How do I use user_regs_struct on ARM processor in ptrace-based debugger

I am following the code in Chapter 3 of "Learning Linux Binary Analysis". The code is, "A simple ptrace-based debugger".

I am trying to write this in my Raspberry Pi 3, which has an ARM processor. I know that the error means that I have not included the correct header file, but I cannot find what the correct header file is.

I get this error message:

field ‘pt_reg’ has incomplete type struct user_regs_struct pt_reg

After doing some research, I found asm/ptrace.h, which includes some macros for the registers struct specific to ARM. Am I on the right track? How in the world can I make this work with an ARM processor?

Here are the headers:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <elf.h>
#include <sys/types.h>
#include <sys/user.h>
#include <sys/stat.h>
#include <sys/ptrace.h>
#include <sys/mman.h>

typedef struct handle {
  Elf64_Ehdr *ehdr;
  Elf64_Phdr *phdr;
  Elf64_Shdr *shdr;
  uint8_t *mem;
  char *symname;
  Elf64_Addr symaddr;
  struct user_regs_struct pt_reg;
  char *exec;
} handle_t;