inspecting hotspot code using gdb

[Tom Rodriguez]

Using a debugger with the java launcher can be a little tricky since it normally 
sets up the LD_LIBRARY_PATH and relaunches the VM to select the right libjvm.so 
which makes debuggers unhappy.  libjvm.so is also dynamically loaded so they 
symbols won't be available until you've at least run it once.  Your 
LD_LIBRARY_PATH should be set to the value of the java.library.path property 
from the VM you want to run.  gdb will get into various bad states if you don't 
do this part.  Also by default you also want to suppress a lot of signals that 
the JVM uses.

I attached the script I use for launching the VM under a debugger.  It works for 
dbx and gdb and has a little Java class for getting the java.library.path 
property from a VM.  You just prefix dbxr onto the full command line you want to 
debug and it sets everything up for you.  The script is a little ugly and has 
some special bits to deal with getting properties from a JVM which might be at 
least a little broken.  Obviously if you are trying to debug a JVM which won't 
even boot then it will be hard to get properties from it.  It's possible to 
derive the proper LD_LIBRARY_PATH setting from the location of the JDK but that 
was error prone enough that I switched to using a class to read it out.  Anyway, 
hopefully it will be useful.

tom

Ben Cheng wrote:
> Hello,
> 
> I tried to set a breakpoint in a Hotspot function, say 
> "ciEnv::register_method", under gdb, but gdb couldn't seem to find the 
> symbols. I am using my locally built libjvm.so so symbols should be 
> there, so I am thinking that feeding the java launcher to gdb is the 
> wrong thing to do here.
> 
> Can someone explain the procedures to debug hotspot under gdb?
> 
> Thanks,
> -Ben
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