IJ06072: COMPILER GENERATING INCORRECT CODE LEADING TO MEMORY FAULT

XL C for AIX, V13.1.3.5 Fix Pack (July 2018)
XL C/C++ for AIX, V13.1.3.5 Fix Pack (July 2018)
XL C for AIX, V13.1.3.6 Fix Pack (May 2019)
XL C/C++ for AIX, V13.1.3.6 Fix Pack (May 2019)

APAR status

• Closed as program error.

Error description

• The problem is that the compiler is generating assembler code
  that crashes.
  
  ===== COMPILE COMMAND:
  $ cc_r  -o test 157849.c
  
  ===== TESTCASE:
  $ cat 157849.c
  #include <strings.h>
  #include <stdio.h>
  #include <fcntl.h>
  #include <errno.h>
  #include <sys/types.h>
  #include <sys/mman.h>
  
  typedef unsigned char uchar;
  
  /* Calendar date/time structure. */
  #define BASE_YEAR 1900
  typedef struct _dt
  {
    uchar   year;                   /* Years since BASE_YEAR (0 -
  255). */
    uchar   mon;                    /* Month within year (1 - 12).
  */
    uchar   day;                    /* Day within month (1 - 31).
  */
    uchar   hour;                   /* Hours within day (0 - 23).
  */
    uchar   min;                    /* Minutes within hour (0 -
  59).    */
    uchar   sec;                    /* Seconds within minute (0 -
  59).  */
  } DateTime;
  
  static int printDate( DateTime d );
  
  int main( int argc, char *argv[] )
  {
    int rc = 0;
    int  i = 0;
    int fd = -1;
    int dateCount = 0;
    char  *map = NULL;
    DateTime *dates = NULL;
  
    fd = open( argv[1], O_RDWR );
    if ( fd > 0 )
    {
      map = mmap( NULL, 4096, PROT_READ|PROT_WRITE,
  MAP_FILE|MAP_PRIVATE,
                  fd, 0 );
      if ( map != NULL )
      {
        /* get the date count */
  /*    dateCount = *(int *)map; */
        dateCount = 682;
  
        /* point to the array of dates, which begins immediately
  after the
           count */
        dates     =  (DateTime *)(map + sizeof(int) );
  
        /* iterate over the entire array and print out each date
  */
        if ( dateCount > 4096/sizeof(DateTime) )
          fprintf( stderr, "Count value of %d is too big.\n",
  dateCount );
        else
        {
          for ( i=0; i<dateCount; i++ )
            printDate( dates[i] ); /* << crashes when the last
  date is at
                                      << the end of the mmapped
  region */
        }
      }
    }
    else
    {
      rc = errno;
      fprintf( stderr, "Error %d opening %s.\n", rc, argv[1] );
    }
  
    if ( map != 0 )
      munmap( map, 4096 );
  
    return rc;
  } /* main */
  static int printDate( DateTime d )
  {
    fprintf( stdout, "%04d:%02d:%02d\n", d.year+BASE_YEAR, d.mon,
  d.day );
    return 0;
  } /* printDate */
  $
  
  
  ===== ACTUAL OUTPUT:
  $ ./test 157849.dat
  .
  .
  .
  1900:00:00
  1900:00:00
  1900:00:00
  1900:00:00
  1900:00:00
  1900:00:00
  Memory fault
  $
  
  
  ===== EXPECTED OUTPUT:
  Should not crash at runtime
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users who write code loading arguments ending at protected page
  boundary are affected by this issue
  
  PROBLEM DESCRIPTION:
  Users will experience a runtime memory error when loading
  arguments ending at protected page boundary
  

Problem conclusion

• The compiler has been changed to force the load arguments ending
   at protected page boundary with the exact size to void memory
  fault.
  

Temporary fix

Comments

APAR Information

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

• 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

• RD13 PSY

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