error::pass2 - systemtap pass-2 errors
Errors that occur during pass 2 (elaboration) can have a variety of causes.
Common types include:
- missing debuginfo
- The script requires debuginfo to resolve a probe point, but could not find
any. See error::dwarf(7stap) and warning::debuginfo(7stap)
for more details.
- unavailable probe point classes
- Some types of probe points are only available on certain system versions,
architectures, and configurations. For example, user-space
process.* probes may require utrace or uprobes capability in the
kernel for this architecture.
- unavailable probe points
- Some probe points may be individually unavailable even when their class is
fine. For example, kprobe.function("foobar") may fail if
function foobar 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
stap-prep 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: $foo->bar->baz even if in C one would
- unavailable context variables
- Systemtap scripts often wish to refer to variables from the context of the
probed programs using $variable notation. These variables may not
always be available, depending on versions of the compiler,
debugging/optimization flags used, architecture, etc. Use stap -L
PROBEPOINT to list available context variables for given probes. Use
the @defined() expression to test for the resolvability of a
context variable expression. Consider using the stap --skip-badvars
option to silently replace misbehaving context variable expressions with
zero. Experiment with the stap --prologue-searching option.
- module cache inconsistencies
- Occasionally, the systemtap module cache ($HOME/.systemtap/cache) might
contain obsolete information from a prior system configuration/version,
and produce false results as systemtap attempts to reuse it. Retrying with
stap --poison-cache ... forces new information to be generated.
Note: this should not happen and likely represents a systemtap bug.
Please report it.
GATHERING MORE INFORMATION¶
Increasing the verbosity of pass-2 with an option such as --vp 02 can
help pinpoint the problem.