put probes on a specific line

[Li Guanglei <guanglei@cn.ibm.com>]

Hi,

   I ever thought that kernel.function("*@kernel/signal.c:734") will 
put a probe on line 734. But after testing and reading the stapprobes 
man page, that actually refers to any functions within the 
"kernel/signal.c" file that span line 734, i.e, it equals to 
kernel.function("send_signal"). So it seems to me the only way to put 
probe on a specific line is to use kernel.statements(0x....). But this 
is really troublesome and inconvenient for me. Sometimes I need to 
visit some local variables and their valid location range is beyond 
the function prologue, so using kernel.function(..@lineno) will 
complain not finding that variable.

  So I think it is really helpful if 
kernel.function("*@kernel/signal.c:734") could act as I expected 
before, that is, it will put a probe on line 734 of signal.c. Or else 
SystemTap is of little help to probe somewhere inside a function and 
visit some of its local variables, and I think these are important for 
problem diagnosis.

- Guanglei