Re: Calling kernel functions from kprobes/jprobes

[fche@redhat.com (Frank Ch. Eigler)]

"Samuel" <samuelkorpi@myway.com> writes:

> [...]  I am using kprobes/jprobes to try and understand how IP
> options are handled in the kernel. From one of these probes I want
> to call another function inside the kernel, namely
> ip_options_get_from_user. [...]

Other than symbol exporting issues, you may encounter another problem
that we have encountered in systemtap (which is also a kprobes
client).  That is that the context where the kprobe was placed may be
such that calling most ordinary kernel routines is unsafe.  In
particular, ip_options_get_from_user may sleep, which may or may not
be legal from the context of the kprobe.  (In systemtap probes, we
don't permit anything to block/sleep/schedule, so instead suffer
absent-page errors.)

- FChE