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Re: [fedora-java] Re: ld doesn't know about location of libjvm Thomas Fitzsimmons Fri Nov 03 12:04:14 2006

Braden McDaniel wrote:
Thomas Fitzsimmons wrote:
Hi,

Braden McDaniel wrote:
On Sun, 29 Oct 2006 14:21:29 -0500, Thomas Fitzsimmons wrote:

Hi,

Braden McDaniel wrote:
ld seems not to know about /usr/lib[64]/gcj-4.1.1; and as such cannot find libjvm.so without a -L flag. Is this deliberate or a bug?
This is deliberate. You should be dlopen'ing libjvm.so rather than linking to it directly. To locate it, use $JAVA_HOME/jre/lib/i386/client/libjvm.so like you would on other JVMs. java-1.4.2-gcj-compat symlinks /usr/lib/jvm/java/jre/lib/i386/client/libjvm.so to libgcj's libjvm implementation.

Fair enough; but I don't want to force my users to set JAVA_HOME. Is this
prefix build-time discoverable?

If you're willing to require GCJ's implementation then you can count on libjvm.so being located at:

/usr/lib/jvm/java-1.4.2-gcj/jre/lib/$arch/client/libjvm.so

On recent Fedora, perhaps; but I'm inclined not to depend on the java-1.4.2-gcj-compat in general since I don't know how widely it's coupled to gcj deployments.

I think fairly widely: recent Debian, Ubuntu and Fedora at least. I think the above libjvm.so location is fairly reliable, if you ensure that your application package puts a packaging system requirement on java-gcj-compat (e.g. Requires: java-gcj-compat).

For FC-7 my plan is to merge java-1.4.2-gcj-compat completely into libgcj so that this distinction will not exist for subsequent releases.


What I'd like to support is preference for the libjvm relative to JAVA_HOME at run-time; but falling back to a location established for libjvm at build-time (if JAVA_HOME is not set at run-time).

where $arch is the rpm architecture string. To print this string for the target system, use:

rpm --eval "%{_arch}"

Not a solution for systems that aren't RPM-based. (But not a problem for me; autoconf solves this.)

If you'd like to require any JPackage JRE then the architecture string may be a little different (e.g., amd64 vs. x86_64) but the location will be:

/usr/lib/jvm/jre/lib/$arch/client/libjvm.so

If you'd like to support other types of JDK installations like /opt or /usr/java then you'll have to do a runtime search.

It's looking like my best option is to eke out all the information I can from libgcj.pc. Assuming libjvm.so is reliably installed in ${libdir}/gcj-${gcj_version} across distributions, I should be able to get what I need from it.

The problem with this approach is that this directory is versioned. So if you hard-code /usr/lib/gcj-4.1.1 into your application, it will break when the user upgrades to gcj 4.1.2. You could do a search for /usr/lib*/gcj-*, but this is something that java-gcj-compat is intended to do for you; it always keeps its unversioned libjvm.so symlink pointing to the right place.

Tom

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