add sys_printchar

kern/arch/mips/syscall/syscall.c

@@ -110,6 +110,10 @@ void syscall(struct trapframe *tf) {
     thread_exit();
     break;
 
+  case SYS_printchar:
+    err = sys_printchar((char)tf->tf_a0);
+    break;
+
     /* Add stuff here */
 
   default:

kern/conf/conf.kern

@@ -379,6 +379,7 @@ file      vfs/devnull.c
 file      syscall/loadelf.c
 file      syscall/runprogram.c
 file      syscall/time_syscalls.c
+file      syscall/printchar.c
 
 #
 # Startup and initialization

kern/include/kern/syscall.h

@@ -94,6 +94,7 @@
 // #define SYS_getpriority 38
 // #define SYS_setpriority 39
 //                               (process groups, sessions, and job control)
+#define SYS_printchar 41
 // #define SYS_getpgid    40
 // #define SYS_setpgid    41
 // #define SYS_getsid     42

kern/include/syscall.h

@@ -57,4 +57,6 @@ __DEAD void enter_new_process(int argc, userptr_t argv, userptr_t env,
 int sys_reboot(int code);
 int sys___time(userptr_t user_seconds, userptr_t user_nanoseconds);
 
+int sys_printchar(char c);
+
 #endif /* _SYSCALL_H_ */

kern/syscall/printchar.c

@@ -0,0 +1,7 @@
+#include <types.h>
+#include <lib.h>
+#include <syscall.h>
+int sys_printchar(char c) {
+  kprintf("%c", c);
+  return 0;
+}