IV05137: SEGMENTATION FAULT AT O3 WITHIN NESTED LOOP

August 2011 PTF for XL C/C++ for AIX, V11.1
November 2011 PTF for XL C/C++ for AIX, V11.1
January 2012 PTF for XL C for AIX, V11.1
January 2012 PTF for XL C/C++ for AIX, V11.1
April 2012 PTF for XL C for AIX, V11.1
April 2012 PTF for XL C/C++ for AIX, V11.1
July 2012 PTF for XL C/C++ for AIX, V11.1
October 2012 PTF for XL C/C++ for AIX, V11.1
October 2012 PTF for XL C for AIX, V11.1
February 2013 PTF for XL C for AIX, V11.1
February 2013 PTF for XL C/C++ for AIX, V11.1
XL C/C++ for AIX Fix Pack 14 (May 2013 PTF) for 11.1
XL C for AIX Fix Pack 14 (May 2013 PTF) for 11.1
XL C/C++ for AIX Fix Pack 15 (August 2013 PTF) for 11.1
XL C for AIX Fix Pack 15 (August 2013 PTF) for 11.1
XL C/C++ for AIX Fix Pack 16 (November 2013 PTF) for 11.1
XL C for AIX Fix Pack 17 (February 2014 PTF) for 11.1
XL C/C++ for AIX Fix Pack 17 (February 2014 PTF) for 11.1
XL C/C++ for AIX Fix Pack 18 (May 2014 PTF) for 11.1
XL C/C++ for AIX Fix Pack 19 (August 2014 PTF) for 11.1
XL C/C++ for AIX Fix Pack 20 (November 2014 PTF) for 11.1
XL C for AIX Fix Pack 21 (April 2015 PTF) for 11.1
XL C/C++ for AIX Fix Pack 21 (April 2015 PTF) for 11.1
XL C/C++ for AIX Fix Pack 22 (September 2015 PTF) for 11.1
XL C for AIX Fix Pack 23 (March 2016 PTF) for 11.1
XL C/C++ for AIX Fix Pack 23 (March 2016 PTF) for 11.1
XL C for AIX Fix Pack 24 (September 2016 PTF) for 11.1
XL C/C++ for AIX Fix Pack 24 (September 2016 PTF) for 11.1
August 2011 PTF for XL C for AIX, V11.1
November 2011 PTF for XL C for AIX, V11.1
July 2012 PTF for XL C for AIX, V11.1
XL C for AIX Fix Pack 16 (November 2013 PTF) for 11.1
XL C for AIX Fix Pack 18 (May 2014 PTF) for 11.1
XL C for AIX Fix Pack 19 (August 2014 PTF) for 11.1
XL C for AIX Fix Pack 20 (November 2014 PTF) for 11.1
XL C for AIX Fix Pack 22 (September 2015 PTF) for 11.1

APAR status

• Closed as program error.

Error description

• A segmentation fault is encountered at -O3 optimization whe
  runnning a test case that contains a nested loop.
  
  ==== Test case:
  test.c:
  #include <stdlib.h>
  #include <stdio.h>
  
  typedef struct {
    void *params;
  } Temp;
  
  void * get_params(Lattice *lat)
  {
    return lat->params;
  }
  
  void get_loop(Temp *lat, int x[], int nd, int index)
  {
    void *p = get_params(lat);
  
    for(int i=0; i<nd; i++) {
      x[i] = index;
    }
  }
  
  void CreateNestedBlock(int nd, Lattice *lat)
  {
    for(int b=0; b<2; b++) {
     int xf[nd];
      for(int j=0; j<1; j++) {
        get_loop(lat, xf, nd, j);
      }
    }
  }
  
  int main(int argc, char *argv[])
  {
    int ndim = 4;
    Temp lat;
    lat.params = NULL;
  
    printf("starting\n");
    CreateNestedBlock(ndim, &lat);
    printf("done\n");
  
    return 0;
  }
  
  
  ==== Observed Output:
  $ xlc -O3 test.c
  staring
  Segmentation fault
  $
  

Local fix

• Use a lower optimization level.
  

Problem summary

• PROBLEM DESCRIPTION:
  Segmentation fault at -O3 when returning from a function.
  
  USERS AFFECTED:
  Users of optimization levels -O3 or higher.
  

Problem conclusion

• Intermediate generated code was incorrectly moved outside of an
  internal optimized loop. Resulting in the corruption of the
  return address of the function. This fix involves ensuring that
  this particular block of code is not moved outside of the loop.
  

Temporary fix

Comments

APAR Information

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

  LI76071

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

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5724X1200

Applicable component levels