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Re: Systemtap FAQ
- From: William Cohen <wcohen at redhat dot com>
- To: joaoandreferro at sapo dot pt, systemtap at sourceware dot org
- Date: Mon, 25 Aug 2014 10:19:51 -0400
- Subject: Re: Systemtap FAQ
- Authentication-results: sourceware.org; auth=none
- References: <20140822215107 dot Horde dot josCQqoI7qv_J-TSWsbdWA4 at mail dot sapo dot pt>
On 08/22/2014 04:51 PM, joaoandreferro@sapo.pt wrote:
> Hello all,
>
> I've just installed Systemtap, and to start I have a couple of doubts that I
> would like to share with you:
>
> 1 - Firstly, what I'm trying to achieve is some kind of interrupt handler:
> I would like to momentarily interrupt the execution of the OS, and then be
> able to run some code of mine (to start, inject a single bit-flip into a
> CPU register), and then resume the execution of the OS, with the
> possibility of having information on the pre-interruption context. Is this
> somehow possible with Systemtap?
Hi,
It sound like you are trying to do fault injection with systemtap. SystemTap has been used successfully for fault injection on the Linux kernel's scsi layer:
http://lwn.net/Articles/289932/
SystemTap's guru mode (-g) has the ability to modify target variable value. For the kprobes, uprobe, and timer based probes you probably could change the values in the pt_regs struct and effect a bit-flip.
You could use the associative arrays in systemtap to store information about where (backtrace) and when these bit-flips are done. Look at the the tapset library for information on various functions to get timeofday and backtraces https://sourceware.org/systemtap/tapsets/ .
>
> 2 - I'm using CentOs 6.5 32 bit (kernel version 2.6.32-431.23.3.el6.i686).
> Will Systemtap work here? I think this information may be relevant, since
> this isn't the last version of the distro, and some other tools I've
> already tried to use in the past didn't worked because of my (old) kernel
> version.
SystemTap should work on CentOs. SystemTap does need other rpms such as matching kernel-devel and kernel-debuginfo. You might need to manually download and install those because yum typically tries to get the most recent versions of packages. The stap-prep command should list out what packages you need to get sysetmtap working on the system. The following wiki page provides some additional suggestions on setting up systemtap on CentOs:
https://sourceware.org/systemtap/wiki/SystemTapOnCentOS
-Will