diff -ruN kozos29/kozos.h kozos30/kozos.h
--- kozos29/kozos.h	Mon Dec 17 21:53:06 2007
+++ kozos30/kozos.h	Mon Dec 17 22:12:16 2007
@@ -4,6 +4,7 @@
 #include "configure.h"
 
 typedef int (*kz_func)(int argc, char *argv[]);
+typedef void (*kz_handler)(int signo);
 
 /* syscall */
 int kz_run(kz_func func, char *name, int pri, int argc, char *argv[]);
@@ -17,6 +18,7 @@
 int kz_recv(int *idp, char **pp);
 int kz_timer(int msec);
 int kz_pending();
+int kz_sethandler(int signo, kz_handler handler);
 int kz_setsig(int signo);
 int kz_debug(int sockt);
 void *kz_kmalloc(int size);
diff -ruN kozos29/syscall.c kozos30/syscall.c
--- kozos29/syscall.c	Mon Dec 17 21:53:06 2007
+++ kozos30/syscall.c	Mon Dec 17 22:11:57 2007
@@ -112,6 +112,15 @@
   return param.un.setsig.ret;
 }
 
+int kz_sethandler(int signo, kz_handler handler)
+{
+  kz_syscall_param_t param;
+  param.un.sethandler.signo = signo;
+  param.un.sethandler.handler = handler;
+  kz_syscall(KZ_SYSCALL_TYPE_SETHANDLER, &param);
+  return param.un.sethandler.ret;
+}
+
 int kz_debug(int sockt)
 {
   kz_syscall_param_t param;
diff -ruN kozos29/syscall.h kozos30/syscall.h
--- kozos29/syscall.h	Mon Dec 17 21:53:06 2007
+++ kozos30/syscall.h	Mon Dec 17 22:11:23 2007
@@ -16,6 +16,7 @@
   KZ_SYSCALL_TYPE_TIMER,
   KZ_SYSCALL_TYPE_PENDING,
   KZ_SYSCALL_TYPE_SETSIG,
+  KZ_SYSCALL_TYPE_SETHANDLER,
   KZ_SYSCALL_TYPE_DEBUG,
   KZ_SYSCALL_TYPE_KMALLOC,
   KZ_SYSCALL_TYPE_KMFREE,
@@ -75,6 +76,11 @@
       int signo;
       int ret;
     } setsig;
+    struct {
+      int signo;
+      kz_handler handler;
+      int ret;
+    } sethandler;
     struct {
       int sockt;
       int ret;
diff -ruN kozos29/thread.c kozos30/thread.c
--- kozos29/thread.c	Mon Dec 17 21:53:06 2007
+++ kozos30/thread.c	Mon Dec 17 22:23:51 2007
@@ -28,9 +28,10 @@
 static unsigned int readyque_bitmap;
 static kz_timebuf *timers;
 static kz_thread *sigcalls[SIG_NUM];
+static kz_handler handlers[SIG_NUM];
 static int debug_sockt = 0;
 sigset_t block;
-static int on_os_stack = 0;
+static stack_t intrstack;
 
 kz_thread *current;
 
@@ -315,8 +316,17 @@
   return 0;
 }
 
+static int thread_sethandler(int signo, kz_handler handler)
+{
+  handlers[signo] = handler;
+  putcurrent();
+  return 0;
+}
+
 static void extintr_proc(int signo)
 {
+  if (handlers[signo])
+    handlers[signo](signo);
   if (sigcalls[signo])
     sendmsg(sigcalls[signo], 0, 0, NULL);
 }
@@ -401,6 +411,10 @@
   case KZ_SYSCALL_TYPE_SETSIG:
     p->un.setsig.ret = thread_setsig(p->un.setsig.signo);
     break;
+  case KZ_SYSCALL_TYPE_SETHANDLER:
+    p->un.sethandler.ret = thread_sethandler(p->un.sethandler.signo,
+					     p->un.sethandler.handler);
+    break;
   case KZ_SYSCALL_TYPE_DEBUG:
     p->un.debug.ret = thread_debug(p->un.debug.sockt);
     break;
@@ -496,19 +510,16 @@
    * これはOSの割り込み処理の再入になるが，以下の位置に限定して再入が行われる
    * ので問題は無い．
    */
-  on_os_stack = 1;
   sigprocmask(SIG_UNBLOCK, &block, NULL);
-  sigprocmask(SIG_BLOCK, &block, NULL);
-  on_os_stack = 0;
-
-  /* ここで SIGALRM が発生するとシグナルを取りこぼす．．．要検討 */
 
   setcontext(&current->context.uap);
 }
 
 static void thread_intr(int signo, siginfo_t *info, ucontext_t *uap)
 {
-  if (!on_os_stack) {
+  unsigned int esp = uap->uc_mcontext.mc_esp;
+  if ((esp <  (unsigned int)intrstack.ss_sp) ||
+      (esp >= (unsigned int)intrstack.ss_sp + intrstack.ss_size)) {
     memcpy(&current->context.uap, uap, sizeof(ucontext_t));
   }
   thread_intrvec(signo);
@@ -517,19 +528,19 @@
 static void thread_start(kz_func func, char *name, int pri, int argc, char *argv[])
 {
   struct sigaction sa;
-  stack_t sigstack;
 
   memset(threads, 0, sizeof(threads));
   memset(readyque, 0, sizeof(readyque));
   memset(sigcalls, 0, sizeof(sigcalls));
+  memset(handlers, 0, sizeof(handlers));
 
   readyque_bitmap = 0;
   timers = NULL;
 
-  sigstack.ss_sp = malloc(SIGSTKSZ);
-  sigstack.ss_size = SIGSTKSZ;
-  sigstack.ss_flags = 0;
-  sigaltstack(&sigstack, NULL);
+  intrstack.ss_sp = malloc(SIGSTKSZ);
+  intrstack.ss_size = SIGSTKSZ;
+  intrstack.ss_flags = 0;
+  sigaltstack(&intrstack, NULL);
 
   memset(&sa, 0, sizeof(sa));
   sa.sa_sigaction = (void (*)(int, siginfo_t *, void *))thread_intr;