stack trace changes

[Mike Mason]

Thanks for working on this.  See comments below...

Martin Hunt wrote:
> I've checked in a rewrite of the stack trace code.  I rewrote i386 and
> x86_64 only. ppc64 and ia64 should still work as before, unless I made
> any errors while reorganizing the code.

I'll test on ppc64 after the build error is fixed in the ppc64 runtine
(see bug 3051).

> 
> In 2.6.18 there is code to use DWARF to accurately unwind the stacks.
> The new code uses this if available, otherwise it falls back to the
> inaccurate unwinder.  Some situations like kretprobe trampolines confuse
> the unwinder and it does what it can accurately then uses the inaccurate
> unwinder. In all cases, it now says when the trace in not accurate.

I tested print_backtrace on 2.6.17-1.2187_FC5 on x86_64. I now see a 
single line(as before) followed by "Inexact backtrace:" and then 
nothing. Is there no way to get additional stack info on x86_64 
kernels earlier than 2.6.18?  Just want to know what to expect.

I tested on 2.6.18 as well and it appears to work as you described.

Thanks again for your efforts.

- Mike