Question about java probe

[Shuxin Yang <shuxinyang dot oss at gmail dot com>]

Hi, There:

  I have bunch of questions about java probe. The stap I'm using is 
built from the most recent release without any special flags.Tons thanks 
in advance for the help!

  Q1: I find an example here: 
https://developers.redhat.com/blog/2014/01/10/probing-java-w-systemtap/

        The statement 'printf("hit ... %d\n", $arg1)' print a wrong 
value. However, if I change this statement to 'printf("hit ... %s\n", 
arg1)', then it works. Why so?

  Q2: follow the example in Q1. What if the function being probed has a 
non-primitive typed parameter. Say argument foo of type Foo. Is it 
possible to access foo's data member, or call its member function.

  Q3: Look like print_java_stack() only prints the stack of the thread 
in question; It does *not* print all threads' stack. Am I right?

  Q4: How to print java stack when a system call is hit? I try to call 
print_java_stack() inside system call probe function, and get nothing. 
Should I call other function? Or it's impossible for now? If this is the 
case, is it possible to hack the systemtap to take advantage of the 
perf-jit support (https://lwn.net/Articles/633846/) to print the java 
stack of JIT-ed code?

Thanks

Shuxin