What is the difference between /proc/self/stack and output from pstack?

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http://unix.stackexchange.com – I have been looking through the documentation for /proc and the "stack" object being a new'ish object in proc, I have also looked through the kernel commit to create it -- however the documentation does not detail exactly what is in the /proc/self/stack file -- and since I intuitively expected it to be the actual stack of the process -- however the old pstack tool gives a different (and more believable) output. So as an example of the stack for bash $ cat /proc/self/stack [<ffffffff8106f955>] do_wait+0x1c5/0x250 [<ffffffff8106fa83>] sys_wait4+0xa3/0x100 [<ffffffff81013172> (HowTos)