feat: add jobctlfg and jobtarget

user/killvictim.c

@@ -0,0 +1,38 @@
+#include "ulib.h"
+
+/*
+ * Only ever spawned by killtest.c. Attaches as the READ end of a shared
+ * pipe (userPipeCreate/userPipeAttach) that no writer will ever attach to,
+ * so the userRead call below can only ever return by being killed --
+ * proving threadKill (sched.c) genuinely recovers a process that would
+ * otherwise be stuck forever now that sysRead can really block (see
+ * pipe.h/vfs.h's shared-pipe machinery, added the same wave as this).
+ */
+
+int main(void)
+{
+    print("killvictim: start, pid=");
+    printDec(userGetpid());
+    print("\n");
+
+    long handle = userPipeCreate();
+    if (handle < 0) {
+        print("killvictim: FAIL pipe create\n");
+        return 1;
+    }
+
+    long fd = userPipeAttach(handle, 0);
+    if (fd < 0) {
+        print("killvictim: FAIL attach\n");
+        return 1;
+    }
+
+    print("killvictim: blocking on read forever\n");
+    char buffer[4];
+    userRead((int)fd, buffer, sizeof(buffer));
+
+    /* Only reached if userRead somehow returned on its own -- killtest.c
+       never writes to this pipe, so that would itself be a bug. */
+    print("killvictim: FAIL read returned without being killed\n");
+    return 1;
+}