Chapter 10

1. I’ll let you do this on your own.
2. Return an integer
   • test_f.c

     // Test f() function.
     
     #include <stdio.h>
     #include "f.h"
     
     int main(void)
     {
         int return_value;
         return_value = f();
         printf("f returned %i.\n", return_value);
     
         return 0;
     }
     

   • f.h

     // Return 0.
     
     #ifndef F_H
     #define F_H
     int f(void);
     #endif
     

   • f.s

     // Minimum components of a C function, in assembly language
     // returns 0
     
             .arch   armv8-a
             .text
             .align  2
             .global f
             .type   f, %function
     f:
             mov     w0, wzr         // return 0;
             ret
     

3. Return three integers.
   • test_ints.c

     // Test three functions that return ints.
     
     #include <stdio.h>
     #include "twelve.h"
     #include "thirty_four.h"
     #include "fifty_six.h"
     
     int main(void)
     {
         int return1, return2, return3;
     
         return1 = twelve();
         return2 = thirty_four();
         return3 = fifty_six();
         printf("The returned ints are: %i, %i, and %i.\n",
               return1, return2, return3);
     
         return 0;
     }
     

   • twelve.h

     // Return 12.
     
     #ifndef TWELVE_H
     #define TWELVE_H
     int twelve(void);
     #endif
     

   • twelve.s

     // Return 12.
     
             .arch   armv8-a
             .text
             .align  2
             .global twelve
             .type   twelve, %function
     twelve:
             mov     w0, 12
             ret
     

   • thirty_four.h

     // Return 34.
     
     #ifndef THIRTY_FOUR_H
     #define THIRTY_FOUR_H
     int thirty_four(void);
     #endif
     

   • thirty_four.s

     // Return 34.
     
             .arch   armv8-a
             .text
             .align  2
             .global thirty_four
             .type   thirty_four, %function
     thirty_four:
             mov     w0, 34
             ret
     

   • fifty_six.h

     // Return 56.
     
     #ifndef FIFTY_SIX_H
     #define FIFTY_SIX_H
     int fifty_six(void);
     #endif
     

   • fifty_six.s

     // Return 56.
     
             .arch   armv8-a
             .text
             .align  2
             .global fifty_six
             .type   fifty_six, %function
     fifty_six:
             mov     w0, 56
             ret
     

4. Return three characters.
   • test_chars.c

     // Test three functions that return chars.
     
     #include <stdio.h>
     #include "exclaim.h"
     #include "upper_oh.h"
     #include "tilde.h"
     
     int main(void)
     {
         unsigned char return1, return2, return3;
     
         return1 = exclaim();
         return2 = upper_oh();
         return3 = tilde();
         printf("The returned chars are: %c, %c, and %c.\n",
               return1, return2, return3);
     
         return 0;
     }
     

   • exclaim.h

     // Return '!'.
     
     #ifndef EXCLAIM_H
     #define EXCLAIM_H
     char exclaim(void);
     #endif
     

   • exclaim.s

     // Return '!'.
     
             .arch   armv8-a
             .text
             .align  2
             .global exclaim
             .type   exclaim, %function
     exclaim:
             mov     w0, '!'
             ret
     

   • upper_oh.h

     // Return 'O'.
     
     #ifndef UPPER_OH_H
     #define UPPER_OH_H
     unsigned char upper_oh(void);
     #endif
     

   • upper_oh.s

     // Return 'O'.
     
             .arch   armv8-a
             .text
             .align  2
             .global upper_oh
             .type   upper_oh, %function
     upper_oh:
             mov     w0, 'O'
             ret
     

   • tilde.h

     // Return '~'.
     
     #ifndef TILDE_H
     #define TILDE_H
     unsigned char tilde(void);
     #endif
     

   • tilde.s

     // Return '~'.
     
             .arch   armv8-a
             .text
             .align  2
             .global tilde
             .type   tilde, %function
     tilde:
             mov     w0, '~'
             ret