Jonathan, thanks for taking an objective look at the tracing tools and giving your informed opinion. I would like to give few clarifications mainly from SystemTap point of view.
On the documentation SystemTap does provide a manual pages that explains the probe points available in the tapsets so one doesn't have to read the source code. I agree we can improve the documentation and we are addressing this issue and you will see detailed language reference manual soon on the website.
SystemTap language does support static markers. The static marker infrastructure in the kernel is currently undergoing review in LKML and we are expecting that to make to mainline soon. Once it makes to mainline SystemTap will exploit that.
We designed SystemTap to be flexible yet safe to make it usable to wide variety of audience. SystemTap also provides predefined probe points that are safe to probe. An administrator can limit to only these probe points without worrying about safety. SystemTap also provides ability for a developer or support person to place probes anywhere using advanced guru mode hence the warnings of safety. I agree with you that bundled tapsets contain limited probe points and needs enhancement and work is in progress.
Safety is one of the most important considerations in all of our design decisions. The generated code also has safety checks very similar to what a virtual machine provides.
I agree with you that SystemTap provides feature rich language including ability to print stack trace using backtrace() construct.
SystemTap project is very young (2.5 years) and it is still work in progress. We have come a long way in this short amount of time due to our flexible architecture but I agree with you that we need to focus making it usable to administrators of all levels.
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