trusty (7) error::pass2.7stap.gz
NAME
error::pass2 - systemtap pass-2 errors
DESCRIPTION
Errors 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 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. 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.
typos 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 say foo->bar.baz.
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.
GATHERING MORE INFORMATION
Increasing the verbosity of pass-2 with an option such as --vp 02 can help pinpoint the problem.
SEE ALSO
stap(1), stapprobes(3stap), probe::*(3stap), error::dwarf(7stap), error::inode-uprobes(7stap), warning::debuginfo(7stap), error::reporting(7stap) ERROR::PASS2(7stap)