IZ32374: STRUCT PADDING BYTES NOT INIATILIZED

January 2009 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
April 2009 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
July 2009 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
November 2010 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
March 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
July 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
December 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
March 2012 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
January 2010 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
May 2010 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
August 2010 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
September 2008 PTF for XL C/C++ Enterprise Edition for AIX, V9.0

APAR status

• Closed as program error.

Error description

• Structures have been initialized differently in C and C++ and
  this is causing a problem to user's application.
  
  ==== TESTCASE:
  
  
  #include <stdio.h>
  #include <string.h>
  #include <stdlib.h>
  
  struct mystruct
  {
    char c1;
    int i;
  };
  
  static void copy_struct(struct mystruct* pMystruct_temp1)
  {
    struct mystruct mystruct_stack = {0};
    *pMystruct_temp1 = mystruct_stack;
    memset(&mystruct_stack,255,sizeof(struct mystruct));
  }
  
  int main(int argc, char** argv)
  {
    struct mystruct struct1;
    struct mystruct struct2;
    memset(&struct1,0,sizeof(struct mystruct));
    memset(&struct2,0,sizeof(struct mystruct));
    copy_struct(&struct1);
    copy_struct(&struct2);
  
    if(memcmp(&struct1,&struct2,sizeof(struct mystruct)))  /*
  where the
  dbx display is one*/
       printf("these structs are different\n");
    else
       printf("these structs are equal\n");
  
    return 0;
  }
  
  ===== ACTUAL OUTPUT:
  C:   these structures are equal
  C++: thes structures are not equal
  
  ===== EXPECTED OUTPUT:
  REQUIRED, FREEFORM
  C++: Struct should be initialized to null and the output should
  be: these structues are equal.
  

Local fix

• Use -qinitauto
  

Problem summary

• The C++ compiler does not zero fill pad bytes between struct
  members when initialized using braced list initializers.  This
  means that two different structs that are initialized using the
  same braced list initializer may not be byte wise identical.
  Although not required in the C++ standard, the xlc compiler as
  well as several other C++ vendors already do this.
  
  Users who initialize structures with braced list initializers
  are affected.
  

Problem conclusion

• Implemented -qxflag=zerofillpadbytes, which will zero fill pad
  bytes for auto variables that are POD structs.
  

Temporary fix

Comments

APAR Information

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

  IZ25953

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

Fix information

• Fixed component name

  XLC C++ AIX

• Fixed component ID

  5724S7100

Applicable component levels