diff --git a/arch/x86/kernel/include/signal.h b/arch/x86/kernel/include/signal.h
index 8de34ce6..23735056 100644
--- a/arch/x86/kernel/include/signal.h
+++ b/arch/x86/kernel/include/signal.h
@@ -33,31 +33,28 @@ struct sigaction {
 	sigset_t sa_mask;
 };
 
-//// work in progress
-struct sigbackup {
-	unsigned long rc; // return code of rt_sigreturn (rax)
-	void	*uctx;
-	sigset_t mask;
-	double	fpregs[16];
-	
-};
-////
+#define SA_NOCLDSTOP    0x00000001u
+#define SA_NOCLDWAIT    0x00000002u
+#define SA_NODEFER      0x40000000u
+#define SA_ONSTACK      0x08000000u
+#define SA_RESETHAND    0x80000000u
+#define SA_RESTART      0x10000000u
+#define SA_SIGINFO      0x00000004u
 
 struct k_sigaction {
         struct sigaction sa;
 };
 
-struct sigstack {
-	void	*ss_sp;
-	int	ss_onstack;
-};
-
 typedef struct sigaltstack {
 	void	*ss_sp;
 	int	ss_flags;
 	size_t	ss_size;
 } stack_t;
 
+#define MINSIGSTKSZ 2048
+#define SS_ONSTACK 1
+#define SS_DISABLE 2
+
 typedef union sigval {
 	int sival_int;
 	void *sival_ptr;
diff --git a/arch/x86/kernel/syscall.c b/arch/x86/kernel/syscall.c
index 2caad76e..21259603 100644
--- a/arch/x86/kernel/syscall.c
+++ b/arch/x86/kernel/syscall.c
@@ -121,6 +121,8 @@ fault:
 struct sigsp {
 	struct x86_regs regs;
 	unsigned long sigrc;
+	unsigned long sigmask;
+	int ssflags;
 };
 
 SYSCALL_DECLARE(rt_sigreturn)
@@ -133,8 +135,9 @@ SYSCALL_DECLARE(rt_sigreturn)
 	asm("movq %%gs:132, %0" : "=r" (regs));
 	--regs;
 
-	proc->sigmask.__val[0] = proc->supmask.__val[0];
 	sigsp = (struct sigsp *)regs->rsp;
+	proc->sigmask.__val[0] = sigsp->sigmask;
+	proc->sigstack.ss_flags = sigsp->ssflags;
 	if(copy_from_user(proc, regs, &sigsp->regs, sizeof(struct x86_regs)))
 		return rc;
 	copy_from_user(proc, &rc, &sigsp->sigrc, sizeof(long));
@@ -178,8 +181,20 @@ do_signal(unsigned long rc, void *regs0, struct process *proc, struct sig_pendin
 	else if(k->sa.sa_handler){
 		unsigned long *usp; /* user stack */
 		struct sigsp *sigsp;
+		int	ssflags = proc->sigstack.ss_flags;
+		unsigned long	mask = (unsigned long)proc->sigmask.__val[0];
 
-		usp = (unsigned long *)regs->rsp;
+		if((k->sa.sa_flags & SA_ONSTACK) &&
+		   !(proc->sigstack.ss_flags & SS_DISABLE) &&
+		   !(proc->sigstack.ss_flags & SS_ONSTACK)){
+			unsigned long lsp;
+			lsp = ((unsigned long)(((char *)proc->sigstack.ss_sp) + proc->sigstack.ss_size)) & 0xfffffffffffffff8UL;
+			usp = (unsigned long *)lsp;
+			proc->sigstack.ss_flags |= SS_ONSTACK;
+		}
+		else{
+			usp = (unsigned long *)regs->rsp;
+		}
 		sigsp = ((struct sigsp *)usp) - 1;
 		if(copy_to_user(proc, &sigsp->regs, regs, sizeof(struct x86_regs)) ||
 		   copy_to_user(proc, &sigsp->sigrc, &rc, sizeof(long))){
@@ -188,6 +203,8 @@ do_signal(unsigned long rc, void *regs0, struct process *proc, struct sig_pendin
 			terminate(0, sig, (ihk_mc_user_context_t *)regs->rsp);
 			return;
 		}
+		sigsp->sigmask = mask;
+		sigsp->ssflags = ssflags;
 
 		usp = (unsigned long *)sigsp;
 		usp--;
@@ -197,8 +214,8 @@ do_signal(unsigned long rc, void *regs0, struct process *proc, struct sig_pendin
 		regs->rip = (unsigned long)k->sa.sa_handler;
 		regs->rsp = (unsigned long)usp;
 
-		kfree(pending);
 		proc->sigmask.__val[0] |= pending->sigmask.__val[0];
+		kfree(pending);
 		ihk_mc_spinlock_unlock(&proc->sighandler->lock, irqstate);
 	}
 	else{
@@ -342,7 +359,7 @@ do_kill(int pid, int tid, int sig)
 	mask = __sigmask(sig);
 	pending = NULL;
 	rc = 0;
-	if(sig < 34){
+	if(sig < 33){ // SIGRTMIN - SIGRTMAX
 		list_for_each_entry(pending, head, list){
 			if(pending->sigmask.__val[0] == mask)
 				break;
diff --git a/kernel/include/process.h b/kernel/include/process.h
index 0f6e63c4..5bc99fea 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -173,7 +173,7 @@ struct process {
 	int tid;
 	volatile int sigevent;
 	sigset_t sigmask;
-	sigset_t supmask;
+	stack_t sigstack;
 	ihk_spinlock_t	sigpendinglock;
 	struct list_head sigpending;
 	struct sig_shared *sigshared;
diff --git a/kernel/process.c b/kernel/process.c
index 3a9a6314..89f17126 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -148,6 +148,10 @@ struct process *create_process(unsigned long user_pc)
 	ihk_mc_spinlock_init(&proc->sigpendinglock);
 	INIT_LIST_HEAD(&proc->sigpending);
 
+	proc->sigstack.ss_sp = NULL;
+	proc->sigstack.ss_flags = SS_DISABLE;
+	proc->sigstack.ss_size = 0;
+
 	ihk_mc_init_user_process(&proc->ctx, &proc->uctx,
 	                         ((char *)proc) + 
 							 KERNEL_STACK_NR_PAGES * PAGE_SIZE, user_pc, 0);
@@ -218,7 +222,11 @@ struct process *clone_process(struct process *org, unsigned long pc,
 	if (clone_flags & CLONE_VM) {
 		ihk_atomic_inc(&org->vm->refcount);
 		proc->vm = org->vm;
-		
+
+		proc->sigstack.ss_sp = NULL;
+		proc->sigstack.ss_flags = SS_DISABLE;
+		proc->sigstack.ss_size = 0;
+
 		proc->sighandler = org->sighandler;
 		ihk_atomic_inc(&org->sighandler->use);
 
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 5dd7b94c..f2ccc583 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -1424,7 +1424,6 @@ SYSCALL_DECLARE(rt_sigprocmask)
 			break;
 		}
 	}
-	proc->supmask = proc->sigmask;
 	ihk_mc_spinlock_unlock(&proc->sighandler->lock, flag);
 	return 0;
 fault:
@@ -1587,15 +1586,28 @@ SYSCALL_DECLARE(sigaltstack)
 	stack_t *oss = (stack_t *)ihk_mc_syscall_arg1(ctx);
 	stack_t	wss;
 
-	memset(&wss, '\0', sizeof wss);
 	if(oss)
-		if(copy_to_user(proc, oss, &wss, sizeof wss))
+		if(copy_to_user(proc, oss, &proc->sigstack, sizeof wss))
 			return -EFAULT;
-	if(ss)
+	if(ss){
 		if(copy_from_user(proc, &wss, ss, sizeof wss))
 			return -EFAULT;
+		if(wss.ss_flags != 0 && wss.ss_flags != SS_DISABLE)
+			return -EINVAL;
+		if(wss.ss_flags == SS_DISABLE){
+			proc->sigstack.ss_sp = NULL;
+			proc->sigstack.ss_flags = SS_DISABLE;
+			proc->sigstack.ss_size = 0;
+		}
+		else{
+			if(wss.ss_size < MINSIGSTKSZ)
+				return -ENOMEM;
 
-	return -EOPNOTSUPP;
+			memcpy(&proc->sigstack, &wss, sizeof wss);
+		}
+	}
+
+	return 0;
 }
 
 SYSCALL_DECLARE(madvise)