diff -ruN kozos09/Makefile kozos10/Makefile
--- kozos09/Makefile	Wed Nov  7 21:55:48 2007
+++ kozos10/Makefile	Wed Nov  7 21:55:48 2007
@@ -1,4 +1,5 @@
 OBJS += thread.o syscall.o outlog.o extintr.o idle.o
+OBJS += stubd.o stublib.o i386-stub.o
 OBJS += main.o clock.o telnetd.o httpd.o
 TARGET ?= koz
 CC ?= gcc
diff -ruN kozos09/kozos.h kozos10/kozos.h
--- kozos09/kozos.h	Wed Nov  7 21:55:48 2007
+++ kozos10/kozos.h	Wed Nov  7 21:55:48 2007
@@ -18,19 +18,23 @@
 int kz_timer(int msec);
 int kz_pending();
 int kz_setsig(int signo);
+int kz_debug(int sockt);
 void *kz_memalloc(int size);
 int kz_memfree(void *p);
 
 /* library */
 void kz_start(kz_func func, char *name, int pri, int argc, char *argv[]);
+void kz_break();
 
 /* general thread */
 extern int outlog_id;
 extern int extintr_id;
 extern int idle_id;
+extern int stubd_id;
 int outlog_main(int argc, char *argv[]);
 int extintr_main(int argc, char *argv[]);
 int idle_main(int argc, char *argv[]);
+int stubd_main(int argc, char *argv[]);
 
 /* user thread */
 extern int clock_id;
diff -ruN kozos09/main.c kozos10/main.c
--- kozos09/main.c	Wed Nov  7 21:55:48 2007
+++ kozos10/main.c	Wed Nov  7 21:55:48 2007
@@ -6,7 +6,8 @@
 int mainfunc(int argc, char *argv[])
 {
   extintr_id  = kz_run(extintr_main,  "extintr",   1, 0, NULL);
-  outlog_id   = kz_run(outlog_main,   "outlog",    2, 0, NULL);
+  stubd_id    = kz_run(stubd_main,    "stubd",     2, 0, NULL);
+  outlog_id   = kz_run(outlog_main,   "outlog",    3, 0, NULL);
   idle_id     = kz_run(idle_main,     "idle",     31, 0, NULL);
   clock_id    = kz_run(clock_main,    "clock",     7, 0, NULL);
   telnetd_id  = kz_run(telnetd_main,  "telnetd",   8, 0, NULL);
diff -ruN kozos09/syscall.c kozos10/syscall.c
--- kozos09/syscall.c	Wed Nov  7 21:55:48 2007
+++ kozos10/syscall.c	Wed Nov  7 21:55:48 2007
@@ -112,6 +112,14 @@
   return param.un.setsig.ret;
 }
 
+int kz_debug(int sockt)
+{
+  kz_syscall_param_t param;
+  param.un.debug.sockt = sockt;
+  kz_syscall(KZ_SYSCALL_TYPE_DEBUG, &param);
+  return param.un.debug.ret;
+}
+
 void *kz_memalloc(int size)
 {
   kz_syscall_param_t param;
diff -ruN kozos09/syscall.h kozos10/syscall.h
--- kozos09/syscall.h	Wed Nov  7 21:55:48 2007
+++ kozos10/syscall.h	Wed Nov  7 21:55:48 2007
@@ -16,6 +16,7 @@
   KZ_SYSCALL_TYPE_TIMER,
   KZ_SYSCALL_TYPE_PENDING,
   KZ_SYSCALL_TYPE_SETSIG,
+  KZ_SYSCALL_TYPE_DEBUG,
   KZ_SYSCALL_TYPE_MEMALLOC,
   KZ_SYSCALL_TYPE_MEMFREE,
 } kz_syscall_type_t;
@@ -72,6 +73,10 @@
       int signo;
       int ret;
     } setsig;
+    struct {
+      int sockt;
+      int ret;
+    } debug;
     struct {
       int size;
       void *ret;
diff -ruN kozos09/telnetd.c kozos10/telnetd.c
--- kozos09/telnetd.c	Wed Nov  7 21:55:48 2007
+++ kozos10/telnetd.c	Wed Nov  7 21:55:48 2007
@@ -42,9 +42,11 @@
 
     if (!strncmp(buffer, "echo", 4)) {
       write(s, buffer + 4, strlen(buffer + 4));
-    } else if (!strncmp(buffer, "break", 5)) {
+    } else if (!strncmp(buffer, "down", 4)) {
       int *nullp = NULL;
       *nullp = 1;
+    } else if (!strncmp(buffer, "break", 5)) {
+      kz_break();
     } else if (!strncmp(buffer, "date", 4)) {
       time_t t;
       t = time(NULL);
diff -ruN kozos09/thread.c kozos10/thread.c
--- kozos09/thread.c	Wed Nov  7 21:55:48 2007
+++ kozos10/thread.c	Wed Nov  7 21:55:48 2007
@@ -9,6 +9,7 @@
 #include "kozos.h"
 #include "syscall.h"
 #include "thread.h"
+#include "stublib.h"
 
 #define SIG_NUM 32
 #define STACK_SIZE 0x8000
@@ -24,6 +25,7 @@
 static jmp_buf intr_env;
 static kz_timebuf *timers;
 static kz_thread *sigcalls[SIG_NUM];
+static int debug_sockt = 0;
 
 kz_thread *current;
 
@@ -298,6 +300,14 @@
     sendmsg(sigcalls[signo], 0, 0, NULL);
 }
 
+static int thread_debug(int sockt)
+{
+  debug_sockt = sockt;
+  stub_init(sockt);
+  putcurrent();
+  return 0;
+}
+
 static void *thread_memalloc(int size)
 {
   putcurrent();
@@ -357,6 +367,9 @@
   case KZ_SYSCALL_TYPE_SETSIG:
     p->un.setsig.ret = thread_setsig(p->un.setsig.signo);
     break;
+  case KZ_SYSCALL_TYPE_DEBUG:
+    p->un.debug.ret = thread_debug(p->un.debug.sockt);
+    break;
   case KZ_SYSCALL_TYPE_MEMALLOC:
     p->un.memalloc.ret = thread_memalloc(p->un.memalloc.size);
     break;
@@ -397,7 +410,9 @@
   case SIGSEGV:
   case SIGTRAP:
   case SIGILL:
-    {
+    if (debug_sockt) {
+      stub_proc(current, signo);
+    } else {
       fprintf(stderr, "error thread \"%s\"\n", current->name);
       /* ダウン要因発生により継続不可能なので，スリープ状態にする*/
       getcurrent();
@@ -468,4 +483,13 @@
 
   /* ここには返ってこない */
   abort();
+}
+
+void kz_break()
+{
+  /*
+   * スタブ付属の breakpoint() でうまくブレークできないので，
+   * トラップシグナルを上げてブレークする．
+   */
+  kill(getpid(), SIGTRAP);
 }