NAME

       warning::buildid - build-id verification failures

DESCRIPTION

       Because  systemtap's  script  translation  / execution stages may be executed at different
       times and places, it is sometimes  necessary  to  verify  certain  invariants.   One  such
       invariant is that if a script was informed by translate-time analysis of executables, then
       those same executables need to be used at run time.  This checking is done based upon  the
       build-id,   a   binary  hash  that  modern  (post-2007)  compilers/toolchains  add  as  an
       NT_GNU_BUILD_ID ELF note to object files and executables.  Use the readelf -n  command  to
       examine the build-ids of binaries, if you are interested.

       Only  scripts  are  sensitive to executables' build-ids: generally those that perform deep
       analysis of the binaries or their debuginfo.  For example, scripts that place .function or
       .statement  probes,  or  use  stack  backtrace-related  tapset functions may be sensitive.
       Other scripts that rely only  on  process.mark  or  kernel.trace  probes  do  not  require
       debuginfo.  See the DWARF DEBUGINFO section in the stapprobes(3stap) man page.

       During  translation,  systemtap  saves  a copy of the relevant files' build-ids within the
       compiled modules.  At run-time, the modules compare the saved ones to the actual  run-time
       build-ids in memory.  The warning message indicates that they did not match, so the module
       will decline placing a probe  that  was  computed  based  upon  obsolete  data.   This  is
       important  for  safety,  as  placing  them  at  an  inappropriate  address could crash the
       programs.  However, this is not necessarily a fatal error, since probes unrelated  to  the
       mismatching binaries may operate.

       A  build-id mismatch could be caused by a few different situations.  The main one is where
       the executable versions or architecture were different between the  systemtap  translation
       and  execution  times/places.   For  example,  one  may  run  a  stap-server on a slightly
       different version of the OS distribution.  Someone may have rebuilt a  new  kernel  image,
       but  preserved the previous version numbers.  The kernel running on the workstation may be
       slightly different from the version being targeted -  perhaps  due  to  a  pending  kernel
       upgrade leaving different files on disk versus running in memory.  If your OS distribution
       uses separate debuginfo packages, the split .debug files may not exactly  match  the  main
       binaries.

       To  disable  build-id verification warnings, if one is confident that they are an artefact
       of build accidents rather than a real mismatch, one might try  the  -DSTP_NO_BUILDID_CHECK
       option.

SEE ALSO

       http://fedoraproject.org/wiki/Releases/FeatureBuildId,
       stap(1),
       stapprobes(3stap),
       warning::debuginfo(7stap),
       error::reporting(7stap)

                                                                          WARNING::BUILDID(7stap)