I've been compiling Sun/Oracle Java 1.6.0_23 with gcc 4.5.1 and 4.6.0 to see if a) it can be done (it can) and b) if there are any performance improvements to be made (dubious). One of the things that I have tried is using LTO on the resulting files. 

With gcc 4.6.0 20110115, this mostly works until I try to add -flto to the link that creates libjvm.so. Using binutils from cvs head, this fails to link with about 20 pages of undefined references. There was a patch posted to the gcc mailing list recently with the subject "PATCH: 2 stage BFD linker for LTO plugin" and applying this to binutils does help immensely - it reduces the undefined references from ~20 pages down to 13 individual items. However, it uses ~5.7GB of my 4GB RAM and takes about 12 hours to link. A non-lto link of the same items appears to use ~700MB RAM and takes a second or two.

The problematic command generated by the build process is

/usr/local/gcc46/bin/gcc -m64 -Xlinker -O1   -shared -Xlinker --version-script=mapfile_reorder -Xlinker -soname=libjvm.so -static-libgcc -o libjvm.so abstractCompiler.o accessFlags.o ad_x86_64.o ad_x86_64_clone.o ad_x86_64_expand.o ad_x86_64_format.o ad_x86_64_gen.o ad_x86_64_misc.o ad_x86_64_peephole.o ad_x86_64_pipeline.o adaptiveSizePolicy.o addnode.o adjoiningGenerations.o adjoiningVirtualSpaces.o ageTable.o allocation.o allocationStats.o aprofiler.o arguments.o array.o arrayKlass.o arrayKlassKlass.o arrayOop.o asPSOldGen.o asPSYoungGen.o asParNewGeneration.o assembler.o assembler_linux_x86.o assembler_x86.o atomic.o attachListener.o attachListener_linux.o barrierSet.o bcEscapeAnalyzer.o biasedLocking.o binaryTreeDictionary.o bitMap.o block.o blockOffsetTable.o buildOopMap.o bytecode.o bytecodeHistogram.o bytecodeInfo.o bytecodeInterpreter.o bytecodeInterpreterWithChecks.o bytecodeInterpreter_x86.o bytecodeStream.o bytecodeTracer.o bytecodes.o bytecodes_x86.o c2_globals.o c2_init_x86.o c2compiler.o cSpaceCounters.o callGenerator.o callnode.o cardTableExtension.o cardTableModRefBS.o cardTableRS.o cfgnode.o chaitin.o chaitin_linux.o ciArray.o ciArrayKlass.o ciCPCache.o ciCallSite.o ciConstant.o ciConstantPoolCache.o ciEnv.o ciExceptionHandler.o ciField.o ciFlags.o ciInstance.o ciInstanceKlass.o ciInstanceKlassKlass.o ciKlass.o ciKlassKlass.o ciMethod.o ciMethodBlocks.o ciMethodData.o ciMethodHandle.o ciMethodKlass.o ciNullObject.o ciObjArray.o ciObjArrayKlass.o ciObjArrayKlassKlass.o ciObject.o ciObjectFactory.o ciSignature.o ciStreams.o ciSymbol.o ciSymbolKlass.o ciType.o ciTypeArray.o ciTypeArrayKlass.o ciTypeArrayKlassKlass.o ciTypeFlow.o ciUtilities.o classFileError.o classFileParser.o classFileStream.o classLoader.o classLoadingService.o classes.o classify.o cmsAdaptiveSizePolicy.o cmsCollectorPolicy.o cmsGCAdaptivePolicyCounters.o cmsLockVerifier.o cmsPermGen.o coalesce.o codeBlob.o codeBuffer.o codeCache.o collectedHeap.o collectionSetChooser.o collectorCounters.o collectorPolicy.o compactibleFreeListSpace.o compactingPermGenGen.o compilationPolicy.o compile.o compileBroker.o compileLog.o compiledIC.o compiledICHolderKlass.o compiledICHolderOop.o compilerOracle.o compressedStream.o concurrentG1Refine.o concurrentG1RefineThread.o concurrentGCThread.o concurrentMark.o concurrentMarkSweepGeneration.o concurrentMarkSweepThread.o concurrentMarkThread.o concurrentZFThread.o connode.o constMethodKlass.o constMethodOop.o constantPoolKlass.o constantPoolOop.o constantTag.o copy.o cpCacheKlass.o cpCacheOop.o cppInterpreter.o cppInterpreter_x86.o debug.o debugInfo.o debugInfoRec.o debug_x86.o defNewGeneration.o deoptimization.o depChecker_x86.o dependencies.o dfa_x86_64.o dict.o dictionary.o dirtyCardQueue.o disassembler.o divnode.o doCall.o domgraph.o dtraceAttacher.o dtraceJSDT.o dtraceJSDT_linux.o dump.o dump_x86_64.o escape.o events.o evmCompat.o exceptionHandlerTable.o exceptions.o fieldDescriptor.o fieldType.o filemap.o forte.o fprofiler.o frame.o frame_x86.o freeBlockDictionary.o freeChunk.o freeList.o g1BlockOffsetTable.o g1CollectedHeap.o g1CollectorPolicy.o g1MMUTracker.o g1MarkSweep.o g1MemoryPool.o g1RemSet.o g1SATBCardTableModRefBS.o g1_globals.o gSpaceCounters.o gcAdaptivePolicyCounters.o gcCause.o gcLocker.o gcPolicyCounters.o gcStats.o gcTaskManager.o gcTaskThread.o gcUtil.o gcm.o genCollectedHeap.o genMarkSweep.o genRemSet.o generateOopMap.o generateOptoStub.o generation.o generationCounters.o generationSpec.o globalDefinitions.o globals.o graphKit.o growableArray.o handles.o hashtable.o heap.o heapDumper.o heapInspection.o heapRegion.o heapRegionRemSet.o heapRegionSeq.o histogram.o hpi.o hpi_linux.o icBuffer.o icBuffer_x86.o icache.o icache_x86.o idealKit.o ifg.o ifnode.o immutableSpace.o indexSet.o init.o instanceKlass.o instanceKlassKlass.o instanceOop.o instanceRefKlass.o intHisto.o interfaceSupport.o interp_masm_x86_64.o interpreter.o interpreterRT_x86_64.o interpreterRuntime.o interpreter_x86_64.o invocationCounter.o iterator.o java.o javaAssertions.o javaCalls.o javaClasses.o jni.o jniCheck.o jniFastGetField.o jniFastGetField_x86_64.o jniHandles.o jniPeriodicChecker.o jvm.o jvm_linux.o jvmtiClassFileReconstituter.o jvmtiCodeBlobEvents.o jvmtiEnter.o jvmtiEnterTrace.o jvmtiEnv.o jvmtiEnvBase.o jvmtiEnvThreadState.o jvmtiEventController.o jvmtiExport.o jvmtiExtensions.o jvmtiGetLoadedClasses.o jvmtiImpl.o jvmtiManageCapabilities.o jvmtiRedefineClasses.o jvmtiTagMap.o jvmtiThreadState.o jvmtiTrace.o jvmtiUtil.o klass.o klassKlass.o klassOop.o klassVtable.o lcm.o library_call.o linkResolver.o live.o loaderConstraints.o location.o locknode.o loopTransform.o loopUnswitch.o loopnode.o loopopts.o lowMemoryDetector.o machnode.o macro.o management.o markOop.o markSweep.o matcher.o memRegion.o memnode.o memoryManager.o memoryPool.o memoryService.o memprofiler.o methodComparator.o methodDataKlass.o methodDataOop.o methodHandleWalk.o methodHandles.o methodHandles_x86.o methodKlass.o methodLiveness.o methodOop.o monitorChunk.o mulnode.o multnode.o mutableNUMASpace.o mutableSpace.o mutex.o mutexLocker.o mutex_linux.o nativeInst_x86.o nativeLookup.o nmethod.o node.o numberSeq.o objArrayKlass.o objArrayKlassKlass.o objArrayOop.o objectMonitor_linux.o objectStartArray.o oop.o oopFactory.o oopMap.o oopMapCache.o oopRecorder.o oopsHierarchy.o opcodes.o orderAccess.o os.o osThread.o osThread_linux.o os_linux.o os_linux_x86.o ostream.o output.o parCardTableModRefBS.o parGCAllocBuffer.o parMarkBitMap.o parNewGeneration.o parallelScavengeHeap.o parse1.o parse2.o parse3.o parseHelper.o pcDesc.o pcTasks.o perf.o perfData.o perfMemory.o perfMemory_linux.o permGen.o phase.o phaseX.o placeholders.o port.o postaloc.o preserveException.o privilegedStack.o promotionInfo.o psAdaptiveSizePolicy.o psCompactionManager.o psGCAdaptivePolicyCounters.o psGenerationCounters.o psMarkSweep.o psMarkSweepDecorator.o psMemoryPool.o psOldGen.o psParallelCompact.o psPermGen.o psPromotionLAB.o psPromotionManager.o psScavenge.o psTasks.o psVirtualspace.o psYoungGen.o ptrQueue.o referencePolicy.o referenceProcessor.o reflection.o reflectionUtils.o reg_split.o regalloc.o register.o register_definitions_x86.o register_x86.o regmask.o relocInfo.o relocInfo_x86.o relocator.o resolutionErrors.o resourceArea.o restore.o rewriter.o rframe.o rootnode.o runtime.o runtimeService.o runtime_x86_64.o safepoint.o satbQueue.o scopeDesc.o serialize.o set.o sharedHeap.o sharedRuntime.o sharedRuntimeTrans.o sharedRuntimeTrig.o sharedRuntime_x86_64.o signature.o sizes.o space.o spaceCounters.o spaceDecorator.o sparsePRT.o specialized_oop_closures.o split_if.o stackMapFrame.o stackMapTable.o stackValue.o stackValueCollection.o statSampler.o stringopts.o stubCodeGenerator.o stubGenerator_x86_64.o stubRoutines.o stubRoutines_linux.o stubRoutines_x86_64.o stubs.o subnode.o superword.o survRateGroup.o sweeper.o symbolKlass.o symbolOop.o symbolTable.o synchronizer.o systemDictionary.o task.o taskqueue.o templateInterpreter.o templateInterpreter_x86_64.o templateTable.o templateTable_x86_64.o tenuredGeneration.o thread.o threadCritical_linux.o threadLS_linux_x86.o threadLocalAllocBuffer.o threadLocalStorage.o threadService.o thread_linux_x86.o timer.o type.o typeArrayKlass.o typeArrayKlassKlass.o typeArrayOop.o unhandledOops.o universe.o unsafe.o utf8.o vectornode.o vectset.o verificationType.o verifier.o vframe.o vframeArray.o vframe_hp.o virtualspace.o vmCMSOperations.o vmError.o vmError_linux.o vmGCOperations.o vmPSOperations.o vmStructs.o vmSymbols.o vmThread.o vm_operations.o vm_operations_g1.o vm_version.o vm_version_linux_x86.o vm_version_x86.o vmreg.o vmreg_x86.o vtableStubs.o vtableStubs_x86_64.o workgroup.o xmlstream.o yieldingWorkgroup.o idealGraphPrinter.o  linux_x86_64.o -Wl,-Bstatic -lstdc++ -Wl,-Bdynamic -lm -ldl -lpthread -flto  -fuse-linker-plugin

Retrieving that command and removing "-flto  -fuse-linker-plugin" and rerunning it allows the link to complete and generate a libjvm.so that has no undefined references (beyond those expected in external .so files).

The undefined external references listed by the LTO version of the same command are

/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void G1ParPushHeapRSClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void FilterOutOfRegionClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void FilterAndMarkInHeapRegionAndIntoCSClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void HRInto_G1RemSet::write_ref_nv<unsigned int>(HeapRegion*, unsigned int*)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void FilterIntoCSClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void UpdateRSetImmediate::do_oop_work<unsigned int>(unsigned int*)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void FilterInHeapRegionAndIntoCSClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void UpdateRSetImmediate::do_oop_work<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void UpdateRSOopClosure::do_oop_work<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void UpdateRSOopClosure::do_oop_work<unsigned int>(unsigned int*)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void G1ParScanClosure::do_oop_nv<oopDesc*>(oopDesc**)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `HeapRegionSeq::addr_to_region(void const*)'
/sources/java/control/build/linux-amd64/hotspot/outputdir/linux_amd64_compiler2/product/libjvm.so: undefined reference to `void HRInto_G1RemSet::write_ref_nv<oopDesc*>(HeapRegion*, oopDesc**)'