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Re: print_backtrace not printing full stack


On Thu, 2006-08-10 at 13:45, Frank Ch. Eigler wrote:
> We also
> know that kretprobes did or does have problems with corrupting
> backtraces for even plain nested kernel-side probes.

Still does.  You'll see "kretprobe_trampoline" in the stack trace
wherever kretprobes has hijacked the return address of a kretprobed
function.  (The stack trace is not otherwise corrupted, to my
knowledge.)

It is theoretically possible, though a bit messy, for kprobes to dig out
the real return address corresponding to the Nth appearance of
kretprobe_trampoline in your stack trace.  Since SystemTap has its own
implementation of backtrace(), it could be made to do that.  But then
we'd run up against the Catch-22 of
a) There's no in-kernel use of this kretprobes feature ("and by the way,
SystemTap is $#%&!").
b) Don't $#%&! up the in-kernel stack-trace implementations with this
$#%&!.  Fix kretprobes!

Jim


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