I added smes and rmes system calls to a7out and wrote some code

in src/other/fork_test.s to test it. It's not working quite right
yet, we keep getting wait() returning -1 in a7out even though there
is a child process.

src/other/fork_test.s

@@ -7,14 +7,33 @@ main:
 child:
    lac d1
    sys write; childmsg;  3
+   sys smes
    sys exit
 
 parent:
+   dac pid	" save the childs pid
    lac d1
    sys write; parentmsg; 4
+
+   sys rmes	" wait for the child to exit
+   sad pid	" did we get the same pid back?
+     jmp ok
+
+wrong:
+   lac d1
+   sys write; badpid;  4
+   sys exit
+
+ok:
+   lac d1
+   sys write; goodpid;  4
    sys exit
 
 d1: 1		" stdout fd
+pid: 0		" child's pid
 
 parentmsg: <pa>; <re>; <nt>; 012000
 childmsg:  <ch>; <il>; <d 012
+
+goodpid: <go>; <od>; <pi>; <d 012
+badpid: <ba>; <dp>; <id>; 012000

tools/a7out

@@ -537,6 +537,8 @@ sub cal {
         17 => \&sys_chdir,
         18 => \&sys_chmod,
         19 => \&sys_chown,
+        27 => \&sys_rmes,
+        28 => \&sys_smes,
         29 => \&sys_fork,
     );
 
@@ -551,7 +553,7 @@ sub cal {
 
 # Exit system call
 sub sys_exit {
-    dprintf("exit system call\n");
+    dprintf("exit system call, pid %06o\n", $$);
     exit(0);
 }
 
@@ -568,13 +570,35 @@ sub sys_fork {
 
     # Fork and get the child's process-id back, or zero if we are the child
     my $pid= fork();
-    $AC= $pid;
+    $AC= $pid & MAXINT;
+    dprintf( "fork, got id %06o\n", $AC);
 
     # The parent returns back to PC+1, the child returns to PC+2
     $PC += ($pid) ? 1 : 2;
     return;
 }
 
+# Smes system call. Because we fake rmes with wait(),
+# there is no need for sms. When the child does
+# sys exit, that's going to wake wait() up and do the
+# rmes anyway.
+sub sys_smes {
+    # For now, do nothing
+    dprintf("smes system call\n");
+    $PC += 1;
+    return;
+}
+
+# Rmes system call. We simply call wait and
+# return the process-id in AC
+sub sys_rmes {
+    my $pid= wait();
+    dprintf("rmes system call, got pid $pid\n");
+    $AC= $pid & MAXINT;
+    $PC += 1;
+    return;
+}
+
 # Close system call
 sub sys_close {