IZ87561: ASSERT FAILURE WHEN COMPILED WITH -G

May 2012 PTF for XL C/C++ for AIX, V10.1
January 2013 PTF for XL C for AIX, V10.1
January 2013 PTF for XL C/C++ for AIX, V10.1
XL C/C++ for AIX Fix Pack 18 (July 2013 PTF) for 10.1
XL C/C++ for AIX Fix Pack 19 (October 2013 PTF) for 10.1
XL C/C++ for AIX Fix Pack 21 (October 2015 PTF) for 10.1
XL C for AIX Fix Pack 21 (October 2015 PTF) for 10.1
February 2011 PTF for XL C for AIX, V10.1
May 2011 PTF for XL C/C++ for AIX, V10.1
May 2011 PTF for XL C for AIX, V10.1
October 2011 PTF for XL C/C++ for AIX, V10.1
October 2011 PTF for XL C for AIX, V10.1
February 2012 PTF for XL C for AIX, V10.1
February 2012 PTF for XL C/C++ for AIX, V10.1
May 2012 PTF for XL C for AIX, V10.1
September 2012 PTF for XL C for AIX, V10.1
September 2012 PTF for XL C/C++ for AIX, V10.1
XL C for AIX Fix Pack 18 (July 2013 PTF) for 10.1
XL C for AIX Fix Pack 19 (October 2013 PTF) for 10.1
XL C for AIX Fix Pack 20 (October 2014 PTF) for 10.1
XL C/C++ for AIX Fix Pack 20 (October 2014 PTF) for 10.1

APAR status

• Closed as program error.

Error description

• The following test program shows problems while
  compiling with V10.1 and option -g. The program encounters an
  assert.
  
  ===== COMPILE COMMAND:
  cc -g -qlanglvl=extc99 -l pthread myiov.c
  
  ===== TESTCASE:
  $ cat myiov.c
  #include <assert.h>
  #include <pthread.h>
  #include <sys/uio.h>
  #include <stdio.h>
  
  
  
  static void
  doit( const unsigned runs )
  {
      const unsigned e1 = 0xdeadbeef;
  
  
      const unsigned dimension = ((runs+1)%10)*2;
      struct iovec myiov[dimension];
  
      for (unsigned i=0; i< (dimension); i++ ) {
          myiov[i].iov_base = &i;
          myiov[i].iov_len  = i;
          assert( e1 == 0xdeadbeef );
          usleep(runs%10);
          for (unsigned k=0;k< dimension; k++) {
              assert( (void*)&e1 != (void*)&myiov[k] );
          }
      }
  }
  
  static void* body(void* v)
  {
      unsigned runs = 0;
      while ( v ) {
          doit( ++runs );
  
          if ( runs %1000 == 0 )
               printf("runs %04u %u\n", pthread_self(), runs );
  
      }
      return v;
  }
  
  int
  main( int argc __attribute__((unused)), char *argv[]
  __attribute__((unused)) )
  {
  
      unsigned runs = 2467638383;
  
      for (unsigned i=0; i<10; i++) {
          pthread_t thread_id;
          const int rc = pthread_create( &thread_id, NULL, body,
  &runs  );
          assert( rc == 0 );
      }
      body(&runs);
      return 0;
  }
  
  $
  
  
  ===== ACTUAL OUTPUT:
  $ ./a.out
  runs 0258 1000
  runs 0515 1000
  runs 1543 1000
  runs 0001 1000
  .
  .
  .
  runs 1029 9000
  runs 2057 9000
  Assertion failed: (void*)&e1 != (void*)&myiov[k], file  myiov.c,
  line 23
  IOT/Abort trap
  $
  
  ===== EXPECTED OUTPUT:
  $ ./a.out
  runs 0515 1000
  runs 1543 1000
  runs 2571 1000
  runs 1800 1000
  runs 2057 1000
  runs 1286 1000
  runs 2314 1000
  .
  .
  .
  //should not trap
  

Local fix

• n/a
  

Problem summary

• USERS AFFECTED:
  User of variable length arrays together with -g may be affected
  by this issue.
  
  PROBLEM DESCRIPTION:
  There occurs a race condition with variable length arrray code
  in debug mode that causes the application to core.
  

Problem conclusion

• The compiler has been fixed to change the way temporaries for
  variable length arrays are generated to avoid the race
  condition when -g is used.
  

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:

  IZ91495 LI75832 LI75860 LI76098

Fix information

• Fixed component name

  XL C AIX

• Fixed component ID

  5724U8000

Applicable component levels