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A Few more corrections on the Systemtap vs Dtrace chart.
- From: "James Dickens" <jamesd dot wi at gmail dot com>
- To: SystemTAP <systemtap at sources dot redhat dot com>
- Date: Thu, 14 Sep 2006 08:25:59 -0500
- Subject: A Few more corrections on the Systemtap vs Dtrace chart.
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I will assume that you haven't had a chance to update the chart with
my corrections, I submitted earlier. By the way do you really think
that Sun Engineers did the BSD and OSX ports of DTrace, you could fix
the chart since it already was changed to reflect BSD support.
I do have a few more corrections.
[b]probe arbitrary points in code (function entry, exit, interior) [/b]
In the kernel, DTrace can probe all function entry and exit points, so
you can probe any point where a function is called, including both
entry and exit of any function.
As I documented earlier you can probe any assembly instruction in
userland tasks.
[b]Extract arbitrary data at probe point[/b]
Systemtap is limited to accessing variables when the program has debug
data intact.
DTrace can access any variable that is passed into a function or
returned from a function.
This leaves the user, left to figure out the value in a variable after
built-in operations have occurred, mostly math and storage of values
in to a variable both of which should be easy to compute. And
following flow control statements.
DTrace also has access to userland registers (with uregs) including
segment registers necessary to read data from the callstack and heap.
Should following the functions logic be too difficult.
All of this is possible in DTrace whether or not you have debug
information in tact.
Solaris also has a kernel debugger should you wish to access any point
in the kernel and userland and single step or access and change any
place in memory, or do any other destructive action your heart
desires.
You could also include a link to the Dtrace guide should visitors to
the chart need further details on its implementation.
http://docs.sun.com/app/docs/doc/817-6223
some may also enjoy reading
http://learningsolaris.com/docs/dtrace_tips_public.pdf
its the advanced dtrace guide that covers things that haven't yet made
it into the official documentation along with things that DTrace can't
do that you may decide to add to your chart and may give you ideas on
how to better use and enhance Systemtap.
James Dickens
uadmin.blogspot.com