Anyone can explain the fields of vm_cont?

[Nala Ginrut]

I found that there's no any comments for the fields of struct vm_cont in
vm.h. Is there anyone kind enough to point me out?

 struct scm_vm_cont {
   SCM *sp;
   SCM *fp;
   scm_t_uint8 *ra, *mvra;
   scm_t_ptrdiff stack_size;
   SCM *stack_base;
   scm_t_ptrdiff reloc;
   scm_t_uint32 flags;
 };

I want to know the meaning of each fields, thanks!

PS: please don't reply me "it's unnecessary to know it for using Guile",
I want to know it anyway. ;-P

Best regards.