Simplification of the signal trampoline and other cleanups.

o  Remove unused defines from genassym.c that were needed
   by the trampoline.
o  Add load_gs_param function to support.s that catches
   a fault when %gs is loaded with an invalid descriptor.
   The function returns EFAULT in that case.
o  Remove struct trapframe from mcontext_t and replace it
   with the list of registers.
o  Modify sendsig and sigreturn accordingly.

This commit contains a patch by bde.

Reviewed by: luoqi, jdp

16 files changed, 152 insertions, 162 deletions

diff --git a/sys/amd64/amd64/genassym.c b/sys/amd64/amd64/genassym.c
index 8299177..b95a9a7 100644
--- a/sys/amd64/amd64/genassym.c
+++ b/sys/amd64/amd64/genassym.c
@@ -148,18 +148,8 @@ main()
 	printf("#define\tTF_EFLAGS %#x\n", OS(trapframe, tf_eflags));
 
 	printf("#define\tSIGF_HANDLER %#x\n", OS(sigframe, sf_ahu.sf_handler));
-	printf("#define\tSIGF_SIGRET %#x\n", OS(sigframe, sf_sigreturn));
-	printf("#define\tSIGF_SC %#x\n", OS(osigframe, sf_siginfo.si_sc));
 	printf("#define\tSIGF_UC %#x\n", OS(sigframe, sf_uc));
 
-	printf("#define\tSC_PS %#x\n", OS(osigcontext, sc_ps));
-	printf("#define\tSC_FS %#x\n", OS(osigcontext, sc_fs));
-	printf("#define\tSC_GS %#x\n", OS(osigcontext, sc_gs));
-
-	printf("#define\tUC_EFLAGS %#x\n",
-	    OS(__ucontext, uc_mcontext.mc_tf.tf_eflags));
-	printf("#define\tUC_GS %#x\n", OS(__ucontext, uc_mcontext.mc_gs));
-
 	printf("#define\tB_READ %#x\n", B_READ);
 	printf("#define\tENOENT %d\n", ENOENT);
 	printf("#define\tEFAULT %d\n", EFAULT);
diff --git a/sys/amd64/amd64/locore.S b/sys/amd64/amd64/locore.S
index e87c275..a1b6ff7 100644
--- a/sys/amd64/amd64/locore.S
+++ b/sys/amd64/amd64/locore.S
@@ -415,37 +415,14 @@ NON_GPROF_ENTRY(prepare_usermode)
  */
 NON_GPROF_ENTRY(sigcode)
 	call	SIGF_HANDLER(%esp)		/* call signal handler */
-	movl	SIGF_SIGRET(%esp),%eax		/* Get sigreturn cookie */
-	cmpl	$0x0ABCDEF0,%eax		/* New one? */
-	jne	3f
-/* New signalling code */
-	lea	SIGF_UC(%esp),%eax		/* get ucontext */
+	lea	SIGF_UC(%esp),%eax		/* get ucontext_t */
 	pushl	%eax
-	testl	$PSL_VM,UC_EFLAGS(%eax)
-	jne	1f
-	movl	UC_GS(%eax),%gs			/* restore %gs */
-1:
-	movl	$SYS_sigreturn,%eax
-	pushl	%eax				/* junk to fake return addr. */
-	int	$0x80				/* enter kernel with args */
-						/* on stack */
-2:
-	jmp	2b
-/* Old signalling code */
-3:
-	lea	SIGF_SC(%esp),%eax		/* get sigcontext */
-	pushl	%eax
-	testl	$PSL_VM,SC_PS(%eax)
-	jne	4f
-	movl	SC_GS(%eax),%gs			/* restore %gs */
-4:
 	movl	$SYS_osigreturn,%eax
 	pushl	%eax				/* junk to fake return addr. */
 	int	$0x80				/* enter kernel with args */
 						/* on stack */
-5:
-	jmp	5b
-
+1:
+	jmp	1b
 	ALIGN_TEXT
 _esigcode:
 
diff --git a/sys/amd64/amd64/locore.s b/sys/amd64/amd64/locore.s
index e87c275..a1b6ff7 100644
--- a/sys/amd64/amd64/locore.s
+++ b/sys/amd64/amd64/locore.s
@@ -415,37 +415,14 @@ NON_GPROF_ENTRY(prepare_usermode)
  */
 NON_GPROF_ENTRY(sigcode)
 	call	SIGF_HANDLER(%esp)		/* call signal handler */
-	movl	SIGF_SIGRET(%esp),%eax		/* Get sigreturn cookie */
-	cmpl	$0x0ABCDEF0,%eax		/* New one? */
-	jne	3f
-/* New signalling code */
-	lea	SIGF_UC(%esp),%eax		/* get ucontext */
+	lea	SIGF_UC(%esp),%eax		/* get ucontext_t */
 	pushl	%eax
-	testl	$PSL_VM,UC_EFLAGS(%eax)
-	jne	1f
-	movl	UC_GS(%eax),%gs			/* restore %gs */
-1:
-	movl	$SYS_sigreturn,%eax
-	pushl	%eax				/* junk to fake return addr. */
-	int	$0x80				/* enter kernel with args */
-						/* on stack */
-2:
-	jmp	2b
-/* Old signalling code */
-3:
-	lea	SIGF_SC(%esp),%eax		/* get sigcontext */
-	pushl	%eax
-	testl	$PSL_VM,SC_PS(%eax)
-	jne	4f
-	movl	SC_GS(%eax),%gs			/* restore %gs */
-4:
 	movl	$SYS_osigreturn,%eax
 	pushl	%eax				/* junk to fake return addr. */
 	int	$0x80				/* enter kernel with args */
 						/* on stack */
-5:
-	jmp	5b
-
+1:
+	jmp	1b
 	ALIGN_TEXT
 _esigcode:
 
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 1ef6fb0..a682098 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -599,6 +599,7 @@ osendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	regs->tf_ds = _udatasel;
 	regs->tf_es = _udatasel;
 	regs->tf_fs = _udatasel;
+	load_gs(_udatasel);
 	regs->tf_ss = _udatasel;
 }
 
@@ -631,8 +632,8 @@ sendsig(catcher, sig, mask, code)
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = psp->ps_sigstk;
 	sf.sf_uc.uc_mcontext.mc_onstack = onstack;
-	sf.sf_uc.uc_mcontext.mc_tf = *regs;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
+	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(struct trapframe));
 
 	/* Allocate and validate space for the signal handler context. */
         if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
@@ -702,12 +703,12 @@ sendsig(catcher, sig, mask, code)
 		struct vm86_kernel *vm86 = &p->p_addr->u_pcb.pcb_ext->ext_vm86;
 
 		sf.sf_uc.uc_mcontext.mc_gs = tf->tf_vm86_gs;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_fs = tf->tf_vm86_fs;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_es = tf->tf_vm86_es;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_ds = tf->tf_vm86_ds;
+		sf.sf_uc.uc_mcontext.mc_fs = tf->tf_vm86_fs;
+		sf.sf_uc.uc_mcontext.mc_es = tf->tf_vm86_es;
+		sf.sf_uc.uc_mcontext.mc_ds = tf->tf_vm86_ds;
 
 		if (vm86->vm86_has_vme == 0)
-			sf.sf_uc.uc_mcontext.mc_tf.tf_eflags =
+			sf.sf_uc.uc_mcontext.mc_eflags =
 			    (tf->tf_eflags & ~(PSL_VIF | PSL_VIP)) |
 			    (vm86->vm86_eflags & (PSL_VIF | PSL_VIP));
 
@@ -725,8 +726,6 @@ sendsig(catcher, sig, mask, code)
 		tf->tf_eflags &= ~(PSL_VM|PSL_NT|PSL_T|PSL_VIF|PSL_VIP);
 	}
 
-	sf.sf_sigreturn = 0x0ABCDEF0;
-
 	/*
 	 * Copy the sigframe out to the user's stack.
 	 */
@@ -744,6 +743,7 @@ sendsig(catcher, sig, mask, code)
 	regs->tf_ds = _udatasel;
 	regs->tf_es = _udatasel;
 	regs->tf_fs = _udatasel;
+	load_gs(_udatasel);
 	regs->tf_ss = _udatasel;
 }
 
@@ -767,21 +767,15 @@ osigreturn(p, uap)
 	} */ *uap;
 {
 	register struct osigcontext *scp;
-	register struct osigframe *fp;
 	register struct trapframe *regs = p->p_md.md_regs;
 	int eflags;
 
-	/*
-	 * (XXX old comment) regs->tf_esp points to the return address.
-	 * The user scp pointer is above that.
-	 * The return address is faked in the signal trampoline code
-	 * for consistency.
-	 */
+	if ((p->p_flag & P_NEWSIGSET) != 0)
+		return sigreturn(p, (struct sigreturn_args *)uap);
+
 	scp = uap->sigcntxp;
-	fp = (struct osigframe *)
-	     ((caddr_t)scp - offsetof(struct osigframe, sf_siginfo.si_sc));
 
-	if (useracc((caddr_t)fp, sizeof (struct osigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)scp, sizeof (struct osigcontext), B_WRITE) == 0)
 		return(EFAULT);
 
 	eflags = scp->sc_ps;
@@ -847,6 +841,10 @@ osigreturn(p, uap)
 		regs->tf_ds = scp->sc_ds;
 		regs->tf_es = scp->sc_es;
 		regs->tf_fs = scp->sc_fs;
+		if (load_gs_param(scp->sc_gs)) {
+			trapsignal(p, SIGBUS, T_SEGNPFLT);
+			return (EFAULT);
+		}
 	}
 
 	/* restore scratch registers */
@@ -860,9 +858,6 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (useracc((caddr_t)scp, sizeof (*scp), B_WRITE) == 0)
-		return(EINVAL);
-
 	if (scp->sc_onstack & 01)
 		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
 	else
@@ -888,9 +883,11 @@ sigreturn(p, uap)
 	ucontext_t *ucp;
 	int cs, eflags;
 
+	p->p_flag |= P_NEWSIGSET;
+
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
+	eflags = ucp->uc_mcontext.mc_eflags;
 
 	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
@@ -920,7 +917,7 @@ sigreturn(p, uap)
 			vm86->vm86_eflags = eflags;	/* save VIF, VIP */
 			eflags = (tf->tf_eflags & ~VM_USERCHANGE) |					    (eflags & VM_USERCHANGE) | PSL_VM;
 		}
-		*regs = ucp->uc_mcontext.mc_tf;
+		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(struct trapframe));
 		tf->tf_vm86_ds = tf->tf_ds;
 		tf->tf_vm86_es = tf->tf_es;
 		tf->tf_vm86_fs = tf->tf_fs;
@@ -952,14 +949,17 @@ sigreturn(p, uap)
 		 * hardware check for invalid selectors, excess privilege in
 		 * other selectors, invalid %eip's and invalid %esp's.
 		 */
-		cs = ucp->uc_mcontext.mc_tf.tf_cs;
+		cs = ucp->uc_mcontext.mc_cs;
 		if (!CS_SECURE(cs)) {
 			printf("sigreturn: cs = 0x%x\n", cs);
 			trapsignal(p, SIGBUS, T_PROTFLT);
 			return(EINVAL);
 		}
-
-		*regs = ucp->uc_mcontext.mc_tf;
+		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(struct trapframe));
+		if (load_gs_param(ucp->uc_mcontext.mc_gs)) {
+			trapsignal(p, SIGBUS, T_SEGNPFLT);
+			return (EFAULT);
+		}
 	}
 
 	if (ucp->uc_mcontext.mc_onstack & 1)
@@ -1033,10 +1033,10 @@ setregs(p, entry, stack, ps_strings)
 	regs->tf_ebx = ps_strings;
 
 	/* reset %gs as well */
-	pcb->pcb_gs = _udatasel;
-	if (pcb == curpcb) {
+	if (pcb == curpcb)
 		load_gs(_udatasel);
-	}
+	else
+		pcb->pcb_gs = _udatasel;
 
 	/*
 	 * Initialize the math emulator (if any) for the current process.
diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
index ae99af9..6a6e9fc 100644
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -1586,6 +1586,21 @@ ENTRY(load_cr4)
 	movl	%eax,%cr4
 	ret
 
+/* int load_gs_param(caddr_t gs) */
+ENTRY(load_gs_param)
+	movl	_curpcb,%ecx
+	movl	$load_gs_param_fault,PCB_ONFAULT(%ecx)
+	movl	4(%esp),%eax
+	movl	%eax,%gs
+	xor	%eax,%eax
+	movl	%eax,PCB_ONFAULT(%ecx)
+	ret
+load_gs_param_fault:
+	movl	_curpcb,%ecx
+	movl	$0,PCB_ONFAULT(%ecx)
+	movl	$EFAULT,%eax
+	ret
+
 /*****************************************************************************/
 /* setjump, longjump                                                         */
 /*****************************************************************************/
diff --git a/sys/amd64/amd64/support.s b/sys/amd64/amd64/support.s
index ae99af9..6a6e9fc 100644
--- a/sys/amd64/amd64/support.s
+++ b/sys/amd64/amd64/support.s
@@ -1586,6 +1586,21 @@ ENTRY(load_cr4)
 	movl	%eax,%cr4
 	ret
 
+/* int load_gs_param(caddr_t gs) */
+ENTRY(load_gs_param)
+	movl	_curpcb,%ecx
+	movl	$load_gs_param_fault,PCB_ONFAULT(%ecx)
+	movl	4(%esp),%eax
+	movl	%eax,%gs
+	xor	%eax,%eax
+	movl	%eax,PCB_ONFAULT(%ecx)
+	ret
+load_gs_param_fault:
+	movl	_curpcb,%ecx
+	movl	$0,PCB_ONFAULT(%ecx)
+	movl	$EFAULT,%eax
+	ret
+
 /*****************************************************************************/
 /* setjump, longjump                                                         */
 /*****************************************************************************/
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
index 755e1e7..d9a43fa 100644
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -91,6 +91,7 @@ int	i586_copyout __P((const void *kaddr, void *udaddr, size_t len));
 void	i686_pagezero __P((void *addr));
 int	is_physical_memory __P((vm_offset_t addr));
 u_long	kvtop __P((void *addr));
+int	load_gs_param __P((u_int sel));
 void	setidt __P((int idx, alias_for_inthand_t *func, int typ, int dpl,
 		    int selec));
 void	swi_vm __P((void));
diff --git a/sys/amd64/include/sigframe.h b/sys/amd64/include/sigframe.h
index ac64ddb..e7b47fa 100644
--- a/sys/amd64/include/sigframe.h
+++ b/sys/amd64/include/sigframe.h
@@ -86,9 +86,8 @@ struct sigframe {
 		__siginfohandler_t	*sf_action;
 		__sighandler_t		*sf_handler;
 	} sf_ahu;
-	register_t	sf_sigreturn;	/* sigreturn to use */
-	siginfo_t	sf_si;		/* = *sf_siginfo (SA_SIGINFO case) */
 	ucontext_t	sf_uc;		/* = *sf_ucontext */
+	siginfo_t	sf_si;		/* = *sf_siginfo (SA_SIGINFO case) */
 };
 
 #endif /* !_MACHINE_SIGFRAME_H_ */
diff --git a/sys/amd64/include/ucontext.h b/sys/amd64/include/ucontext.h
index 0d72716..6397a31 100644
--- a/sys/amd64/include/ucontext.h
+++ b/sys/amd64/include/ucontext.h
@@ -35,13 +35,30 @@
 
 typedef struct __mcontext {
 	/*
-	 * The first 3 fields must match the definition of
+	 * The first 20 fields must match the definition of
 	 * sigcontext. So that we can support sigcontext
 	 * and ucontext_t at the same time.
 	 */
 	int	mc_onstack;		/* XXX - sigcontext compat. */
 	int	mc_gs;
-	struct	trapframe mc_tf;
+	int	mc_fs;
+	int	mc_es;
+	int	mc_ds;
+	int	mc_edi;
+	int	mc_esi;
+	int	mc_ebp;
+	int	mc_isp;
+	int	mc_ebx;
+	int	mc_edx;
+	int	mc_ecx;
+	int	mc_eax;
+	int	mc_trapno;
+	int	mc_err;
+	int	mc_eip;
+	int	mc_cs;
+	int	mc_eflags;
+	int	mc_esp;			/* machine state */
+	int	mc_ss;
 
 	int	mc_fpregs[28];		/* env87 + fpacc87 + u_long */
 	int	__spare__[17];
diff --git a/sys/i386/i386/genassym.c b/sys/i386/i386/genassym.c
index 8299177..b95a9a7 100644
--- a/sys/i386/i386/genassym.c
+++ b/sys/i386/i386/genassym.c
@@ -148,18 +148,8 @@ main()
 	printf("#define\tTF_EFLAGS %#x\n", OS(trapframe, tf_eflags));
 
 	printf("#define\tSIGF_HANDLER %#x\n", OS(sigframe, sf_ahu.sf_handler));
-	printf("#define\tSIGF_SIGRET %#x\n", OS(sigframe, sf_sigreturn));
-	printf("#define\tSIGF_SC %#x\n", OS(osigframe, sf_siginfo.si_sc));
 	printf("#define\tSIGF_UC %#x\n", OS(sigframe, sf_uc));
 
-	printf("#define\tSC_PS %#x\n", OS(osigcontext, sc_ps));
-	printf("#define\tSC_FS %#x\n", OS(osigcontext, sc_fs));
-	printf("#define\tSC_GS %#x\n", OS(osigcontext, sc_gs));
-
-	printf("#define\tUC_EFLAGS %#x\n",
-	    OS(__ucontext, uc_mcontext.mc_tf.tf_eflags));
-	printf("#define\tUC_GS %#x\n", OS(__ucontext, uc_mcontext.mc_gs));
-
 	printf("#define\tB_READ %#x\n", B_READ);
 	printf("#define\tENOENT %d\n", ENOENT);
 	printf("#define\tEFAULT %d\n", EFAULT);
diff --git a/sys/i386/i386/locore.s b/sys/i386/i386/locore.s
index e87c275..a1b6ff7 100644
--- a/sys/i386/i386/locore.s
+++ b/sys/i386/i386/locore.s
@@ -415,37 +415,14 @@ NON_GPROF_ENTRY(prepare_usermode)
  */
 NON_GPROF_ENTRY(sigcode)
 	call	SIGF_HANDLER(%esp)		/* call signal handler */
-	movl	SIGF_SIGRET(%esp),%eax		/* Get sigreturn cookie */
-	cmpl	$0x0ABCDEF0,%eax		/* New one? */
-	jne	3f
-/* New signalling code */
-	lea	SIGF_UC(%esp),%eax		/* get ucontext */
+	lea	SIGF_UC(%esp),%eax		/* get ucontext_t */
 	pushl	%eax
-	testl	$PSL_VM,UC_EFLAGS(%eax)
-	jne	1f
-	movl	UC_GS(%eax),%gs			/* restore %gs */
-1:
-	movl	$SYS_sigreturn,%eax
-	pushl	%eax				/* junk to fake return addr. */
-	int	$0x80				/* enter kernel with args */
-						/* on stack */
-2:
-	jmp	2b
-/* Old signalling code */
-3:
-	lea	SIGF_SC(%esp),%eax		/* get sigcontext */
-	pushl	%eax
-	testl	$PSL_VM,SC_PS(%eax)
-	jne	4f
-	movl	SC_GS(%eax),%gs			/* restore %gs */
-4:
 	movl	$SYS_osigreturn,%eax
 	pushl	%eax				/* junk to fake return addr. */
 	int	$0x80				/* enter kernel with args */
 						/* on stack */
-5:
-	jmp	5b
-
+1:
+	jmp	1b
 	ALIGN_TEXT
 _esigcode:
 
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index 1ef6fb0..a682098 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -599,6 +599,7 @@ osendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	regs->tf_ds = _udatasel;
 	regs->tf_es = _udatasel;
 	regs->tf_fs = _udatasel;
+	load_gs(_udatasel);
 	regs->tf_ss = _udatasel;
 }
 
@@ -631,8 +632,8 @@ sendsig(catcher, sig, mask, code)
 	sf.sf_uc.uc_sigmask = *mask;
 	sf.sf_uc.uc_stack = psp->ps_sigstk;
 	sf.sf_uc.uc_mcontext.mc_onstack = onstack;
-	sf.sf_uc.uc_mcontext.mc_tf = *regs;
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
+	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(struct trapframe));
 
 	/* Allocate and validate space for the signal handler context. */
         if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
@@ -702,12 +703,12 @@ sendsig(catcher, sig, mask, code)
 		struct vm86_kernel *vm86 = &p->p_addr->u_pcb.pcb_ext->ext_vm86;
 
 		sf.sf_uc.uc_mcontext.mc_gs = tf->tf_vm86_gs;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_fs = tf->tf_vm86_fs;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_es = tf->tf_vm86_es;
-		sf.sf_uc.uc_mcontext.mc_tf.tf_ds = tf->tf_vm86_ds;
+		sf.sf_uc.uc_mcontext.mc_fs = tf->tf_vm86_fs;
+		sf.sf_uc.uc_mcontext.mc_es = tf->tf_vm86_es;
+		sf.sf_uc.uc_mcontext.mc_ds = tf->tf_vm86_ds;
 
 		if (vm86->vm86_has_vme == 0)
-			sf.sf_uc.uc_mcontext.mc_tf.tf_eflags =
+			sf.sf_uc.uc_mcontext.mc_eflags =
 			    (tf->tf_eflags & ~(PSL_VIF | PSL_VIP)) |
 			    (vm86->vm86_eflags & (PSL_VIF | PSL_VIP));
 
@@ -725,8 +726,6 @@ sendsig(catcher, sig, mask, code)
 		tf->tf_eflags &= ~(PSL_VM|PSL_NT|PSL_T|PSL_VIF|PSL_VIP);
 	}
 
-	sf.sf_sigreturn = 0x0ABCDEF0;
-
 	/*
 	 * Copy the sigframe out to the user's stack.
 	 */
@@ -744,6 +743,7 @@ sendsig(catcher, sig, mask, code)
 	regs->tf_ds = _udatasel;
 	regs->tf_es = _udatasel;
 	regs->tf_fs = _udatasel;
+	load_gs(_udatasel);
 	regs->tf_ss = _udatasel;
 }
 
@@ -767,21 +767,15 @@ osigreturn(p, uap)
 	} */ *uap;
 {
 	register struct osigcontext *scp;
-	register struct osigframe *fp;
 	register struct trapframe *regs = p->p_md.md_regs;
 	int eflags;
 
-	/*
-	 * (XXX old comment) regs->tf_esp points to the return address.
-	 * The user scp pointer is above that.
-	 * The return address is faked in the signal trampoline code
-	 * for consistency.
-	 */
+	if ((p->p_flag & P_NEWSIGSET) != 0)
+		return sigreturn(p, (struct sigreturn_args *)uap);
+
 	scp = uap->sigcntxp;
-	fp = (struct osigframe *)
-	     ((caddr_t)scp - offsetof(struct osigframe, sf_siginfo.si_sc));
 
-	if (useracc((caddr_t)fp, sizeof (struct osigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)scp, sizeof (struct osigcontext), B_WRITE) == 0)
 		return(EFAULT);
 
 	eflags = scp->sc_ps;
@@ -847,6 +841,10 @@ osigreturn(p, uap)
 		regs->tf_ds = scp->sc_ds;
 		regs->tf_es = scp->sc_es;
 		regs->tf_fs = scp->sc_fs;
+		if (load_gs_param(scp->sc_gs)) {
+			trapsignal(p, SIGBUS, T_SEGNPFLT);
+			return (EFAULT);
+		}
 	}
 
 	/* restore scratch registers */
@@ -860,9 +858,6 @@ osigreturn(p, uap)
 	regs->tf_ss = scp->sc_ss;
 	regs->tf_isp = scp->sc_isp;
 
-	if (useracc((caddr_t)scp, sizeof (*scp), B_WRITE) == 0)
-		return(EINVAL);
-
 	if (scp->sc_onstack & 01)
 		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
 	else
@@ -888,9 +883,11 @@ sigreturn(p, uap)
 	ucontext_t *ucp;
 	int cs, eflags;
 
+	p->p_flag |= P_NEWSIGSET;
+
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
+	eflags = ucp->uc_mcontext.mc_eflags;
 
 	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
@@ -920,7 +917,7 @@ sigreturn(p, uap)
 			vm86->vm86_eflags = eflags;	/* save VIF, VIP */
 			eflags = (tf->tf_eflags & ~VM_USERCHANGE) |					    (eflags & VM_USERCHANGE) | PSL_VM;
 		}
-		*regs = ucp->uc_mcontext.mc_tf;
+		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(struct trapframe));
 		tf->tf_vm86_ds = tf->tf_ds;
 		tf->tf_vm86_es = tf->tf_es;
 		tf->tf_vm86_fs = tf->tf_fs;
@@ -952,14 +949,17 @@ sigreturn(p, uap)
 		 * hardware check for invalid selectors, excess privilege in
 		 * other selectors, invalid %eip's and invalid %esp's.
 		 */
-		cs = ucp->uc_mcontext.mc_tf.tf_cs;
+		cs = ucp->uc_mcontext.mc_cs;
 		if (!CS_SECURE(cs)) {
 			printf("sigreturn: cs = 0x%x\n", cs);
 			trapsignal(p, SIGBUS, T_PROTFLT);
 			return(EINVAL);
 		}
-
-		*regs = ucp->uc_mcontext.mc_tf;
+		bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(struct trapframe));
+		if (load_gs_param(ucp->uc_mcontext.mc_gs)) {
+			trapsignal(p, SIGBUS, T_SEGNPFLT);
+			return (EFAULT);
+		}
 	}
 
 	if (ucp->uc_mcontext.mc_onstack & 1)
@@ -1033,10 +1033,10 @@ setregs(p, entry, stack, ps_strings)
 	regs->tf_ebx = ps_strings;
 
 	/* reset %gs as well */
-	pcb->pcb_gs = _udatasel;
-	if (pcb == curpcb) {
+	if (pcb == curpcb)
 		load_gs(_udatasel);
-	}
+	else
+		pcb->pcb_gs = _udatasel;
 
 	/*
 	 * Initialize the math emulator (if any) for the current process.
diff --git a/sys/i386/i386/support.s b/sys/i386/i386/support.s
index ae99af9..6a6e9fc 100644
--- a/sys/i386/i386/support.s
+++ b/sys/i386/i386/support.s
@@ -1586,6 +1586,21 @@ ENTRY(load_cr4)
 	movl	%eax,%cr4
 	ret
 
+/* int load_gs_param(caddr_t gs) */
+ENTRY(load_gs_param)
+	movl	_curpcb,%ecx
+	movl	$load_gs_param_fault,PCB_ONFAULT(%ecx)
+	movl	4(%esp),%eax
+	movl	%eax,%gs
+	xor	%eax,%eax
+	movl	%eax,PCB_ONFAULT(%ecx)
+	ret
+load_gs_param_fault:
+	movl	_curpcb,%ecx
+	movl	$0,PCB_ONFAULT(%ecx)
+	movl	$EFAULT,%eax
+	ret
+
 /*****************************************************************************/
 /* setjump, longjump                                                         */
 /*****************************************************************************/
diff --git a/sys/i386/include/md_var.h b/sys/i386/include/md_var.h
index 755e1e7..d9a43fa 100644
--- a/sys/i386/include/md_var.h
+++ b/sys/i386/include/md_var.h
@@ -91,6 +91,7 @@ int	i586_copyout __P((const void *kaddr, void *udaddr, size_t len));
 void	i686_pagezero __P((void *addr));
 int	is_physical_memory __P((vm_offset_t addr));
 u_long	kvtop __P((void *addr));
+int	load_gs_param __P((u_int sel));
 void	setidt __P((int idx, alias_for_inthand_t *func, int typ, int dpl,
 		    int selec));
 void	swi_vm __P((void));
diff --git a/sys/i386/include/sigframe.h b/sys/i386/include/sigframe.h
index ac64ddb..e7b47fa 100644
--- a/sys/i386/include/sigframe.h
+++ b/sys/i386/include/sigframe.h
@@ -86,9 +86,8 @@ struct sigframe {
 		__siginfohandler_t	*sf_action;
 		__sighandler_t		*sf_handler;
 	} sf_ahu;
-	register_t	sf_sigreturn;	/* sigreturn to use */
-	siginfo_t	sf_si;		/* = *sf_siginfo (SA_SIGINFO case) */
 	ucontext_t	sf_uc;		/* = *sf_ucontext */
+	siginfo_t	sf_si;		/* = *sf_siginfo (SA_SIGINFO case) */
 };
 
 #endif /* !_MACHINE_SIGFRAME_H_ */
diff --git a/sys/i386/include/ucontext.h b/sys/i386/include/ucontext.h
index 0d72716..6397a31 100644
--- a/sys/i386/include/ucontext.h
+++ b/sys/i386/include/ucontext.h
@@ -35,13 +35,30 @@
 
 typedef struct __mcontext {
 	/*
-	 * The first 3 fields must match the definition of
+	 * The first 20 fields must match the definition of
 	 * sigcontext. So that we can support sigcontext
 	 * and ucontext_t at the same time.
 	 */
 	int	mc_onstack;		/* XXX - sigcontext compat. */
 	int	mc_gs;
-	struct	trapframe mc_tf;
+	int	mc_fs;
+	int	mc_es;
+	int	mc_ds;
+	int	mc_edi;
+	int	mc_esi;
+	int	mc_ebp;
+	int	mc_isp;
+	int	mc_ebx;
+	int	mc_edx;
+	int	mc_ecx;
+	int	mc_eax;
+	int	mc_trapno;
+	int	mc_err;
+	int	mc_eip;
+	int	mc_cs;
+	int	mc_eflags;
+	int	mc_esp;			/* machine state */
+	int	mc_ss;
 
 	int	mc_fpregs[28];		/* env87 + fpacc87 + u_long */
 	int	__spare__[17];