Re: Problem with vfs probe on Proxmox kernel

[David Smith <dsmith at redhat dot com>]

On 01/25/2017 04:44 PM, Adam Guderski wrote:
> Hello,
> 
> I've got problem running sample traceio.stp script (obtained from
> https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/SystemTap_Beginners_Guide/#traceio2)
> on Proxmox VE 4.4 system. Proxmox is a Debian-based Linux distro which
> uses a custom Ubuntu-based kernel. The Proxmox repository does not
> provide a kernel with debug symbols, so I had to compile it from
> provided sources - version 4.4.35-2-pve, to be specific. Debian repos
> (jessie) provide systemtap in version 2.9, which from what I read does
> not support 4.4 kernels, so I compiled systemtap from sources (from
> master branch, version 3.1/0.159).
> 
> With such setup, I'm able to run sample "hello world" stap script and
> couple of others, but all scripts with vfs probes fail. I attach full
> verbose (-vvv) output here: http://pastebin.com/DiWMsrtr, but I think
> the main error can be explained below. What can I do about it? I
> searched for couple of hours but did not find anything that would help.

As the following states:

> # stap -v traceio2.stp 0xfb00
> Pass 1: parsed user script and 119 library scripts using
> 71608virt/43716res/4464shr/39904data kb, in 140usr/0sys/132real ms.
> semantic error: while resolving probe point: identifier 'kernel' at
> /usr/local/share/systemtap/tapset/linux/vfs.stp:987:19
>         source: probe vfs.write = kernel.function("vfs_write")
>                                   ^
> 
> semantic error: missing x86_64 kernel/module debuginfo [man
> warning::debuginfo] under '/lib/modules/4.4.35-2-pve/build'

Note that a systemtap "hello world" program doesn't need kernel
debuginfo, but a script using vfs probes does need kernel debuginfo.
Does any script that needs debuginfo work, or is it just vfs probes? To
test, try 'stap -l 'kernel.function("*_write")'. You should see items
like 'sys_write' and 'vfs_write' in the output.

systemtap is expecting to find the kernel's debuginfo at
/lib/modules/4.4.35-2-pve/build. Is it there? If not, you'll either need
to move it there or use the 'SYSTEMTAP_DEBUGINFO_PATH' environment
variable to tell systemtap where you've put the debuginfo.

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)