这个数据结构怎么分析
struct exec
{
unsigned long a_info; /* Use macros N_MAGIC, etc for access */
unsigned a_text; /* length of text, in bytes */
unsigned a_data; /* length of data, in bytes */
unsigned a_bss; /* length of uninitialized data area for file, in bytes */
unsigned a_syms; /* length of symbol table data in file, in bytes */
unsigned a_entry; /* start address */
unsigned a_trsize; /* length of relocation info for text, in bytes */
unsigned a_drsize; /* length of relocation info for data, in bytes */
};