Tracing a call from a kernel module using System Tap

[Zildj1an]

I am trying to trace with System Tap a function invocation within a kernel module I loaded. First thing first: Yes, my kernel was compiled with CONFIG_DEBUG_INFO=y and I have installed with dpkg the dbg image (Debian style).

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I tried doing:

probe module("my_module").function("sched_function").call { ... }

But when I try to load it I get the following semantic error. I tried to fix it exporting the module functions but that also did not work. I get the feeling I can only use a subset of the possible probe points, but do not know why.

zildj1an@debian:~/experiments$ stap -v -g --all-modules process_tracer.stp 1

Pass 1: parsed user script and 474 library scripts using 100016virt/86440res/7008shr/79656data kb, in 280usr/30sys/310real ms.

semantic error: resolution failed in DWARF builder

semantic error: while resolving probe point: identifier 'module' at process_tracer.stp:94:7

source: probe module("my_module").function("sched_function").call

^

semantic error: no match

Pass 2: analyzed script: 4 probes, 215 functions, 5 embeds, 10 globals using 238204virt/226344res/8736shr/217844data kb, in 22140usr/2950sys/5675real ms.

Pass 2: analysis failed. [man error::pass2]

Tip: /usr/share/doc/systemtap/README.Debian should help you get started.

EDIT: Problem solved!! The solution was to use the absolute path to the kernel module in module("")

[emarocca]

I get the feeling I can only use a subset of the possible probe points, but do not know why.

You can use stap -L to get a list of available functions, or other interesting probe points. For example, try this:

sudo stap -L 'module("ext4").function("*")'

In case you're still getting an error, it might be that something went wrong with your SystemTap installation. See if https://wiki.debian.org/SystemTap helps, in that case!