LI73256: XLF_R CORE DUMPS WITH RANDOM_NUMBER() AND -Q64

July 2008 Update for XL Fortran Advanced Edition for Linux, V11.1
February 2010 Update for XL Fortran Advanced Edition for Linux, V11.1
June 2009 Update for XL Fortran Advanced Edition for Linux, V11.1
February 2011 Update for XL Fortran Advanced Edition for Linux, V11.1
March 2008 Update for XL Fortran Advanced Edition for Linux, V11.1
November 2008 Update for XL Fortran Advanced Edition for Linux, V11.1

APAR status

• Closed as program error.

Error description

• Following test case core dumps with random_number() compiled
  with *_r and -q64
  
  $xlf_r foo.f -q64
        program foo
        implicit none
        real*8, allocatable, dimension(:,:) :: a
        integer, parameter :: n = 50000
        integer :: istat
  
        allocate(a(n,n),stat=istat)
        if (istat.ne.0) stop 1
        call random_number(a)
        print *, a(1,1)
        deallocate(a)
        end
  
  $./a.out
  Memory fault(coredump)
  
  if n<45000, the problem will go away.
  

Local fix

• n/a
  

Problem summary

• When invocations with the _r suffix are used to link, the
  run-time treats the resulting executable as threaded.
  
  With threaded applications, the random_number() intrisic
  partitions the array and creates "processors online*2"
  number of threads to perform the function in parallel.
  
  The problem is a variable used to keep the number of
  elements for each thread is defined as a 32-bit type
  and it overflows when the array is very large.
  
  Users who call random_number() with a very large
  array (in case of this APAR, 2.5G elements) and use
  the *_r invocation to link or have -lpthreads on the link
  command line are affected.  This defect affects 64-bit
  applications only.
  

Problem conclusion

• Compiler has changed the type of the offending variable from
  32-bit to 64-bit.
  

Temporary fix

Comments

APAR Information

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

  IZ10203

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

Fix information

• Fixed component name

  XL FORTRAN RHEL

• Fixed component ID

  5724S7410

Applicable component levels

• RB10 PSN IZ10203

     UP06/09/13