How to debug HotSpot

[=?GBK?B?t7nNsA==?=]

 Hi all,
I need you guys' help. I'm reading and learning details in Hotspot, especially garbage collector. But I'm trapped in debug and trace hotspot itselp.

I have built hotspot in ubuntu 12.04 and entered gdb mode with "hotspot -gdb ....". But as libjvm.so is loaded at runtime, I can't step into that part in gdb. Is there any way to step into libjvm.so?

Besides, here is how I build hotspot. Just check if there are some additional building parameters.
LANG=C ALT_BOOTDIR=/usr/lib/jvm/java-6-openjdk/ HOTSPOT_BUILD_JOBS=5 ARCH_DATA_MODEL=64 ALT_OUTPUTDIR=../../build/hotspot_debug make jvmg jvmg1 2>&1 | tee ../../build/hotspot_debug

Thanks
Arthur