LI75586: C COMPILER ISSUE WITH CONST INT ARRAY SIZES

June 2011 Update for XL C/C++ for Linux, V10.1
XL C/C++ for Linux Fix Pack 8 (January 2014 Update) for 10.1
August 2010 Update for XL C/C++ for Linux, V10.1
January 2011 Update for XL C/C++ for Linux, V10.1
January 2012 Update for XL C/C++ for Linux, V10.1
July 2012 Update for XL C/C++ for Linux, V10.1

APAR status

• Closed as program error.

Error description

• In c99, when a variable declared as 'const int' is used as size
  in a local array declaration, the size determination and space
  allocation under some conditions is mishandled, and space is not
  allocated.
  
  ===== COMPILE COMMAND:
  xlc test.c
  
  $ cat xlc-bug.c
  #include <stdio.h>
  #include <string.h>
  
  enum { CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE = 50 };
  typedef char
  crdappu_cds_names_token_t[CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE];
  
  void write_stuff(crdappu_cds_names_token_t names[]);
  void test_one();
  void test_two();
  
  int main(int argc, char *argv[]){
    if ( argc <= 1) {
      printf("calling test_two\n");
      test_two();
      printf("back from test_two\n");
    }
    else {
      printf("calling test_one\n");
      test_one();
      printf("back test_one\n");
    }
  
    return 0;
  }
  
  
  /*
  ** If we use enum it works
  enum { cdsNamesTokenArrSz = 100 };
  **  With the following, test_two crashes
  **  if it executes before test_one executes
  */
  const int cdsNamesTokenArrSz = 100;
  
  void test_one(){
    char my_array[CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE];
    char my_array1[CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE];
    crdappu_cds_names_token_t
  cdsNamesTokenArr[cdsNamesTokenArrSz];
  printf("sizeof my_array = %ld\n", sizeof my_array);
  printf("sizeof my_array1 = %ld\n", sizeof my_array1);
  printf("sizeof cdsNamesTokenArr = %ld\n", sizeof
  cdsNamesTokenArr);
    memset(my_array,' ',sizeof my_array);
    memset(my_array1,' ',sizeof my_array1);
    write_stuff(cdsNamesTokenArr);
  printf("after write_stuff call\n");
    memset(my_array,'1',sizeof my_array);
  printf("after memset to my_array\n");
    memset(my_array1,'1',sizeof my_array1);
  printf("after memset to my_array1\n");
  }
  
  void test_two(){
    char my_array[CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE];
    char my_array1[CRDAPPU_CDS_NAMES_MAX_TOKEN_SIZE];
    crdappu_cds_names_token_t
  cdsNamesTokenArr[cdsNamesTokenArrSz];
  printf("sizeof my_array = %ld\n", sizeof my_array);
  printf("sizeof my_array1 = %ld\n", sizeof my_array1);
  printf("sizeof cdsNamesTokenArr = %ld\n", sizeof
  cdsNamesTokenArr);
    memset(my_array,' ',sizeof my_array);
    memset(my_array1,' ',sizeof my_array1);
    write_stuff(cdsNamesTokenArr);
  printf("after write_stuff call\n");
    memset(my_array,'1',sizeof my_array);
  printf("after memset to my_array\n");
    memset(my_array1,'1',sizeof my_array1);
  printf("after memset to my_array1\n");
  }
  
  void write_stuff(  crdappu_cds_names_token_t names[]){
    int i,k;
    printf("write_stuff starts\n");
  printf("sizeof names = %ld\n", sizeof names);
  printf("sizeof names[0] = %ld\n", sizeof names[0]);
  printf("sizeof(crdappu_cds_names_token_t) = %ld\n",
  sizeof(crdappu_cds_names_token_t));
    for(i=0;i<100;i++){
      for(k=0;k<sizeof(crdappu_cds_names_token_t);k++){
        names[i][k]='L';
  
      }
  
    }
    printf("write_stuff ends\n");
  }
  $
  
  
  ===== ACTUAL OUTPUT:
  $
  /.../torolab.ibm.com/fs/projects/vabld/run/vacpp/101_com/aix/dai
  ly/latest/bin/xlc xlc-bug.c
  $ ./a.out
  calling test_two
  sizeof my_array = 50
  sizeof my_array1 = 50
  sizeof cdsNamesTokenArr = 0
  write_stuff starts
  sizeof names = 4
  sizeof names[0] = 50
  sizeof(crdappu_cds_names_token_t) = 50
  write_stuff ends
  after write_stuff call
  after memset to my_array
  after memset to my_array1
  Segmentation fault
  $
  
  
  
  ===== EXPECTED OUTPUT:
  $ ./a.out
  calling test_two
  sizeof my_array = 50
  sizeof my_array1 = 50
  sizeof cdsNamesTokenArr = 5000
  write_stuff starts
  sizeof names = 4
  sizeof names[0] = 50
  sizeof(crdappu_cds_names_token_t) = 50
  write_stuff ends
  after write_stuff call
  after memset to my_array
  after memset to my_array1
  back from test_two
  $
  

Local fix

• Compile the program as C++.
  

Problem summary

• USERS AFFECTED:
  Any users using variable length arrays at different scopes in
  different orders from sequential order maybe affected by this
  issue.
  
  PROBLEM DESCRIPTION:
  Variable length arrays that are accessed or defined in
  different a order than code order and at different scopes will
  cause invalid runtime values or protection exceptions.
  

Problem conclusion

• The compiler has been modified so that the variable length
  array size data is scope dependent. Any time a the VLA goes out
  of scope, the size data is cleared and
  so it will be recalculated upon new VLA definition when it
  comes into scope again.
  

Temporary fix

Comments

APAR Information

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

  IZ69754

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

Fix information

• Fixed component name

  XL C/C++ SLES10

• Fixed component ID

  5724U8300

Applicable component levels

• RA10 PSN IZ69754

     UP06/09/13