IV31754: XLCENTRY ABEND WITH ATOMIC KEYWORD

November 2012 PTF for XL C for AIX, V12.1
November 2012 PTF for XL C/C++ for AIX, V12.1
March 2013 PTF for XL C for AIX, V12.1
March 2013 PTF for XL C/C++ for AIX, V12.1

APAR status

• Closed as program error.

Error description

• The test case makes use of the OpenMP "atomic" clause
  incorrectly but instead of giving an error message, the compiler
  abends and produces a Signal 11.
  
  
  ===== COMPILE COMMAND:
  mpixlc_r -g -O3 -qstrict -qtm -qsmp=omp:speculative -c
  atomic_bug.c
  
  
  ===== TESTCASE:
  $ cat atomic_bug.c
  #include <stdio.h>
  
  #define SIZE 400
  
  int main(void)
  {
      int v, w, z;
      int a[SIZE], b[SIZE];
  
      for (v=0; v<SIZE; v++)
      {
          a[v] = v;
          b[v] = -v;
      }
  
      #pragma omp parallel for private(v,w,z)
      for (v=0; v<SIZE; v++)
        for (w=0; w<SIZE; w++)
          for (z=0; z<SIZE; z++)
          {
            #pragma omp atomic
            {
              a[v] = a[w] + b[z];
            }
          }
  
      printf("done \n");
  
      return 0;
  }
  $
  
  
  ===== ACTUAL OUTPUT:
  $ mpixlc_r -g -O3 -qstrict -qtm -qsmp=omp:speculative -c
  atomic_bug.c
  /opt/ibmcmp/vac/bg/12.1/bin/.orig/bgxlc_r: 1501-224 (S) fatal
  error in
  /opt/ibmcmp/vac/bg/12.1/exe/xlcentry: signal 11 received
  $
  
  
  ===== EXPECTED OUTPUT:
  Compiler should not abend.
  

Local fix

• n/a
  

Problem summary

• USERS AFFECTED:
  People using an invalid syntax form with compound statements of
  the open mp atomic pragma are affected by this issue.
  
  PROBLEM DESCRIPTION:
  The problem is that the pragma list flag says there is a pragma
  in the list and is mismatched with the actual list that has no
  pragmas.
  This causes a null pointer dereference.
  

Problem conclusion

• Do not use compound statements for the atomic pragma.
  

Temporary fix

Comments

APAR Information

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

  LI76943

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

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels

• RC10 PSY U856101

     UP C