PI67565: SEGMENTATION FAULT WITH STL <ALGORITHM> SORT

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A segmentation fault may be seen when using the STL <algorithm>
  sort() function.  A C++ standard-conforming change was made to
  the sort() function for performance reasons.  Code not
  conforming to the standard for sort() usage may encounter
  issues.
  
  
  Sorting data structures 16 elements in size or smaller is not
  affected.
  
  
  Per C++03 subclause 25.3 [lib.alg.sorting] paragraphs 3 and 4,
  the comparison operation should produce !comp(x, x) for all x.
  
  
  In the following test case, the Comp() comparison function uses
  (ret <= 0) to compare the elements, when a comparison of (ret <
  0) should be used to be standard-conforming.  This may affect
  comparison design in some scenarios.
  
  
  
     === TEST CASE ===
  
  #include <iostream>
  #include <cstring>
  #include <algorithm>
  
  using namespace std;
  
  struct element
  {
     char val1[100];
     char val2[100];
  };
  
  int compare_element(const struct element *p1,
                      const struct element *p2)
  {
   int ret = 0;
  
   if( !(ret = strcmp(((struct element *)p1)->val1,
        ((struct element *)p2)->val1))
          &&
       !(ret = strcmp(((struct element *)p1)->val2,
        ((struct element *)p2)->val2)) )
   {}
  
     return ret;
  }
  
  struct Comp
  {
   bool operator() (const struct element& x,
                    const struct element& y)
   {
     int ret = compare_element(&x, &y);
  
     if (ret <= 0) return(true); // SHOULD BE (ret < 0)
  
     return(false);
   }
  };
  
  int main()
  {
   static struct element array[] = {
      {"a","a"}, {"b","b"}, {"c","c"}, {"d","d"},
      {"e","e"}, {"f","f"}, {"g","g"}, {"h","h"},
      {"i","i"}, {"j","j"}, {"k","k"}, {"l","l"},
      {"m","m"}, {"n","n"}, {"o","o"}, {"p","p"},
      {"q","q"}
   };
  
   int nCount = sizeof(array)/sizeof(struct element);
   cout << "Array Size: " << nCount << endl;
  
   struct element *sort_array = (struct element *)malloc(nCount);
   for(int i = 0; i < nCount; i++) sort_array[i] = array[i];
  
   sort(sort_array, sort_array + nCount, Comp());
  
   return 0;
  }
  
  
  $ xlC test.cpp
  $ ./a.out
  Array Size: 17
  Segmentation fault (core dumped)
  $
  

Local fix

• Modify code to be standard-conforming.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users with non-standard conforming code.     *
  ****************************************************************
  * PROBLEM DESCRIPTION: Some non-standard conforming code may   *
  *                      encounter issues with thenew STL        *
  *                      <algorithm> sort() implementation       *
  *                      compared to theprevious implementation. *
  ****************************************************************
  * RECOMMENDATION: Apply the provided PTF.                      *
  *                                                              *
  ****************************************************************
  .
  

Problem conclusion

• Apply provided fix.
  

Temporary fix

Comments

APAR Information

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

  IV87935

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

  UI42168

Modules/Macros

• CRTEC128 CRTEC64  CRTE128N CRTHB001 CRTHT001 CRTIB001 CRTIT001
  

Fix information

• Fixed component name

  ANSI C++ CLASS

• Fixed component ID

  568819807

Applicable component levels

• R7A0 PSN UI42168

     UP16/11/02 P F611

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.