diff --git a/sys/alpha/alpha/machdep.c b/sys/alpha/alpha/machdep.c
index f048bbbc483..9c3ace5ff70 100644
--- a/sys/alpha/alpha/machdep.c
+++ b/sys/alpha/alpha/machdep.c
@@ -1258,7 +1258,7 @@ osendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	int oonstack, fsize, rndfsize;
 
 	frame = p->p_md.md_tf;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(alpha_pal_rdusp());
 	fsize = sizeof ksi;
 	rndfsize = ((fsize + 15) / 16) * 16;
 
@@ -1273,7 +1273,9 @@ osendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sip = (osiginfo_t *)((caddr_t)p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - rndfsize);
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sip = (osiginfo_t *)(alpha_pal_rdusp() - rndfsize);
 
@@ -1294,7 +1296,7 @@ osendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	/*
 	 * Build the signal context to be used by sigreturn.
 	 */
-	ksi.si_sc.sc_onstack = oonstack;
+	ksi.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	SIG2OSIG(*mask, ksi.si_sc.sc_mask);
 	ksi.si_sc.sc_pc = frame->tf_regs[FRAME_PC];
 	ksi.si_sc.sc_ps = frame->tf_regs[FRAME_PS];
@@ -1358,14 +1360,16 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	}
 
 	frame = p->p_md.md_tf;
-	oonstack = (p->p_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
+	oonstack = sigonstack(alpha_pal_rdusp());
 	rndfsize = ((sizeof(sf) + 15) / 16) * 16;
 
 	/* save user context */
 	bzero(&sf, sizeof(struct sigframe));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
-	sf.sf_uc.uc_mcontext.mc_onstack = oonstack;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 
 	fill_regs(p, (struct reg *)sf.sf_uc.uc_mcontext.mc_regs);
 	sf.sf_uc.uc_mcontext.mc_regs[R_SP] = alpha_pal_rdusp();
@@ -1390,7 +1394,9 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)((caddr_t)p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - rndfsize);
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sfp = (struct sigframe *)(alpha_pal_rdusp() - rndfsize);
 
@@ -1503,6 +1509,8 @@ osigreturn(struct proc *p,
 	 */
 	if (ksc.sc_regs[R_ZERO] != 0xACEDBADE)		/* magic number */
 		return (EINVAL);
+
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	/*
 	 * Restore the user-supplied information
 	 */
@@ -1510,6 +1518,7 @@ osigreturn(struct proc *p,
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	/*
 	 * longjmp is still implemented by calling osigreturn. The new
@@ -1571,10 +1580,12 @@ sigreturn(struct proc *p,
 	p->p_md.md_tf->tf_regs[FRAME_PC] = uc.uc_mcontext.mc_regs[R_PC];
 	alpha_pal_wrusp(uc.uc_mcontext.mc_regs[R_SP]);
 
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (uc.uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = uc.uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/alpha/include/cpu.h b/sys/alpha/include/cpu.h
index a0be38fe0f5..3da213f66d1 100644
--- a/sys/alpha/include/cpu.h
+++ b/sys/alpha/include/cpu.h
@@ -52,6 +52,8 @@
 
 #include <machine/frame.h>
 
+#define	cpu_getstack(p)		(alpha_pal_rdusp())
+
 /*
  * Arguments to hardclock and gatherstats encapsulate the previous
  * machine state in an opaque clockframe.  One the Alpha, we use
diff --git a/sys/alpha/osf1/osf1_signal.c b/sys/alpha/osf1/osf1_signal.c
index 738b0a45d05..770ccf32d01 100644
--- a/sys/alpha/osf1/osf1_signal.c
+++ b/sys/alpha/osf1/osf1_signal.c
@@ -583,7 +583,7 @@ osf1_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	psp = p->p_sigacts;
 
 	frame = p->p_md.md_tf;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(alpha_pal_rdusp());
 	fsize = sizeof ksi;
 	rndfsize = ((fsize + 15) / 16) * 16;
 
@@ -618,7 +618,7 @@ osf1_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	/*
 	 * Build the signal context to be used by sigreturn.
 	 */
-	ksi.si_sc.sc_onstack = oonstack;
+	ksi.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	bsd_to_osf1_sigset(mask, &ksi.si_sc.sc_mask);
 	ksi.si_sc.sc_pc = frame->tf_regs[FRAME_PC];
 	ksi.si_sc.sc_ps = frame->tf_regs[FRAME_PS];
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 2e6416745bb..5c059291c6b 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -494,14 +494,16 @@ osendsig(catcher, sig, mask, code)
 	p = curproc;
 	psp = p->p_sigacts;
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Allocate and validate space for the signal handler context. */
 	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		fp = (struct osigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct osigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		fp = (struct osigframe *)regs->tf_esp - 1;
 
@@ -560,7 +562,7 @@ osendsig(catcher, sig, mask, code)
 	sf.sf_siginfo.si_sc.sc_isp = regs->tf_isp;
 
 	/* Build the signal context to be used by osigreturn(). */
-	sf.sf_siginfo.si_sc.sc_onstack = oonstack;
+	sf.sf_siginfo.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	SIG2OSIG(*mask, sf.sf_siginfo.si_sc.sc_mask);
 	sf.sf_siginfo.si_sc.sc_sp = regs->tf_esp;
 	sf.sf_siginfo.si_sc.sc_fp = regs->tf_ebp;
@@ -633,13 +635,15 @@ sendsig(catcher, sig, mask, code)
 		return;
 	}
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Save user context. */
 	bzero(&sf, sizeof(sf));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
-	sf.sf_uc.uc_mcontext.mc_onstack = oonstack;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(*regs));
 
@@ -648,7 +652,9 @@ sendsig(catcher, sig, mask, code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct sigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sfp = (struct sigframe *)regs->tf_esp - 1;
 
@@ -849,10 +855,13 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (scp->sc_onstack & 01)
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
+	if (scp->sc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
+
 	SIGSETOLD(p->p_sigmask, scp->sc_mask);
 	SIG_CANTMASK(p->p_sigmask);
 	regs->tf_ebp = scp->sc_fp;
@@ -958,10 +967,13 @@ sigreturn(p, uap)
 
 		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs));
 	}
+
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (ucp->uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/amd64/include/cpu.h b/sys/amd64/include/cpu.h
index 669af64c1b4..9293ba29b74 100644
--- a/sys/amd64/include/cpu.h
+++ b/sys/amd64/include/cpu.h
@@ -58,7 +58,8 @@
 
 #define	cpu_exec(p)	/* nothing */
 #define cpu_swapin(p)	/* nothing */
-#define cpu_setstack(p, ap)		((p)->p_md.md_regs[SP] = (ap))
+#define	cpu_getstack(p)			((p)->p_md.md_regs->tf_esp)
+#define cpu_setstack(p, ap)		((p)->p_md.md_regs->tf_esp = (ap))
 
 #define	CLKF_USERMODE(framep) \
 	((ISPL((framep)->cf_cs) == SEL_UPL) || (framep->cf_eflags & PSL_VM))
diff --git a/sys/compat/svr4/svr4_signal.c b/sys/compat/svr4/svr4_signal.c
index c80538edb42..84f8ce07725 100644
--- a/sys/compat/svr4/svr4_signal.c
+++ b/sys/compat/svr4/svr4_signal.c
@@ -628,7 +628,7 @@ svr4_sys_context(p, uap)
 	case 0:
 		DPRINTF(("getcontext(%p)\n", uap->uc));
 		svr4_getcontext(p, &uc, &p->p_sigmask,
-		    p->p_sigstk.ss_flags & SS_ONSTACK);
+		    sigonstack(cpu_getstack(p)));
 		return copyout(&uc, uap->uc, sizeof(uc));
 
 	case 1: 
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index 2e6416745bb..5c059291c6b 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -494,14 +494,16 @@ osendsig(catcher, sig, mask, code)
 	p = curproc;
 	psp = p->p_sigacts;
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Allocate and validate space for the signal handler context. */
 	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		fp = (struct osigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct osigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		fp = (struct osigframe *)regs->tf_esp - 1;
 
@@ -560,7 +562,7 @@ osendsig(catcher, sig, mask, code)
 	sf.sf_siginfo.si_sc.sc_isp = regs->tf_isp;
 
 	/* Build the signal context to be used by osigreturn(). */
-	sf.sf_siginfo.si_sc.sc_onstack = oonstack;
+	sf.sf_siginfo.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	SIG2OSIG(*mask, sf.sf_siginfo.si_sc.sc_mask);
 	sf.sf_siginfo.si_sc.sc_sp = regs->tf_esp;
 	sf.sf_siginfo.si_sc.sc_fp = regs->tf_ebp;
@@ -633,13 +635,15 @@ sendsig(catcher, sig, mask, code)
 		return;
 	}
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Save user context. */
 	bzero(&sf, sizeof(sf));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
-	sf.sf_uc.uc_mcontext.mc_onstack = oonstack;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(*regs));
 
@@ -648,7 +652,9 @@ sendsig(catcher, sig, mask, code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct sigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sfp = (struct sigframe *)regs->tf_esp - 1;
 
@@ -849,10 +855,13 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (scp->sc_onstack & 01)
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
+	if (scp->sc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
+
 	SIGSETOLD(p->p_sigmask, scp->sc_mask);
 	SIG_CANTMASK(p->p_sigmask);
 	regs->tf_ebp = scp->sc_fp;
@@ -958,10 +967,13 @@ sigreturn(p, uap)
 
 		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs));
 	}
+
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (ucp->uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/i386/include/cpu.h b/sys/i386/include/cpu.h
index 669af64c1b4..9293ba29b74 100644
--- a/sys/i386/include/cpu.h
+++ b/sys/i386/include/cpu.h
@@ -58,7 +58,8 @@
 
 #define	cpu_exec(p)	/* nothing */
 #define cpu_swapin(p)	/* nothing */
-#define cpu_setstack(p, ap)		((p)->p_md.md_regs[SP] = (ap))
+#define	cpu_getstack(p)			((p)->p_md.md_regs->tf_esp)
+#define cpu_setstack(p, ap)		((p)->p_md.md_regs->tf_esp = (ap))
 
 #define	CLKF_USERMODE(framep) \
 	((ISPL((framep)->cf_cs) == SEL_UPL) || (framep->cf_eflags & PSL_VM))
diff --git a/sys/i386/linux/linux.h b/sys/i386/linux/linux.h
index d253897cd94..8aff68a2ec9 100644
--- a/sys/i386/linux/linux.h
+++ b/sys/i386/linux/linux.h
@@ -163,7 +163,6 @@ struct linux_new_utsname {
 
 /* sigaltstack */
 #define LINUX_MINSIGSTKSZ	2048
-#define LINUX_SS_ONSTACK_BC	0 	/* backwards compat SS_ONSTACK */
 #define LINUX_SS_ONSTACK	1
 #define LINUX_SS_DISABLE	2
 
diff --git a/sys/i386/linux/linux_machdep.c b/sys/i386/linux/linux_machdep.c
index c152a108d2b..7e4b37e4b32 100644
--- a/sys/i386/linux/linux_machdep.c
+++ b/sys/i386/linux/linux_machdep.c
@@ -82,8 +82,6 @@ linux_to_bsd_sigaltstack(int lsa)
 		bsa |= SS_DISABLE;
 	if (lsa & LINUX_SS_ONSTACK)
 		bsa |= SS_ONSTACK;
-	if (lsa == LINUX_SS_ONSTACK_BC)
-		bsa = SS_ONSTACK;
 	return (bsa);
 }
 
diff --git a/sys/i386/linux/linux_sysvec.c b/sys/i386/linux/linux_sysvec.c
index 7d7fccbdfc2..cd944a2a488 100644
--- a/sys/i386/linux/linux_sysvec.c
+++ b/sys/i386/linux/linux_sysvec.c
@@ -205,7 +205,7 @@ linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	int oonstack;
 
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 #ifdef DEBUG
 	printf("Linux-emul(%ld): linux_rt_sendsig(%p, %d, %p, %lu)\n",
@@ -218,10 +218,8 @@ linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	    SIGISMEMBER(p->p_sigacts->ps_sigonstack, sig)) {
 		fp = (struct linux_rt_sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct linux_rt_sigframe));
-		p->p_sigstk.ss_flags |= SS_ONSTACK;
-	} else {
+	} else
 		fp = (struct linux_rt_sigframe *)regs->tf_esp - 1;
-	}
 
 	/*
 	 * grow() will return FALSE if the fp will not fit inside the stack
@@ -240,8 +238,8 @@ linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 		SIGDELSET(p->p_sigcatch, SIGILL);
 		SIGDELSET(p->p_sigmask, SIGILL);
 #ifdef DEBUG
-		printf("Linux-emul(%ld): linux_rt_sendsig -- bad stack %p, SS_ONSTACK: 0x%x ",
-	    (long)p->p_pid, fp, p->p_sigstk.ss_flags & SS_ONSTACK);
+		printf("Linux-emul(%ld): linux_rt_sendsig -- bad stack %p, "
+		    "oonstack=%x\n", (long)p->p_pid, fp, oonstack);
 #endif
 		psignal(p, SIGILL);
 		return;
@@ -271,9 +269,9 @@ linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	frame.sf_sc.uc_link = NULL;		/* XXX ??? */
 
 	frame.sf_sc.uc_stack.ss_sp = p->p_sigstk.ss_sp;
-	frame.sf_sc.uc_stack.ss_flags =
-	    bsd_to_linux_sigaltstack(p->p_sigstk.ss_flags);
 	frame.sf_sc.uc_stack.ss_size = p->p_sigstk.ss_size;
+	frame.sf_sc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? LINUX_SS_ONSTACK : 0) : LINUX_SS_DISABLE;
 
 	bsd_to_linux_sigset(mask, &frame.sf_sc.uc_sigmask);
 
@@ -298,9 +296,10 @@ linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	frame.sf_sc.uc_mcontext.sc_trapno = code;	/* XXX ???? */
 
 #ifdef DEBUG
-	printf("Linux-emul(%ld): rt_sendsig flags: 0x%x, sp: %p, ss: 0x%x, mask: 0x%x\n",
-	    (long)p->p_pid, frame.sf_sc.uc_stack.ss_flags,  p->p_sigstk.ss_sp, 
-	    p->p_sigstk.ss_size, frame.sf_sc.uc_mcontext.sc_mask);
+	printf("Linux-emul(%ld): rt_sendsig flags: 0x%x, sp: %p, ss: 0x%x, "
+	    "mask: 0x%x\n", (long)p->p_pid, frame.sf_sc.uc_stack.ss_flags,
+	    p->p_sigstk.ss_sp, p->p_sigstk.ss_size,
+	    frame.sf_sc.uc_mcontext.sc_mask);
 #endif
 
 	if (copyout(&frame, fp, sizeof(frame)) != 0) {
@@ -355,7 +354,7 @@ linux_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	}
 
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 #ifdef DEBUG
 	printf("Linux-emul(%ld): linux_sendsig(%p, %d, %p, %lu)\n",
@@ -369,10 +368,8 @@ linux_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	    SIGISMEMBER(p->p_sigacts->ps_sigonstack, sig)) {
 		fp = (struct linux_sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct linux_sigframe));
-		p->p_sigstk.ss_flags |= SS_ONSTACK;
-	} else {
+	} else
 		fp = (struct linux_sigframe *)regs->tf_esp - 1;
-	}
 
 	/*
 	 * grow() will return FALSE if the fp will not fit inside the stack
@@ -521,7 +518,6 @@ linux_sigreturn(p, args)
 		return(EINVAL);
 	}
 
-	p->p_sigstk.ss_flags &= ~SS_ONSTACK;
 	lmask.__bits[0] = frame.sf_sc.sc_mask;
 	for (i = 0; i < (LINUX_NSIG_WORDS-1); i++)
 		lmask.__bits[i+1] = frame.sf_extramask[i];
@@ -621,7 +617,6 @@ linux_rt_sigreturn(p, args)
 		return(EINVAL);
 	}
 
-	p->p_sigstk.ss_flags &= ~SS_ONSTACK;
 	linux_to_bsd_sigset(&uc.uc_sigmask, &p->p_sigmask);
 	SIG_CANTMASK(p->p_sigmask);
 
diff --git a/sys/i386/svr4/svr4_machdep.c b/sys/i386/svr4/svr4_machdep.c
index 38c5cc8fb50..018fb74d3b0 100644
--- a/sys/i386/svr4/svr4_machdep.c
+++ b/sys/i386/svr4/svr4_machdep.c
@@ -404,7 +404,7 @@ svr4_sendsig(catcher, sig, mask, code)
 #endif
 
 	tf = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(tf->tf_esp);
 
 	/*
 	 * Allocate space for the signal handler context.
diff --git a/sys/ia64/ia64/machdep.c b/sys/ia64/ia64/machdep.c
index bed49d53010..bc0ae1becb4 100644
--- a/sys/ia64/ia64/machdep.c
+++ b/sys/ia64/ia64/machdep.c
@@ -785,7 +785,7 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	int oonstack, rndfsize;
 
 	frame = p->p_md.md_tf;
-	oonstack = (p->p_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
+	oonstack = sigonstack(frame->tf_r[FRAME_SP]);
 	rndfsize = ((sizeof(sf) + 15) / 16) * 16;
 
 	/*
@@ -798,7 +798,10 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	bzero(&sf, sizeof(struct sigframe));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
 	sf.sf_uc.uc_mcontext.mc_flags = IA64_MC_FLAG_ONSTACK;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 
 	sf.sf_uc.uc_mcontext.mc_nat     = 0; /* XXX */
 	sf.sf_uc.uc_mcontext.mc_sp	= frame->tf_r[FRAME_SP];
@@ -837,8 +840,9 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 		sbs = (u_int64_t) p->p_sigstk.ss_sp;
 		sfp = (struct sigframe *)((caddr_t)p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - rndfsize);
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
-		sf.sf_uc.uc_mcontext.mc_onstack |= 1;
+#endif
 	} else
 		sfp = (struct sigframe *)(frame->tf_r[FRAME_SP] - rndfsize);
 
@@ -1009,10 +1013,12 @@ sigreturn(struct proc *p,
 
 	frame->tf_r[FRAME_SP] = mcp->mc_sp;
 
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (uc.uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = uc.uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/ia64/include/cpu.h b/sys/ia64/include/cpu.h
index c6ebd1c6145..d581447357a 100644
--- a/sys/ia64/include/cpu.h
+++ b/sys/ia64/include/cpu.h
@@ -52,6 +52,8 @@
 
 #include <machine/frame.h>
 
+#define	cpu_getstack(p)		((p)->p_md.md_tf->tf_r[FRAME_SP])
+
 /*
  * Arguments to hardclock and gatherstats encapsulate the previous
  * machine state in an opaque clockframe.  One the Alpha, we use
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 345bc31e49d..434420beab2 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -782,20 +782,25 @@ osigstack(p, uap)
 	register struct osigstack_args *uap;
 {
 	struct sigstack ss;
-	int error = 0;
+	int error;
 
-	ss.ss_sp = p->p_sigstk.ss_sp;
-	ss.ss_onstack = p->p_sigstk.ss_flags & SS_ONSTACK;
-	if (uap->oss && (error = copyout(&ss, uap->oss,
-	    sizeof(struct sigstack))))
-		return (error);
-	if (uap->nss && (error = copyin(uap->nss, &ss, sizeof(ss))) == 0) {
+	if (uap->oss != NULL) {
+		ss.ss_sp = p->p_sigstk.ss_sp;
+		ss.ss_onstack = sigonstack(cpu_getstack(p));
+		error = copyout(&ss, uap->oss, sizeof(struct sigstack));
+		if (error)
+			return (error);
+	}
+
+	if (uap->nss != NULL) {
+		if ((error = copyin(uap->nss, &ss, sizeof(ss))) != 0)
+			return (error);
 		p->p_sigstk.ss_sp = ss.ss_sp;
 		p->p_sigstk.ss_size = 0;
 		p->p_sigstk.ss_flags |= ss.ss_onstack & SS_ONSTACK;
 		p->p_flag |= P_ALTSTACK;
 	}
-	return (error);
+	return (0);
 }
 #endif /* COMPAT_43 || COMPAT_SUNOS */
 
@@ -812,28 +817,33 @@ sigaltstack(p, uap)
 	register struct sigaltstack_args *uap;
 {
 	stack_t ss;
-	int error;
+	int error, oonstack;
 
-	if ((p->p_flag & P_ALTSTACK) == 0)
-		p->p_sigstk.ss_flags |= SS_DISABLE;
-	if (uap->oss && (error = copyout(&p->p_sigstk, uap->oss,
-	    sizeof(stack_t))))
-		return (error);
-	if (uap->ss == 0)
-		return (0);
-	if ((error = copyin(uap->ss, &ss, sizeof(ss))))
-		return (error);
-	if (ss.ss_flags & SS_DISABLE) {
-		if (p->p_sigstk.ss_flags & SS_ONSTACK)
-			return (EINVAL);
-		p->p_flag &= ~P_ALTSTACK;
-		p->p_sigstk.ss_flags = ss.ss_flags;
-		return (0);
+	oonstack = sigonstack(cpu_getstack(p));
+
+	if (uap->oss != NULL) {
+		ss = p->p_sigstk;
+		ss.ss_flags = (p->p_flag & P_ALTSTACK)
+		    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+		if ((error = copyout(&ss, uap->oss, sizeof(stack_t))) != 0)
+			return (error);
+	}
+
+	if (uap->ss != NULL) {
+		if (oonstack)
+			return (EPERM);
+		if ((error = copyin(uap->ss, &ss, sizeof(ss))) != 0)
+			return (error);
+		if ((ss.ss_flags & ~SS_DISABLE) != 0)
+			return (EINVAL);
+		if (!(ss.ss_flags & SS_DISABLE)) {
+			if (ss.ss_size < p->p_sysent->sv_minsigstksz)
+				return (ENOMEM);
+			p->p_sigstk = ss;
+			p->p_flag |= P_ALTSTACK;
+		} else
+			p->p_flag &= ~P_ALTSTACK;
 	}
-	if (ss.ss_size < p->p_sysent->sv_minsigstksz)
-		return (ENOMEM);
-	p->p_flag |= P_ALTSTACK;
-	p->p_sigstk = ss;
 	return (0);
 }
 
diff --git a/sys/pc98/i386/machdep.c b/sys/pc98/i386/machdep.c
index 0320ad0fa07..a7567492aab 100644
--- a/sys/pc98/i386/machdep.c
+++ b/sys/pc98/i386/machdep.c
@@ -495,14 +495,16 @@ osendsig(catcher, sig, mask, code)
 	p = curproc;
 	psp = p->p_sigacts;
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Allocate and validate space for the signal handler context. */
 	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		fp = (struct osigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct osigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		fp = (struct osigframe *)regs->tf_esp - 1;
 
@@ -561,7 +563,7 @@ osendsig(catcher, sig, mask, code)
 	sf.sf_siginfo.si_sc.sc_isp = regs->tf_isp;
 
 	/* Build the signal context to be used by osigreturn(). */
-	sf.sf_siginfo.si_sc.sc_onstack = oonstack;
+	sf.sf_siginfo.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	SIG2OSIG(*mask, sf.sf_siginfo.si_sc.sc_mask);
 	sf.sf_siginfo.si_sc.sc_sp = regs->tf_esp;
 	sf.sf_siginfo.si_sc.sc_fp = regs->tf_ebp;
@@ -634,13 +636,15 @@ sendsig(catcher, sig, mask, code)
 		return;
 	}
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Save user context. */
 	bzero(&sf, sizeof(sf));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
-	sf.sf_uc.uc_mcontext.mc_onstack = oonstack;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(*regs));
 
@@ -649,7 +653,9 @@ sendsig(catcher, sig, mask, code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct sigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sfp = (struct sigframe *)regs->tf_esp - 1;
 
@@ -850,10 +856,13 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (scp->sc_onstack & 01)
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
+	if (scp->sc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
+
 	SIGSETOLD(p->p_sigmask, scp->sc_mask);
 	SIG_CANTMASK(p->p_sigmask);
 	regs->tf_ebp = scp->sc_fp;
@@ -959,10 +968,13 @@ sigreturn(p, uap)
 
 		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs));
 	}
+
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (ucp->uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/pc98/pc98/machdep.c b/sys/pc98/pc98/machdep.c
index 0320ad0fa07..a7567492aab 100644
--- a/sys/pc98/pc98/machdep.c
+++ b/sys/pc98/pc98/machdep.c
@@ -495,14 +495,16 @@ osendsig(catcher, sig, mask, code)
 	p = curproc;
 	psp = p->p_sigacts;
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Allocate and validate space for the signal handler context. */
 	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		fp = (struct osigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct osigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		fp = (struct osigframe *)regs->tf_esp - 1;
 
@@ -561,7 +563,7 @@ osendsig(catcher, sig, mask, code)
 	sf.sf_siginfo.si_sc.sc_isp = regs->tf_isp;
 
 	/* Build the signal context to be used by osigreturn(). */
-	sf.sf_siginfo.si_sc.sc_onstack = oonstack;
+	sf.sf_siginfo.si_sc.sc_onstack = (oonstack) ? 1 : 0;
 	SIG2OSIG(*mask, sf.sf_siginfo.si_sc.sc_mask);
 	sf.sf_siginfo.si_sc.sc_sp = regs->tf_esp;
 	sf.sf_siginfo.si_sc.sc_fp = regs->tf_ebp;
@@ -634,13 +636,15 @@ sendsig(catcher, sig, mask, code)
 		return;
 	}
 	regs = p->p_md.md_regs;
-	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;
+	oonstack = sigonstack(regs->tf_esp);
 
 	/* Save user context. */
 	bzero(&sf, sizeof(sf));
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = p->p_sigstk;
-	sf.sf_uc.uc_mcontext.mc_onstack = oonstack;
+	sf.sf_uc.uc_stack.ss_flags = (p->p_flag & P_ALTSTACK)
+	    ? ((oonstack) ? SS_ONSTACK : 0) : SS_DISABLE;
+	sf.sf_uc.uc_mcontext.mc_onstack = (oonstack) ? 1 : 0;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(*regs));
 
@@ -649,7 +653,9 @@ sendsig(catcher, sig, mask, code)
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(p->p_sigstk.ss_sp +
 		    p->p_sigstk.ss_size - sizeof(struct sigframe));
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
+#endif
 	} else
 		sfp = (struct sigframe *)regs->tf_esp - 1;
 
@@ -850,10 +856,13 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (scp->sc_onstack & 01)
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
+	if (scp->sc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
+
 	SIGSETOLD(p->p_sigmask, scp->sc_mask);
 	SIG_CANTMASK(p->p_sigmask);
 	regs->tf_ebp = scp->sc_fp;
@@ -959,10 +968,13 @@ sigreturn(p, uap)
 
 		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs));
 	}
+
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	if (ucp->uc_mcontext.mc_onstack & 1)
 		p->p_sigstk.ss_flags |= SS_ONSTACK;
 	else
 		p->p_sigstk.ss_flags &= ~SS_ONSTACK;
+#endif
 
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 67d525ca0fb..f52b2d2e653 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -395,6 +395,20 @@ MALLOC_DECLARE(M_ZOMBIE);
 MALLOC_DECLARE(M_PARGS);
 #endif
 
+static __inline int
+sigonstack(size_t sp)
+{
+	register struct proc *p = curproc;
+
+	return ((p->p_flag & P_ALTSTACK) ?
+#if defined(COMPAT_43) || defined(COMPAT_SUNOS)
+	    ((p->p_sigstk.ss_size == 0) ? (p->p_sigstk.ss_flags & SS_ONSTACK) :
+		((sp - (size_t)p->p_sigstk.ss_sp) < p->p_sigstk.ss_size))
+#else
+	    ((sp - (size_t)p->p_sigstk.ss_sp) < p->p_sigstk.ss_size)
+#endif
+	    : 0);
+}
 
 /* Handy macro to determine of p1 can mangle p2 */