libc: Add fork()

apps/init.c

@@ -37,12 +37,12 @@ int main()
 
     fprintf(stderr, "init is running as PID %d\n", getpid());
 
-    long ret = syscall(SYS_fork);
+    pid_t ret = fork();
 
     if (ret == 0)
     {
         char* argv[] = { "/bin/hello", "--help", NULL };
         execv("/bin/hello", argv);
     }
-    else { printf("my child is PID %ld!\n", ret); }
+    else { printf("my child is PID %d!\n", ret); }
 }

libc/include/unistd.h

@@ -18,7 +18,8 @@ extern "C"
 {
 #endif
 
-    pid_t fork();
+    /* Create a new process that is a clone of the current one. */
+    pid_t fork(void);
 
     /* Return the current process' process ID. */
     pid_t getpid(void);

libc/src/unistd.cpp

@@ -8,6 +8,12 @@ extern "C" long arch_invoke_syscall(long, uintptr_t, uintptr_t, uintptr_t, uintp
 
 extern "C"
 {
+    pid_t fork(void)
+    {
+        long rc = syscall(SYS_fork);
+        __errno_return(rc, int);
+    }
+
     pid_t getpid(void)
     {
         return (pid_t)syscall(SYS_getpid);