.
> $1, $2, ..)
>    # and the name 'index' which is a M4-buildin function by placing brackets
>    # (i.e. '[]') into the corresponding names.
>    BOOT_RTJAR=`$BOOT_JDK/bin/java -XshowSettings 2>&1 | $NAWK ' \
>        /path.separator/      { path_separator = $[]3} \
>        /sun.boot.class.path/ { sun_boot_class_path = $[]3; \
>                                while (getline && !in[]dex($[]0,"=")) { \
>                                  sun_boot_class_path =
> sun_boot_class_path "\n" $[]1 \
>                                } \
>                              } \
>        END { gsub("\n", path_separator, sun_boot_class_path); print
> sun_boot_class_path }'`
>
> which effectively set BOOT_RTJAR to the value of 'sun.boot.class.path'
> (separated by the valid platform path separator which is also queried
> from the output of '-XshowSettings').
>
> I've tested this and it works on Linux and Solaris with an OppenJDK
> based boot JDK and on AIX with the IBM J9 boot JDK. I think it would
> be more robust for other JDKs as well. And of course it fixes my bug:)
>
> So if there are no general objections I'll be happy to prepare a
> formal webrev for this issue.
>
> Regards,
> Volker