IZ56256: FIRSTPRIVATE OPENMP CLAUSE CAUSES CRASH

September 2012 PTF for XL Fortran for AIX, V12.1
October 2010 PTF for XL Fortran for AIX, V12.1
November 2009 PTF for XL Fortran for AIX, V12.1
March 2010 PTF for XL Fortran for AIX, V12.1
April 2010 PTF for XL Fortran for AIX, V12.1
June 2010 PTF for XL Fortran for AIX, V12.1
February 2011 PTF for XL Fortran for AIX, V12.1
May 2011 PTF for XL Fortran for AIX, V12.1
July 2011 PTF for XL Fortran for AIX, V12.1
October 2011 PTF for XL Fortran for AIX, V12.1
February 2012 PTF for XL Fortran for AIX, V12.1
January 2013 PTF for XL Fortran for AIX, V12.1
XL Fortran for AIX Fix Pack 18 (July 2013) for 12.1
XL Fortran for AIX Fix Pack 19 (October 2013) for 12.1
XL Fortran for AIX Fix Pack 20 (October 2014 PTF) for 12.1

APAR status

• Closed as program error.

Error description

• When using the 'firstprivate' OpenMP clause in the following
  testcase, the executable would segfault at runtime.
  
  Compile line:
  xlf_r SBP_omp_firstprivate.f90 -O3 -q64 -qsmp=omp
  -bmaxstack:0x1000000000
  
  ===== TESTCASE:
  $cat SBP_omp_firstprivate.f90
  program SBP_mono_omp
  
    implicit none
  
  !!! Attention !!! : OpenMP - Memoire necessaire : 3600 Mo + 3600
  Mo par thread
  !!! Attention !!! : Mono - Memoire necessaire : 5 Go
    integer(kind=8), parameter :: puissance = 27, n = 2**puissance
    integer(kind=8) :: i, pas, rep=200, nb_iterations
  
    print *,'\n *** IDRIS SBP ***'
    nb_iterations=n*rep
    call SBP
  
  contains
  
    subroutine SBP
      real(kind=kind(1.d0)), dimension(3*n) :: TAB
      real(kind=kind(1.d0)) :: t1, t2, tps_elapsed, tps_cpu
      real(kind=kind(1.d0)) :: debit
      integer :: nbp_max, freq_p, nbp_final_local
      integer :: nbp_init, nbp_final, numth, nbth
      !$ integer :: OMP_GET_THREAD_NUM, OMP_GET_NUM_THREADS
  
      TAB(1:n) = 1.013
      TAB(n+1:2*n) = 1.0014
      TAB(2*n+1:3*n) = 0.000012
  
      nbth=1
      !$OMP PARALLEL
       !$ nbth  = OMP_GET_NUM_THREADS()
      !$OMP END PARALLEL
  
      call system_clock(count_rate=freq_p, count_max=nbp_max)
  
      call cpu_time(t1)
      call system_clock(nbp_init)
      !Note: if you change firstprivate to private it works fine.
      !$OMP PARALLEL firstprivate(TAB)
      call CALCUL(TAB(1:n),TAB(1+n:2*n),TAB(2*n+1:3*n))
      !$OMP END PARALLEL
      call system_clock(nbp_final)
      call cpu_time(t2)
  
      if (nbp_final>nbp_init) then
         tps_elapsed=real(nbp_final-nbp_init)/real(freq_p)
      else
         tps_elapsed=real(nbp_final-nbp_init+nbp_max)/real(freq_p)
      endif
      tps_cpu=(t2-t1)/nbth
      debit = nb_iterations*4*8/(1000000*tps_elapsed)
  
      print *,'\n Resultat sur ',nbth,' threads'
  print '(" Tps elapsed, Tps CPU moy/thread, debit moy/thread = ",
  f9.2, f9.2, f9.3)' &
              ,tps_elapsed,tps_cpu,debit
    end subroutine SBP
  
    subroutine CALCUL(A,B,C)
      real(kind=kind(1.d0)), dimension(:), intent(in) :: B, C
      real(kind=kind(1.d0)), dimension(:), intent(inout) :: A
      integer(kind=8) :: i,j
  
      do j=1,rep
         do i = 1,n
            A(i)=A(i)*B(i)+C(i)
         enddo
      enddo
  
    end subroutine CALCUL
  
  end program SBP_mono_omp
  
  
  
  =====ACTUAL OUTPUT:
  $ ./a.out
  
   *** IDRIS SBP ***
  Segmentation fault(coredump)
  &
  
  
  =====EXPECTED OUTPUTS:
  $ ./a.out
  
   *** IDRIS SBP ***
  
   Resultat sur  1  threads
   Tps elapsed, Tps CPU moy/thread, debit moy/thread =     93.29
  67.95 9207.776
  $
  

Local fix

• n/a
  

Problem summary

• This problem was exposed when using the firstprivate OpenMP
  directive with -q64.
  
  There was an issue with the compiler optimizer where the length
  for memcpy was
  incorrectly generated as a sign extended 32 bit word in 64 bit
  mode.
  

Problem conclusion

• The compiler optimizer has been fixed to generate the correct
  sign extended word in 64 bit mode.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  LI75012 LI75020

Fix information

• Fixed component name

  XL FORTRAN AIX

• Fixed component ID

  5724U8200

Applicable component levels