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Re: user mode backtrace
- From: fche at redhat dot com (Frank Ch. Eigler)
- To: david_list at boreham dot org
- Cc: SystemTap <systemtap at sources dot redhat dot com>
- Date: 19 Oct 2006 19:49:53 -0400
- Subject: Re: user mode backtrace
- References: <4537E44C.6040604@boreham.org>
David Boreham <david_list@boreham.org> writes:
> I'd like to get a stack trace for the process that made the system
> call I'm probing [...]
Yes, that's an understandable need.
> But I'm worried that [calling gdb] might deadlock since the process
> is inside a system call.
Indeed, that would be several orders of magnitude too slow and invasive.
We don't yet have a good answer to user-space stuff in general. We
may adopt a mixture of two approaches: one where the compiled
systemtap probes get some extract of backtrace-enabling unwind
information for selected user-space programs and libraries (so the
backtrace processing can be done instantly right there); and another
one where the probe may snapshot only an approximation (say a vector
of probable PCs from the thread's stack frame), and rely on a
user-space helper to correct/complete it for output later, off-line.
- FChE