﻿ Dave Pacheco's Blog. Systems software engineering
Understanding DTrace ustack helpers  or, everything you ever
wanted to know about stack traces  I promised this post over a
year ago, and now that someone’s actually working on a new
ustack helper, I thought it was finally time to write about what
ustack helpers are, how they work, and how I went about building
one for Node.js. Only a handful of ustack helpers have ever been
written: Node, Java, Python, and PHP (the last of which is
believed lost to the sands of time), so this post is mainly for
a narrow audience of developers, plus anyone who’s interested in
how this all works.  This post covers a lot of the background
you need to understand the details. For more information, check
out my ACM article on Postmortem Debugging in Dynamic
Environments. Though this post covers dynamic tracing, the
challenges are similar to those for postmortem debugging, since
both involve operating on a snapshot of program state without
the aid of the VM itself.  The value of