7.3.5 Structures

Check the internal data structures in an applications for holes. Use extra padding between fields in the structure to meet alignment requirements. This extra padding is allocated when long or pointer fields grow to 64 bits for the LP64 data-type model. In the 64-bit compilation environment on SPARC platforms, all types of structures are aligned to the size of the largest member within them. When you repack a structure, follow the simple rule of moving the long and pointer fields to the beginning of the structure. Consider the following structure definition:

struct bar {
   int i;
   long j;
   int k;
   char *p;
};   /* sizeof (struct bar) = 32 */

Here is the same structure with the long and pointer data types defined at the beginning of the structure:

struct bar {
  char *p;
  long j;
  int i;
  int k;
};   /* sizeof (struct bar) = 24 */