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

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

NAME

       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),
       http://gcc.gnu.org/onlinedocs/gcc/Constraints.html,
       http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation,
       error::reporting(7stap)

																 ERROR::SDT(7stap)

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

NAME

       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),
       http://sourceware.org/systemtap/wiki/TipExhaustedResourceErrors,
       error::fault(7stap),
       error::reporting(7stap)

															       ERROR::PASS5(7stap)

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

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