Sigh. No, I missed one thing. If application use
makecontext()/swapcontext() pair,
ESP is not reliable way to detect pthread stack. At that time the
stack is still marked
as anonymous memory.
This is not wrong, because it essentially gives the correct picture of
the state of that task -- the task is using another vma as a stack
during that point and not the one it was allotted by pthreads during
thread creation.
I don't think we can successfully stick to the idea of trying to mark
stack space allocated by pthreads but not used by any task *currently*
as stack as long as the allocation happens outside the kernel space.
The only way to mark this is either by marking the stack as
VM_GROWSDOWN (which will make the stack grow and break some pthreads
functions) or create a new flag, which a simple display such as this
does not deserve. So it's best that this sticks to what the kernel
*knows* is being used as stack.