return function clarification

[domenico dot dileo at unina dot it]

Hello,
I'm trying to understand a bit more on the
function call sequence.
I'm just considering the memory manager sub-component
and understand the function call graph
at runtime (i.e., when there is a specific process
running).

I wrote the following stap script

probe kernel.function("*@mm/*.c").call{
	print_invocation("MM", 1)
}
probe kernel.function("*@mm/*.c").return{
	print_invocation("MM", -1)
}

function print_invocation(subsystem, indent){
		if(pid()== target()){
		 printf(" %s %s %s %s %p\n",
			subsystem,
			thread_indent(indent),
			(indent>0?"->":"<-"),
			probefunc(), addr())
		}
}

The output (output1) of the script (when "top" command is running) is
[LineNumber Subsystem  thread_indent probefunc PC_address]

1 MM      0 top(14861): -> kmem_cache_alloc 0xffffffffc018c880
2 MM   1701 top(14861):  -> should_failslab 0xffffffffc018bea0
3 MM   1799 top(14861):  <- should_failslab 0xffffffffc018c8a2
4 MM   1839 top(14861):  -> kmem_flagcheck 0xffffffffc018a5f0
5 MM   1853 top(14861):  <- kmem_flagcheck 0xffffffffc018c8bb

Now if I use the addr2line utility with the PC addresses
on the last column, I get output2

1 MM  ->  kmem_cache_alloc  /mm/slab.c:3823
2 MM   ->  should_failslab  /mm/slab.c:3335
3 MM   <-  __cache_alloc  /mm/slab.c:3667
4 MM   ->  kmem_flagcheck  /mm/slab.c:2882
5 MM   <-  __cache_alloc  /mm/slab.c:3671

I have 2 questions:
1) How should I interpret the call sequence in output1?
I suppose the meaning is Kmem_cache_alloc calls should_fail_slab
which returns (line 3) and then kmem_cache_alloc calls kmem_check
which executes and returns and  so on... right?

2) In output2 the name of the function at line 3, 5 and in general
every time the function returns is different from output1.
To obtained those names I just used addr2line with the PC_address
in output1.
For instance, for the 3rd line of output2 I use
addr2line -f -e /boot... c018c8a2 which returns  __cache_alloc

I'm running systemtap 1.6 on Gentoo, kernel 2.6.24
Thank you in advance for any help.



Domenico Di Leo, PhD student, Universit? degli Studi di Napoli Federico II
Ph:     +39 081 676770
Fax:    +39 081 676574
Web: http://wpage.unina.it/domenico.dileo