add sys_add_three_integers

kern/arch/mips/syscall/syscall.c

@@ -114,6 +114,12 @@ void syscall(struct trapframe *tf) {
     err = sys_printchar((char)tf->tf_a0);
     break;
 
+  case SYS_add_three_integers:
+    err = sys_add_three_integers((int)tf->tf_a0, (int)tf->tf_a1, (int)tf->tf_a2,
+                                 &retval);
+    kprintf("%d\n", retval);
+    break;
+
     /* Add stuff here */
 
   default:

kern/conf/conf.kern

@@ -380,6 +380,7 @@ file      syscall/loadelf.c
 file      syscall/runprogram.c
 file      syscall/time_syscalls.c
 file      syscall/printchar.c
+file      syscall/add_three_integers.c
 
 #
 # Startup and initialization

kern/include/kern/syscall.h

@@ -95,6 +95,7 @@
 // #define SYS_setpriority 39
 //                               (process groups, sessions, and job control)
 #define SYS_printchar 41
+#define SYS_add_three_integers 42
 // #define SYS_getpgid    40
 // #define SYS_setpgid    41
 // #define SYS_getsid     42

kern/include/syscall.h

@@ -59,4 +59,6 @@ int sys___time(userptr_t user_seconds, userptr_t user_nanoseconds);
 
 int sys_printchar(char c);
 
+int sys_add_three_integers(int a, int b, int c, int *ret);
+
 #endif /* _SYSCALL_H_ */

kern/syscall/add_three_integers.c

@@ -0,0 +1,8 @@
+#include <types.h>
+#include <lib.h>
+#include <syscall.h>
+
+int sys_add_three_integers(int a, int b, int c, int *ret) {
+  *ret = a + b + c;
+  return 0;
+}