IZ78417: C COMPILER ISSUE WITH CONST INT ARRAY SIZES

Fixes are available

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 number
IZ78417
Reported component name
XL C FOR AIX
Reported component ID
5724X1200
Reported release
B10
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2010-06-30
Closed date
2010-06-30
Last modified date
2010-06-30

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 FOR AIX
Fixed component ID
5724X1200

Applicable component levels

[{"Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSGH2K","label":"XL C for AIX"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1"}]

Document Information

Modified date:
06 October 2021

Tips

IZ78417: C COMPILER ISSUE WITH CONST INT ARRAY SIZES

Fixes are available

Subscribe

APAR status

Closed as program error.

Error description

Local fix

Problem summary

Problem conclusion

Temporary fix

Comments

APAR Information

APAR number

Reported component name

Reported component ID

Reported release

Status

PE

HIPER

Special Attention

Submitted date

Closed date

Last modified date

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

Fixed component ID

Applicable component levels

Document Information

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