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error::sdt(7stap) [centos man page]

ERROR::SDT(7stap)														 ERROR::SDT(7stap)

error::sdt - <sys/sdt.h> marker failures DESCRIPTION
Systemtap's <sys/sdt.h> probes are modeled after the dtrace USDT API, but are implemented differently. They leave a only a NOP instruction in the userspace program's text segment, and add an ELF note to the binary with metadata. This metadata describes the marker's name and parameters. This encoding is designed to be parseable by multiple tools (not just systemtap: GDB, the GNU Debugger, also contains sup- port). These allow the tools to find parameters and their types, wherever they happen to reside, even without DWARF debuginfo. The reason finding parameters is tricky is because the STAP_PROBE / DTRACE_PROBE markers store an assembly language expression for each op- erand, as a result of use of gcc inline-assembly directives. The compiler is given a broad gcc operand constraint string ("nor") for the operands, which usually works well. Usually, it does not force the compiler to load the parameters into or out of registers, which would slow down an instrumented program. However, some instrumentation sites with some parameters do not work well with the default "nor" con- straint. unresolveable at run-time GCC may emit strings that an assembler could resolve (from the context of compiling the original program), but a run-time tool can- not. For example, the operand string might refer to a label of a local symbol that is not emitted into the ELF object file at all, which leaves no trace for the run-time. Reference to such parameters from within systemtap can result in "SDT asm not understood" errors. too complicated expression GCC might synthesize very complicated assembly addressing modes from complex C data types / pointer expressions. systemtap or gdb may not be able to parse some valid but complicated expressions. Reference to such parameters from within systemtap can result in "SDT asm not understood" errors. overly restrictive constraint GCC might not be able to even compile the original program with the default "nor" constraint due to shortage of registers or other reasons. A compile-time gcc error such as "asm operand has impossible constraints" may result. There are two general workarounds to this family of problems. change the constraints While compiling the original instrumented program, set the STAP_SDT_ARG_CONSTRAINT macro to different constraint strings. See the GCC manual about various options. For example, on many machine architectures, "r" forces operands into registers, and "g" leaves operands essentially unconstrained. revert to debuginfo As long as the instrumented program compiles, it may be fine simply to keep using <sys/sdt.h> but eschew extraction of a few indi- vidual parameters. In the worst case, disable <sys/sdt.h> macros entirely to eschew the compiled-in instrumentation. If DWARF debuginfo was generated and preserved, a systemtap script could refer to the underlying source context variables instead of the positional STAP_PROBE parameters. SEE ALSO
stap(1), stapprobes(3stap), error::dwarf(7stap),,, error::reporting(7stap) ERROR::SDT(7stap)

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ERROR::PASS5(7stap)													       ERROR::PASS5(7stap)

error::pass5 - systemtap pass-5 errors DESCRIPTION
Errors that occur during pass 5 (execution) can have a variety of causes. exceptional events during script execution The systemtap translator and runtime include numerous error checks that aim to protect the systems and the users from mistakes or transient conditions. The script may deliberately call the error() tapset function to signal a problem. Some memory needed for accessing $context variables may be temporarily unavailable. Consider using the try/catch construct to wrap script fragments in exception-handling code. Consider using the stap --suppress-handler-errors or stap --skip-badvars option. resource exhaustion One of several types of space or time resource limits may be exceeded by the script, including system overload, too many tuples to be stored in an array, etc. Some of the error messages identify the constraint by macro name, which may be individually raised. Consider using the stap --suppress-handler-errors option. Extend or disable resource limits using the stap -DLIMIT=NNNN option. remote execution server problems If you use the stap --remote option to direct a systemtap script to be executed somewhere else, ensure that an SSH connection may be made to the remote host, and that it has the current systemtap runtime installed & available. installation/permission problems It is possible that your installation of systemtap was not correctly installed. For example, the /usr/bin/staprun program may lack the necessary setuid permissions, or your invoking userid might not have sufficient privileges (root, or stapusr and related group memberships). Environment variables may interfere with locating /usr/libexec/.../stapio. errors from target program The program invoked by the stap -c CMD option may exit with a non-zero code. uncaught exceptions in the target program When using --runtime=dyninst you may encounter an issue where the target program aborts with a message like "terminate called after throwing an instance of 'foo_exception'". This is unfortunately a limitation of Dyninst, which sometimes prevents exceptions from properly unwinding through instrumented code. GATHERING MORE INFORMATION
Increasing the verbosity of pass-5 with an option such as --vp 00001 can help pinpoint the problem. SEE ALSO
stap(1),, error::fault(7stap), error::reporting(7stap) ERROR::PASS5(7stap)
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