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1) I have installed SystemTap but am getting a "semantic error: libdwfl
failure (missing kernel debuginfo): No such file or directory", when I
try to run a script. What am I missing? How do I fix it?
This error message is related to the processing of debug-information. It
may simply be missing, or may have some consistency/correctness problems.
So please make sure that kernel-debuginfo rpm is installed in your system
or in case of custom built kernels, your kernel is compiled with debug
options(ref Q.2). Please refer this link
http://sources.redhat.com/systemtap/tutorial/node27.html
Common error messages that one may encounter while using SystemTap along
with possible reasons for them, are listed at
http://sources.redhat.com/systemtap/tutorial/node23.html and
http://sources.redhat.com/systemtap/tutorial/node27.html
2) What config options need to be enabled to be able to use SystemTap on
custom built kernels?
Look at http://sources.redhat.com/systemtap/wiki/SystemTapWithSelfBuiltKernel
for the specific config options to be enabled for SystemTap.
3) I have a kernel built with options listed in (2), but still can't get
SystemTap to work. What am I missing?
See Q2. Also, if you've used 'make install' to install your custom built kernel,
it may not have copied the uncompressed 'vmlinux' to /boot/vmlinux-'uname-r'
4) Is it possible for me to view the kernel module generated by SystemTap?
You can specify -p3 to look at the kernel module code translated by SystemTap.
stap -p3 <script> | less
stap -p3 -e '...' | less
man stap(1)
[...]
-p NUM stop after pass NUM 1-5, instead of 5
(parse, elaborate, translate, compile, run)
5) How do I run prebuilt SystemTap modules?
Prebuilt SystemTap modules can be run using the 'staprun(8)'
$ staprun /path/to/<name>.ko
Also see
http://sources.redhat.com/git/gitweb.cgi?p=systemtap.git;a=blob_plain;f=README.security;hb=HEAD
6) What should I do when some tapsets functions fails to resolve like
"semantic error: unresolved arity-1 function: identifier 'log'"
Ensure that the tapsets are installed at the right location:
/usr/share/systemtap/tapset/ (in RHEL or Fedora) or
/usr/local/systemtap/tapset if you install from source.
7) This is way cool! I want to write my own scripts. Where do I look for more
information?
a. Read the SystemTap tutorial - http://sources.redhat.com/systemtap/tutorial/
b. Read the Language reference guide at - http://sourceware.org/systemtap/langref/
c. Check out our wiki - http://sources.redhat.com/systemtap/wiki/
d. Look at http://sources.redhat.com/systemtap/getinvolved.html as to how you
can get involved.
e. Subscribe to our mailing list at http://sources.redhat.com/ml/systemtap/.
f. Join our IRC channel on freenode (#systemtap) and fire away your queries.
8) Is it possible to override some of the macros in SystemTap generated
"C" module.
Yup. Use -D option with stap command.
man stap
[...]
-D NM=VAL emit macro definition into generated C code
9) What is a tapset?
A tapset is just a script that designed for reuse by installation into a
special directory.See http://sources.redhat.com/systemtap/tutorial/node15.html
for more information.
10) I see that there is no tapset for my favourite subsystem. What do I do?
SystemTap community encourages users to write tapsets. See our tapset developer
guide at http://sources.redhat.com/git/gitweb.cgi?p=systemtap.git;a=blob_plain;f=tapset/DEVGUIDE;hb=HEAD
Learn how to write your own tapset looking at the existing ones under
/usr/share/systemtap/tapset.
11) I hear the latest Linux Kernels come with marker support. Does SystemTap
support markers?
Yes, SystemTap supports kernel markers. See
http://sources.redhat.com/systemtap/wiki/UsingMarkers for more information.
12) I am a non-root user, but still want to run SystemTap scripts.
Is that possible?
Yes, it is possible. Add yourself as a member of 'stapusr' group. Members
of stapusr group can run SystemTap scripts/modules located at
/lib/modules/`uname -r`/systemtap directory.
13) This is fantastic! But how does it all work?
Internals of translation in SystemTap is described in src/INTERNALS* file.
Documentation on kprobes is available at kernel source
(Documentation/kprobes.txt).
* http://sources.redhat.com/git/gitweb.cgi?p=systemtap.git;a=blob_plain;f=INTERNALS;hb=HEAD
14) Do I have to be a RedHat Enterprise Linux/Fedora user to be able to
use SystemTap?
No, It is possible to use SystemTap on other Linux distributions. Our
wiki http://sources.redhat.com/systemtap/wiki has more information on this.
15) I found a bug when using the tool. How do I report it?
a. You can file a bug at SystemTap bugzilla
http://sources.redhat.com/bugzilla/enter_bug.cgi?product=systemtap
b. Drop us a note with details of the bug at systemtap@sources.redhat.com
16) I'd like to contribute to the project. Where to I start?
See http://sources.redhat.com/systemtap/getinvolved.html. You can even work on
some bugs listed in SystemTap bugzilla (look for "current bugs/pending features"
link at the bottom of the getinvolved page)
17) I am a RHEL/Fedora user, but don't have the debuginfo rpm. Where can I find it?
For RHEL, you can find the rpm at: http://people.redhat.com/duffy/debuginfo.
For Fedora, you can run: yum --enablerepo=fedora-debuginfo install
kernel-debuginfo
18) How can I find a list of blacklisted functions?
See output of:
stap -vvv -e 'probe kernel.function("*") {}' -p4 2>&1 | grep blacklisted
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