Re: print_backtrace not printing full stack

[Jim Keniston <jkenisto at us dot ibm dot com>]

On Thu, 2006-08-10 at 14:35, Mike Mason wrote:
> Hmm... I didn't think about the user portion of the stack being missing.
> Perhaps open() isn't a good example.  I tried probing the entry to open()
> and printing the backtrace.  Saw the same results.

You're probing sys_open(), which is dispatched directly from the system
call table, at least on some architectures.  On i386, I'd expect to see
an entry for sys_open and one for the code that called sys_open
(sysenter_past_esp in entry.S), but that's all.  sysenter_past_esp is a
label in what is essentially the entry point into the kernel for system
calls.

Which architecture are you testing?

> Then I tried a few
> other probe points, including schedule() in sched.c.
> No matter where I
> probe, I only get one line of the stack.

That sounds like a bug.  Is that one line in the probed function, in its
caller, or what?  (I'm assuming you don't see the kretprobe_trampoline
line if it's not a kretprobe.)

BTW, on powerpc, at least, print_backtrace() reports the bulk of the
stack trace as one long line, apparently no matter how many functions
are reported.  Are you seeing just one function reported, or multiple
functions on one line?

> 
> Mike

Jim