DESCRIPTIONErrors that occur during pass 2 (elaboration) can have a variety of causes. Common types include:
- unavailable probe point classes
Some types of probe points are only available on certain system versions,
architectures, and configurations. For example, user-space
probes may require utrace or uprobes capability in the kernel for this
- unavailable probe points
Some probe points may be individually unavailable even when their class is
fine. For example,
may fail if function
does not exist in the kernel any more. Debugging or symbol data may be absent for
some types of
.function or .statement
probes; check for availability of debuginfo. Try the
program to download possibly-required debuginfo.
Use a wildcard parameter such as
stap -l 'kprobe.function(*foo*)'
to locate still-existing variants. Use
! or ?
probe point suffixes to denote optional / preferred-alternatives, to let
the working parts of a script continue.
There might be a spelling error in the probe point name ("sycsall" vs.
"syscall"). Wildcard probes may not find a match at all in the
tapsets. Recheck the names using
stap -l PROBEPOINT.
Another common mistake is to use the
operator instead of the correct
when dereferencing context variable subfields or pointers:
even if in C one would say
- unavailable context variables
Systemtap scripts often wish to refer to variables from the context of the
probed programs using
notation. These variables may not always be available, depending on versions
of the compiler, debugging/optimization flags used, architecture, etc. Use
stap -L PROBEPOINT
to list available context variables for given probes. Use the
expression to test for the resolvability of a context variable expression.
Consider using the
option to silently replace misbehaving context variable expressions with zero.
Experiment with the
- module cache inconsistencies
Occasionally, the systemtap module cache ($HOME/.systemtap/cache) might
contain obsolete information from a prior system configuration/version,
and produce false results as systemtap attempts to reuse it. Retrying
stap --poison-cache ...
forces new information to be generated.
this should not happen and likely represents a systemtap bug. Please
GATHERING MORE INFORMATIONIncreasing the verbosity of pass-2 with an option such as --vp 02 can help pinpoint the problem.