Re-introduction of sigcontext.

struct sigcontext and ucontext_t/mcontext_t are defined in such
a way that both (ie struct sigcontext and ucontext_t) can be
passed on to sigreturn. The signal handler is still given a
ucontext_t for maximum flexibility.

For backward compatibility sigreturn restores the state for the
alternate signal stack from sigcontext.sc_onstack and not from
ucontext_t.uc_stack. A good way to determine which value the
application has set and thus which value to use, is still open
for discussion.

NOTE: This change should only affect those binaries that use
      sigcontext and/or ucontext_t. In the source tree itself
      this is only doscmd. Recompilation is required for those
      applications.

This commit also fixes a lot of style bugs without hopefully
adding new ones.

NOTE: struct sigaltstack.ss_size now has type size_t again. For
      some reason I changed that into unsigned int.

Parts submitted by: bde
sigaltstack bug found by: bde

17 files changed, 390 insertions, 218 deletions

diff --git a/sys/alpha/alpha/machdep.c b/sys/alpha/alpha/machdep.c
index 85262fe2fdc1..ce72dcef6043 100644
--- a/sys/alpha/alpha/machdep.c
+++ b/sys/alpha/alpha/machdep.c
@@ -1269,7 +1269,7 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	struct trapframe *frame;
 	struct sigacts *psp;
 	struct sigframe sf, *sfp;
-	int rndfsize;
+	int onstack, rndfsize;
 
 	p = curproc;
 
@@ -1280,13 +1280,26 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 
 	frame = p->p_md.md_tf;
 	psp = p->p_sigacts;
+	onstack = (psp->ps_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
 	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 = psp->ps_sigstk;
-	sf.sf_uc.uc_mcontext.mc_tf = *frame;
+	sf.sf_uc.uc_mcontext.mc_onstack = onstack;
+
+	fill_regs(p, (struct reg *)sf.sf_uc.uc_mcontext.mc_regs);
+	sf.sf_uc.uc_mcontext.mc_regs[R_SP] = alpha_pal_rdusp();
+	sf.sf_uc.uc_mcontext.mc_regs[R_ZERO] = 0xACEDBADE;   /* magic number */
+	sf.sf_uc.uc_mcontext.mc_regs[R_PS] = frame->tf_regs[FRAME_PS];
+	sf.sf_uc.uc_mcontext.mc_regs[R_PC] = frame->tf_regs[FRAME_PC];
+	sf.sf_uc.uc_mcontext.mc_regs[R_TRAPARG_A0] =
+	    frame->tf_regs[FRAME_TRAPARG_A0];
+	sf.sf_uc.uc_mcontext.mc_regs[R_TRAPARG_A1] =
+	    frame->tf_regs[FRAME_TRAPARG_A1];
+	sf.sf_uc.uc_mcontext.mc_regs[R_TRAPARG_A2] =
+	    frame->tf_regs[FRAME_TRAPARG_A2];
 
 	/*
 	 * Allocate and validate space for the signal handler
@@ -1295,8 +1308,7 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	 * will fail if the process has not already allocated
 	 * the space with a `brk'.
 	 */
-	if ((psp->ps_flags & SAS_ALTSTACK) != 0 &&
-	    (psp->ps_sigstk.ss_flags & SS_ONSTACK) == 0 &&
+	if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)((caddr_t)psp->ps_sigstk.ss_sp +
 		    psp->ps_sigstk.ss_size - rndfsize);
@@ -1328,8 +1340,6 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 		return;
 	}
 
-	sf.sf_uc.uc_mcontext.mc_tf.tf_regs[FRAME_SP] = alpha_pal_rdusp();
-
 	/* save the floating-point state, if necessary, then copy it. */
 	if (p == fpcurproc) {
 		alpha_pal_wrfen(1);
@@ -1418,6 +1428,10 @@ osigreturn(struct proc *p,
 	    copyin((caddr_t)scp, (caddr_t)&ksc, sizeof ksc))
 		return (EINVAL);
 
+	/*
+	 * XXX - Should we do this. What if we get a "handcrafted"
+	 * but valid sigcontext that hasn't the magic number?
+	 */
 	if (ksc.sc_regs[R_ZERO] != 0xACEDBADE)		/* magic number */
 		return (EINVAL);
 	/*
@@ -1464,6 +1478,7 @@ sigreturn(struct proc *p,
 {
 	ucontext_t uc, *ucp;
 	struct pcb *pcb;
+	unsigned long val;
 
 	ucp = uap->sigcntxp;
 
@@ -1491,13 +1506,18 @@ sigreturn(struct proc *p,
 	/*
 	 * Restore the user-supplied information
 	 */
-	*p->p_md.md_tf = uc.uc_mcontext.mc_tf;
-	p->p_md.md_tf->tf_regs[FRAME_PS] |= ALPHA_PSL_USERSET;
-	p->p_md.md_tf->tf_regs[FRAME_PS] &= ~ALPHA_PSL_USERCLR;
-	pcb->pcb_hw.apcb_usp = p->p_md.md_tf->tf_regs[FRAME_SP];
-	alpha_pal_wrusp(pcb->pcb_hw.apcb_usp);
+	set_regs(p, (struct reg *)uc.uc_mcontext.mc_regs);
+	val = (uc.uc_mcontext.mc_regs[R_PS] | ALPHA_PSL_USERSET) &
+	    ~ALPHA_PSL_USERCLR;
+	p->p_md.md_tf->tf_regs[FRAME_PS] = val;
+	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 (uc.uc_mcontext.mc_onstack & 1)
+		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
+	else
+		p->p_sigacts->ps_sigstk.ss_flags &= ~SS_ONSTACK;
 
-	p->p_sigacts->ps_sigstk = uc.uc_stack;
 	p->p_sigmask = uc.uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
 
diff --git a/sys/alpha/include/reg.h b/sys/alpha/include/reg.h
index 341a39659178..879aeed1e8c6 100644
--- a/sys/alpha/include/reg.h
+++ b/sys/alpha/include/reg.h
@@ -73,6 +73,15 @@
 #define	R_SP	30
 #define	R_ZERO	31
 
+/*
+ * Register extensions used in mcontext_t
+ */
+#define	R_PS		32
+#define	R_PC		33
+#define	R_TRAPARG_A0	34
+#define	R_TRAPARG_A1	35
+#define	R_TRAPARG_A2	36
+
 struct reg {
 	u_int64_t	r_regs[32];
 };
diff --git a/sys/alpha/include/signal.h b/sys/alpha/include/signal.h
index 90a5a3927272..2e018642ff9a 100644
--- a/sys/alpha/include/signal.h
+++ b/sys/alpha/include/signal.h
@@ -32,6 +32,7 @@
 #define	_ALPHA_SIGNAL_H_
 
 typedef long	sig_atomic_t;
+
 #ifndef _ANSI_SOURCE
 
 /*
@@ -52,7 +53,6 @@ struct  osigcontext {
 	long	sc_pc;                  /* pc to restore */
 	long	sc_ps;			/* ps to restore */
 	unsigned long sc_regs[32];	/* integer register set (see above) */
-#define	sc_sp	sc_regs[R_SP]
 	long	sc_ownedfp;		/* fp has been used */
 	unsigned long sc_fpregs[32];	/* FP register set (see above) */
 	unsigned long sc_fpcr;		/* FP control register (see above) */
@@ -65,5 +65,29 @@ struct  osigcontext {
 	long	sc_xxx2[3];		/* sc_fp_trap_pc, sc_fp_trigger_sum, sc_fp_trigger_inst */
 };
 
+/*
+ * The sequence of the fields should match those in
+ * mcontext_t. Keep them in sync!
+ */
+struct	sigcontext {
+	sigset_t sc_mask;		/* signal mask to restore */
+	long	sc_onstack;             /* sigstack state to restore */
+	unsigned long sc_regs[32];	/* integer register set (see above) */
+	long	sc_ps;			/* ps to restore */
+	long	sc_pc;                  /* pc to restore */
+	unsigned long sc_traparg_a0;	/* a0 argument to trap at exception */
+	unsigned long sc_traparg_a1;	/* a1 argument to trap at exception */
+	unsigned long sc_traparg_a2;	/* a2 argument to trap at exception */
+	unsigned long sc_fpregs[32];	/* FP register set (see above) */
+	unsigned long sc_fpcr;		/* FP control register (see above) */
+	unsigned long sc_fp_control;	/* FP software control word */
+	long	sc_ownedfp;		/* fp has been used */
+	long	sc_xxx1[2];		/* sc_ssize, sc_sbase on DUX */
+	long	sc_xxx2[3];		/* sc_fp_trap_pc, sc_fp_trigger_sum, sc_fp_trigger_inst */
+	long	sc_reserved[2];		/* XXX */
+};
+
+#define	sc_sp	sc_regs[R_SP]
+
 #endif /* !_ANSI_SOURCE */
 #endif /* !_ALPHA_SIGNAL_H_*/
diff --git a/sys/alpha/include/ucontext.h b/sys/alpha/include/ucontext.h
index 66b9e51c8b9f..40a903789e93 100644
--- a/sys/alpha/include/ucontext.h
+++ b/sys/alpha/include/ucontext.h
@@ -29,18 +29,24 @@
  */
 
 #ifndef _MACHINE_UCONTEXT_H_
-#define _MACHINE_UCONTEXT_H_ 1
+#define	_MACHINE_UCONTEXT_H_
 
 #include <machine/frame.h>
 
-typedef struct {
-	struct trapframe mc_tf;
-	unsigned long	mc_fpregs[32];
-	unsigned long	mc_fpcr;
-	unsigned long	mc_fp_control;
-	unsigned long	mc_apcb_usp;
-	long		mc_ownedfp;
-	long		__spare__[8];
+typedef struct __mcontext {
+	/*
+	 * These fields must match the definition
+	 * of struct sigcontext. That way we can support
+	 * struct sigcontext and ucontext_t at the same
+	 * time.
+	 */
+	long	mc_onstack;		/* XXX - sigcontext compat. */
+	unsigned long mc_regs[37];
+	unsigned long mc_fpregs[32];
+	unsigned long mc_fpcr;
+	unsigned long mc_fp_control;
+	long	mc_ownedfp;
+	long	__spare__[7];
 } mcontext_t;
 
-#endif /* _MACHINE_UCONTEXT_H_ */
+#endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/amd64/amd64/genassym.c b/sys/amd64/amd64/genassym.c
index 62dbf5369c41..829917721f0a 100644
--- a/sys/amd64/amd64/genassym.c
+++ b/sys/amd64/amd64/genassym.c
@@ -69,11 +69,10 @@
 #include <machine/apic.h>
 #endif
 #include <machine/segments.h>
+#include <machine/sigframe.h>
 #include <machine/globaldata.h>
 #include <machine/vm86.h>
 
-#include <machine/sigframe.h>
-
 #define	OS(s, m)	((u_int)offsetof(struct s, m))
 
 int	main __P((void));
@@ -157,7 +156,8 @@ main()
 	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_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);
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 8b6bb842d77a..1ef6fb08aa2d 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -613,6 +613,7 @@ sendsig(catcher, sig, mask, code)
 	struct trapframe *regs;
 	struct sigacts *psp;
 	struct sigframe sf, *sfp;
+	int onstack;
 
 	p = curproc;
 
@@ -623,17 +624,18 @@ sendsig(catcher, sig, mask, code)
 
 	regs = p->p_md.md_regs;
 	psp = p->p_sigacts;
+	onstack = (psp->ps_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
 
 	/* save user context */
 	bzero(&sf, sizeof(struct sigframe));
 	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();
 
 	/* Allocate and validate space for the signal handler context. */
-        if ((psp->ps_flags & SAS_ALTSTACK) != 0 &&
-	    (psp->ps_sigstk.ss_flags & SS_ONSTACK) == 0 &&
+        if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(psp->ps_sigstk.ss_sp +
 		    psp->ps_sigstk.ss_size - sizeof(struct sigframe));
@@ -884,16 +886,13 @@ sigreturn(p, uap)
 {
 	struct trapframe *regs;
 	ucontext_t *ucp;
-	struct sigframe *sfp;
 	int cs, eflags;
 
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	sfp = (struct sigframe *)
-	    ((caddr_t)ucp - offsetof(struct sigframe, sf_uc));
 	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
 
-	if (useracc((caddr_t)sfp, sizeof(struct sigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
 
 	if (eflags & PSL_VM) {
@@ -963,7 +962,11 @@ sigreturn(p, uap)
 		*regs = ucp->uc_mcontext.mc_tf;
 	}
 
-	p->p_sigacts->ps_sigstk = ucp->uc_stack;
+	if (ucp->uc_mcontext.mc_onstack & 1)
+		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
+	else
+		p->p_sigacts->ps_sigstk.ss_flags &= ~SS_ONSTACK;
+
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
 	return(EJUSTRETURN);
diff --git a/sys/amd64/include/signal.h b/sys/amd64/include/signal.h
index e9f739e3a0b9..f02539e079ec 100644
--- a/sys/amd64/include/signal.h
+++ b/sys/amd64/include/signal.h
@@ -57,33 +57,62 @@ typedef int sig_atomic_t;
 typedef unsigned int osigset_t;
 
 struct	osigcontext {
-	int		sc_onstack;	/* sigstack state to restore */
-	osigset_t	sc_mask;	/* signal mask to restore */
-	int		sc_esp;		/* machine state */
-	int		sc_ebp;
-	int		sc_isp;
-	int		sc_eip;
-	int		sc_efl;
-	int		sc_es;
-	int		sc_ds;
-	int		sc_cs;
-	int		sc_ss;
-	int		sc_edi;
-	int		sc_esi;
-	int		sc_ebx;
-	int		sc_edx;
-	int		sc_ecx;
-	int		sc_eax;
-	int		sc_gs;
-	int		sc_fs;
+	int	sc_onstack;	/* sigstack state to restore */
+	osigset_t sc_mask;	/* signal mask to restore */
+	int	sc_esp;		/* machine state */
+	int	sc_ebp;
+	int	sc_isp;
+	int	sc_eip;
+	int	sc_efl;
+	int	sc_es;
+	int	sc_ds;
+	int	sc_cs;
+	int	sc_ss;
+	int	sc_edi;
+	int	sc_esi;
+	int	sc_ebx;
+	int	sc_edx;
+	int	sc_ecx;
+	int	sc_eax;
+	int	sc_gs;
+	int	sc_fs;
+	int	sc_trapno;
+	int	sc_err;
+};
+
+/*
+ * The sequence of the fields/registers in sigcontext should match
+ * those in mcontext_t.
+ */
+struct	sigcontext {
+	sigset_t sc_mask;		/* signal mask to restore */
+	int	sc_onstack;		/* sigstack state to restore */
+	int	sc_gs;
+	int	sc_fs;
+	int	sc_es;
+	int	sc_ds;
+	int	sc_edi;
+	int	sc_esi;
+	int	sc_ebp;
+	int	sc_isp;
+	int	sc_ebx;
+	int	sc_edx;
+	int	sc_ecx;
+	int	sc_eax;
+	int	sc_trapno;
+	int	sc_err;
+	int	sc_eip;
+	int	sc_cs;
+	int	sc_efl;
+	int	sc_esp;			/* machine state */
+	int	sc_ss;
+};
+
 #define sc_sp		sc_esp
 #define sc_fp		sc_ebp
 #define sc_pc		sc_eip
 #define sc_ps		sc_efl
 #define sc_eflags	sc_efl
-	int		sc_trapno;
-	int		sc_err;
-};
 
 #endif /* !_ANSI_SOURCE && !_POSIX_SOURCE */
 
diff --git a/sys/amd64/include/ucontext.h b/sys/amd64/include/ucontext.h
index bdf2e1df2307..0d7271621232 100644
--- a/sys/amd64/include/ucontext.h
+++ b/sys/amd64/include/ucontext.h
@@ -29,15 +29,22 @@
  */
 
 #ifndef _MACHINE_UCONTEXT_H_
-#define _MACHINE_UCONTEXT_H_ 1
+#define	_MACHINE_UCONTEXT_H_
 
 #include <machine/frame.h>
 
-typedef struct {
-	int		mc_gs;		/* %gs */
-	struct trapframe mc_tf;		/* trapframe */
-	int		mc_fpregs[28];	/* env87 + fpacc87 + u_long */
-	int		__spare__[17];
+typedef struct __mcontext {
+	/*
+	 * The first 3 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_fpregs[28];		/* env87 + fpacc87 + u_long */
+	int	__spare__[17];
 } mcontext_t;
 
-#endif /* _MACHINE_UCONTEXT_H_ */
+#endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/i386/i386/genassym.c b/sys/i386/i386/genassym.c
index 62dbf5369c41..829917721f0a 100644
--- a/sys/i386/i386/genassym.c
+++ b/sys/i386/i386/genassym.c
@@ -69,11 +69,10 @@
 #include <machine/apic.h>
 #endif
 #include <machine/segments.h>
+#include <machine/sigframe.h>
 #include <machine/globaldata.h>
 #include <machine/vm86.h>
 
-#include <machine/sigframe.h>
-
 #define	OS(s, m)	((u_int)offsetof(struct s, m))
 
 int	main __P((void));
@@ -157,7 +156,8 @@ main()
 	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_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);
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index 8b6bb842d77a..1ef6fb08aa2d 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -613,6 +613,7 @@ sendsig(catcher, sig, mask, code)
 	struct trapframe *regs;
 	struct sigacts *psp;
 	struct sigframe sf, *sfp;
+	int onstack;
 
 	p = curproc;
 
@@ -623,17 +624,18 @@ sendsig(catcher, sig, mask, code)
 
 	regs = p->p_md.md_regs;
 	psp = p->p_sigacts;
+	onstack = (psp->ps_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
 
 	/* save user context */
 	bzero(&sf, sizeof(struct sigframe));
 	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();
 
 	/* Allocate and validate space for the signal handler context. */
-        if ((psp->ps_flags & SAS_ALTSTACK) != 0 &&
-	    (psp->ps_sigstk.ss_flags & SS_ONSTACK) == 0 &&
+        if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(psp->ps_sigstk.ss_sp +
 		    psp->ps_sigstk.ss_size - sizeof(struct sigframe));
@@ -884,16 +886,13 @@ sigreturn(p, uap)
 {
 	struct trapframe *regs;
 	ucontext_t *ucp;
-	struct sigframe *sfp;
 	int cs, eflags;
 
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	sfp = (struct sigframe *)
-	    ((caddr_t)ucp - offsetof(struct sigframe, sf_uc));
 	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
 
-	if (useracc((caddr_t)sfp, sizeof(struct sigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
 
 	if (eflags & PSL_VM) {
@@ -963,7 +962,11 @@ sigreturn(p, uap)
 		*regs = ucp->uc_mcontext.mc_tf;
 	}
 
-	p->p_sigacts->ps_sigstk = ucp->uc_stack;
+	if (ucp->uc_mcontext.mc_onstack & 1)
+		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
+	else
+		p->p_sigacts->ps_sigstk.ss_flags &= ~SS_ONSTACK;
+
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
 	return(EJUSTRETURN);
diff --git a/sys/i386/include/signal.h b/sys/i386/include/signal.h
index e9f739e3a0b9..f02539e079ec 100644
--- a/sys/i386/include/signal.h
+++ b/sys/i386/include/signal.h
@@ -57,33 +57,62 @@ typedef int sig_atomic_t;
 typedef unsigned int osigset_t;
 
 struct	osigcontext {
-	int		sc_onstack;	/* sigstack state to restore */
-	osigset_t	sc_mask;	/* signal mask to restore */
-	int		sc_esp;		/* machine state */
-	int		sc_ebp;
-	int		sc_isp;
-	int		sc_eip;
-	int		sc_efl;
-	int		sc_es;
-	int		sc_ds;
-	int		sc_cs;
-	int		sc_ss;
-	int		sc_edi;
-	int		sc_esi;
-	int		sc_ebx;
-	int		sc_edx;
-	int		sc_ecx;
-	int		sc_eax;
-	int		sc_gs;
-	int		sc_fs;
+	int	sc_onstack;	/* sigstack state to restore */
+	osigset_t sc_mask;	/* signal mask to restore */
+	int	sc_esp;		/* machine state */
+	int	sc_ebp;
+	int	sc_isp;
+	int	sc_eip;
+	int	sc_efl;
+	int	sc_es;
+	int	sc_ds;
+	int	sc_cs;
+	int	sc_ss;
+	int	sc_edi;
+	int	sc_esi;
+	int	sc_ebx;
+	int	sc_edx;
+	int	sc_ecx;
+	int	sc_eax;
+	int	sc_gs;
+	int	sc_fs;
+	int	sc_trapno;
+	int	sc_err;
+};
+
+/*
+ * The sequence of the fields/registers in sigcontext should match
+ * those in mcontext_t.
+ */
+struct	sigcontext {
+	sigset_t sc_mask;		/* signal mask to restore */
+	int	sc_onstack;		/* sigstack state to restore */
+	int	sc_gs;
+	int	sc_fs;
+	int	sc_es;
+	int	sc_ds;
+	int	sc_edi;
+	int	sc_esi;
+	int	sc_ebp;
+	int	sc_isp;
+	int	sc_ebx;
+	int	sc_edx;
+	int	sc_ecx;
+	int	sc_eax;
+	int	sc_trapno;
+	int	sc_err;
+	int	sc_eip;
+	int	sc_cs;
+	int	sc_efl;
+	int	sc_esp;			/* machine state */
+	int	sc_ss;
+};
+
 #define sc_sp		sc_esp
 #define sc_fp		sc_ebp
 #define sc_pc		sc_eip
 #define sc_ps		sc_efl
 #define sc_eflags	sc_efl
-	int		sc_trapno;
-	int		sc_err;
-};
 
 #endif /* !_ANSI_SOURCE && !_POSIX_SOURCE */
 
diff --git a/sys/i386/include/ucontext.h b/sys/i386/include/ucontext.h
index bdf2e1df2307..0d7271621232 100644
--- a/sys/i386/include/ucontext.h
+++ b/sys/i386/include/ucontext.h
@@ -29,15 +29,22 @@
  */
 
 #ifndef _MACHINE_UCONTEXT_H_
-#define _MACHINE_UCONTEXT_H_ 1
+#define	_MACHINE_UCONTEXT_H_
 
 #include <machine/frame.h>
 
-typedef struct {
-	int		mc_gs;		/* %gs */
-	struct trapframe mc_tf;		/* trapframe */
-	int		mc_fpregs[28];	/* env87 + fpacc87 + u_long */
-	int		__spare__[17];
+typedef struct __mcontext {
+	/*
+	 * The first 3 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_fpregs[28];		/* env87 + fpacc87 + u_long */
+	int	__spare__[17];
 } mcontext_t;
 
-#endif /* _MACHINE_UCONTEXT_H_ */
+#endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/pc98/i386/machdep.c b/sys/pc98/i386/machdep.c
index 416443c5c15c..2eefb159aeab 100644
--- a/sys/pc98/i386/machdep.c
+++ b/sys/pc98/i386/machdep.c
@@ -627,6 +627,7 @@ sendsig(catcher, sig, mask, code)
 	struct trapframe *regs;
 	struct sigacts *psp;
 	struct sigframe sf, *sfp;
+	int onstack;
 
 	p = curproc;
 
@@ -637,17 +638,18 @@ sendsig(catcher, sig, mask, code)
 
 	regs = p->p_md.md_regs;
 	psp = p->p_sigacts;
+	onstack = (psp->ps_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
 
 	/* save user context */
 	bzero(&sf, sizeof(struct sigframe));
 	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();
 
 	/* Allocate and validate space for the signal handler context. */
-        if ((psp->ps_flags & SAS_ALTSTACK) != 0 &&
-	    (psp->ps_sigstk.ss_flags & SS_ONSTACK) == 0 &&
+        if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(psp->ps_sigstk.ss_sp +
 		    psp->ps_sigstk.ss_size - sizeof(struct sigframe));
@@ -897,16 +899,13 @@ sigreturn(p, uap)
 {
 	struct trapframe *regs;
 	ucontext_t *ucp;
-	struct sigframe *sfp;
 	int cs, eflags;
 
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	sfp = (struct sigframe *)
-	    ((caddr_t)ucp - offsetof(struct sigframe, sf_uc));
 	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
 
-	if (useracc((caddr_t)sfp, sizeof(struct sigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
 
 	if (eflags & PSL_VM) {
@@ -976,7 +975,11 @@ sigreturn(p, uap)
 		*regs = ucp->uc_mcontext.mc_tf;
 	}
 
-	p->p_sigacts->ps_sigstk = ucp->uc_stack;
+	if (ucp->uc_mcontext.mc_onstack & 1)
+		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
+	else
+		p->p_sigacts->ps_sigstk.ss_flags &= ~SS_ONSTACK;
+
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
 	return(EJUSTRETURN);
diff --git a/sys/pc98/pc98/machdep.c b/sys/pc98/pc98/machdep.c
index 416443c5c15c..2eefb159aeab 100644
--- a/sys/pc98/pc98/machdep.c
+++ b/sys/pc98/pc98/machdep.c
@@ -627,6 +627,7 @@ sendsig(catcher, sig, mask, code)
 	struct trapframe *regs;
 	struct sigacts *psp;
 	struct sigframe sf, *sfp;
+	int onstack;
 
 	p = curproc;
 
@@ -637,17 +638,18 @@ sendsig(catcher, sig, mask, code)
 
 	regs = p->p_md.md_regs;
 	psp = p->p_sigacts;
+	onstack = (psp->ps_sigstk.ss_flags & SS_ONSTACK) ? 1 : 0;
 
 	/* save user context */
 	bzero(&sf, sizeof(struct sigframe));
 	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();
 
 	/* Allocate and validate space for the signal handler context. */
-        if ((psp->ps_flags & SAS_ALTSTACK) != 0 &&
-	    (psp->ps_sigstk.ss_flags & SS_ONSTACK) == 0 &&
+        if ((psp->ps_flags & SAS_ALTSTACK) != 0 && !onstack &&
 	    SIGISMEMBER(psp->ps_sigonstack, sig)) {
 		sfp = (struct sigframe *)(psp->ps_sigstk.ss_sp +
 		    psp->ps_sigstk.ss_size - sizeof(struct sigframe));
@@ -897,16 +899,13 @@ sigreturn(p, uap)
 {
 	struct trapframe *regs;
 	ucontext_t *ucp;
-	struct sigframe *sfp;
 	int cs, eflags;
 
 	regs = p->p_md.md_regs;
 	ucp = uap->sigcntxp;
-	sfp = (struct sigframe *)
-	    ((caddr_t)ucp - offsetof(struct sigframe, sf_uc));
 	eflags = ucp->uc_mcontext.mc_tf.tf_eflags;
 
-	if (useracc((caddr_t)sfp, sizeof(struct sigframe), B_WRITE) == 0)
+	if (useracc((caddr_t)ucp, sizeof(ucontext_t), B_WRITE) == 0)
 		return(EFAULT);
 
 	if (eflags & PSL_VM) {
@@ -976,7 +975,11 @@ sigreturn(p, uap)
 		*regs = ucp->uc_mcontext.mc_tf;
 	}
 
-	p->p_sigacts->ps_sigstk = ucp->uc_stack;
+	if (ucp->uc_mcontext.mc_onstack & 1)
+		p->p_sigacts->ps_sigstk.ss_flags |= SS_ONSTACK;
+	else
+		p->p_sigacts->ps_sigstk.ss_flags &= ~SS_ONSTACK;
+
 	p->p_sigmask = ucp->uc_sigmask;
 	SIG_CANTMASK(p->p_sigmask);
 	return(EJUSTRETURN);
diff --git a/sys/sys/_sigset.h b/sys/sys/_sigset.h
index 8d1e7738474d..edddbbece69d 100644
--- a/sys/sys/_sigset.h
+++ b/sys/sys/_sigset.h
@@ -44,22 +44,20 @@
 
 #include <sys/cdefs.h>
 #include <sys/_posix.h>
-#include <sys/types.h>
-#include <machine/signal.h>	/* sig_atomic_t; trap codes; sigcontext */
 
 /*
- * sigset_t macros
+ * sigset_t macros.
  */
-#define _SIG_WORDS	4
-#define _SIG_MAXSIG	128
-#define _SIG_IDX(sig)	((sig) - 1)
-#define _SIG_WORD(sig)	(_SIG_IDX(sig) >> 5)
-#define _SIG_BIT(sig)	(1 << (_SIG_IDX(sig) & 31))
+#define	_SIG_WORDS	4
+#define	_SIG_MAXSIG	128
+#define	_SIG_IDX(sig)	((sig) - 1)
+#define	_SIG_WORD(sig)	(_SIG_IDX(sig) >> 5)
+#define	_SIG_BIT(sig)	(1 << (_SIG_IDX(sig) & 31))
 
 /*
- * system defined signals
+ * System defined signals.
  */
-#define SIGHUP		1	/* hangup */
+#define	SIGHUP		1	/* hangup */
 #define	SIGINT		2	/* interrupt */
 #define	SIGQUIT		3	/* quit */
 #define	SIGILL		4	/* illegal instr. (not reset when caught) */
@@ -98,11 +96,11 @@
 #define	SIGXFSZ		25	/* exceeded file size limit */
 #define	SIGVTALRM	26	/* virtual time alarm */
 #define	SIGPROF		27	/* profiling time alarm */
-#define SIGWINCH	28	/* window size changes */
-#define SIGINFO		29	/* information request */
+#define	SIGWINCH	28	/* window size changes */
+#define	SIGINFO		29	/* information request */
 #endif
-#define SIGUSR1		30	/* user defined signal 1 */
-#define SIGUSR2		31	/* user defined signal 2 */
+#define	SIGUSR1		30	/* user defined signal 1 */
+#define	SIGUSR2		31	/* user defined signal 2 */
 
 /*-
  * Type of a signal handling function.
@@ -124,50 +122,62 @@ typedef void __sighandler_t __P((int));
 
 #define	SIG_DFL		((__sighandler_t *)0)
 #define	SIG_IGN		((__sighandler_t *)1)
-#define SIG_HOLD	((__sighandler_t *)2)
+#define	SIG_HOLD	((__sighandler_t *)2)
 #define	SIG_ERR		((__sighandler_t *)-1)
 
+#ifndef _POSIX_SOURCE
 union sigval {
 	/* Members as suggested by Annex C of POSIX 1003.1b. */
-	int		sigval_int;
-	void		*sigval_ptr;
+	int	sigval_int;
+	void	*sigval_ptr;
 };
 
-typedef struct {
-	int		si_signo;		/* signal number */
-	int		si_errno;		/* errno association */
+typedef struct __siginfo {
+	int	si_signo;		/* signal number */
+	int	si_errno;		/* errno association */
 	/* 
 	 * Cause of signal, one of the SI_ macros or signal-specific
 	 * values, i.e. one of the FPE_... values for SIGFPE. This
 	 * value is equivalent to the second argument to an old-style
 	 * FreeBSD signal handler.
 	 */
-	int		si_code;		/* signal code */
-	pid_t		si_pid;			/* sending process */
-	uid_t		si_uid;			/* sender's ruid */
-	int		si_status;		/* exit value */
-	void		*si_addr;		/* faulting instruction */
-	union sigval	si_value;		/* signal value */
-	long		si_band;		/* band event for SIGPOLL */
-	int		__spare__[7];		/* gimme some slack */
+	int	si_code;		/* signal code */
+	int	si_pid;			/* sending process */
+	unsigned int si_uid;		/* sender's ruid */
+	int	si_status;		/* exit value */
+	void	*si_addr;		/* faulting instruction */
+	union sigval si_value;		/* signal value */
+	long	si_band;		/* band event for SIGPOLL */
+	int	__spare__[7];		/* gimme some slack */
 } siginfo_t;
+#endif
 
-typedef struct {
+typedef struct __sigset {
 	unsigned int	__bits[_SIG_WORDS];
 } sigset_t;
 
+/*
+ * XXX - there are some nasty dependencies.
+ * Now that sigset_t has been defined we can
+ * include the MD structures.
+ */     
+#include <machine/signal.h>     /* sig_atomic_t; trap codes; sigcontext */
+
 #if !defined(_ANSI_SOURCE)
 
+struct __siginfo;
+
 /*
  * Signal vector "template" used in sigaction call.
  */
 struct	sigaction {
 	union {
 		void    (*__sa_handler) __P((int));
-		void    (*__sa_sigaction) __P((int, siginfo_t *, void *));
+		void    (*__sa_sigaction) __P((int, struct __siginfo *,
+					       void *));
 	} __sigaction_u;		/* signal handler */
-	int		sa_flags;	/* see signal options below */
-	sigset_t 	sa_mask;	/* signal mask to apply */
+	int	sa_flags;		/* see signal options below */
+	sigset_t sa_mask;		/* signal mask to apply */
 };
 
 /* if SA_SIGINFO is set, sa_sigaction is to be used instead of sa_handler. */
@@ -189,7 +199,7 @@ struct	sigaction {
 #define	SA_USERTRAMP	0x0100	/* do not bounce off kernel's sigtramp */
 #endif
 
-#define NSIG		32
+#define NSIG		32	/* number of old signals (counting 0) */
 
 /* POSIX 1003.1b required values. */
 #define SI_USER		0x10001
@@ -211,12 +221,12 @@ typedef	_BSD_SIZE_T_	size_t;
 #endif
 
 /*
- * sigaltstack
+ * Structure used in sigaltstack call.
  */
 typedef struct sigaltstack {
-	char		*ss_sp;		/* signal stack base */
-	unsigned int	ss_size;	/* signal stack length */
-	int		ss_flags;	/* SS_DISABLE and/or SS_ONSTACK */
+	char	*ss_sp;			/* signal stack base */
+	size_t	ss_size;		/* signal stack length */
+	int	ss_flags;		/* SS_DISABLE and/or SS_ONSTACK */
 } stack_t;
 
 #define	SS_ONSTACK	0x0001	/* take signal on alternate stack */
@@ -224,9 +234,7 @@ typedef struct sigaltstack {
 #define	MINSIGSTKSZ	8192			/* minimum allowable stack */
 #define	SIGSTKSZ	(MINSIGSTKSZ + 32768)	/* recommended stack size */
 
-/*
- * Suck in definition of ucontext_t
- */
+/* Have enough typedefs for this now.  XXX */
 #include <sys/ucontext.h>
 
 /*
@@ -234,9 +242,9 @@ typedef struct sigaltstack {
  * Signal vector "template" used in sigvec call.
  */
 struct	sigvec {
-	__sighandler_t	*sv_handler;	/* signal handler */
-	int		sv_mask;	/* signal mask to apply */
-	int		sv_flags;	/* see signal options below */
+	__sighandler_t *sv_handler;	/* signal handler */
+	int	sv_mask;		/* signal mask to apply */
+	int	sv_flags;		/* see signal options below */
 };
 
 #define SV_ONSTACK	SA_ONSTACK
@@ -251,8 +259,8 @@ struct	sigvec {
  * Structure used in sigstack call.
  */
 struct	sigstack {
-	char		*ss_sp;			/* signal stack pointer */
-	int		ss_onstack;		/* current status */
+	char	*ss_sp;			/* signal stack pointer */
+	int	ss_onstack;		/* current status */
 };
 
 /*
@@ -272,14 +280,16 @@ struct	sigstack {
 #define	SIG_UNBLOCK	2	/* unblock specified signal set */
 #define	SIG_SETMASK	3	/* set specified signal set */
 
+#ifndef _POSIX_SOURCE
 struct sigevent {
-	int		sigev_notify;		/* Notification type */
-	int		sigev_signo;		/* Signal number */
-	union sigval	sigev_value;		/* Signal value */
+	int	sigev_notify;		/* Notification type */
+	int	sigev_signo;		/* Signal number */
+	union sigval sigev_value;	/* Signal value */
 };
 
 #define	SIGEV_NONE	0		/* No async notification */
 #define	SIGEV_SIGNAL	1		/* Generate a queued signal */
+#endif
 
 #endif /* !_ANSI_SOURCE */
 
diff --git a/sys/sys/signal.h b/sys/sys/signal.h
index 8d1e7738474d..edddbbece69d 100644
--- a/sys/sys/signal.h
+++ b/sys/sys/signal.h
@@ -44,22 +44,20 @@
 
 #include <sys/cdefs.h>
 #include <sys/_posix.h>
-#include <sys/types.h>
-#include <machine/signal.h>	/* sig_atomic_t; trap codes; sigcontext */
 
 /*
- * sigset_t macros
+ * sigset_t macros.
  */
-#define _SIG_WORDS	4
-#define _SIG_MAXSIG	128
-#define _SIG_IDX(sig)	((sig) - 1)
-#define _SIG_WORD(sig)	(_SIG_IDX(sig) >> 5)
-#define _SIG_BIT(sig)	(1 << (_SIG_IDX(sig) & 31))
+#define	_SIG_WORDS	4
+#define	_SIG_MAXSIG	128
+#define	_SIG_IDX(sig)	((sig) - 1)
+#define	_SIG_WORD(sig)	(_SIG_IDX(sig) >> 5)
+#define	_SIG_BIT(sig)	(1 << (_SIG_IDX(sig) & 31))
 
 /*
- * system defined signals
+ * System defined signals.
  */
-#define SIGHUP		1	/* hangup */
+#define	SIGHUP		1	/* hangup */
 #define	SIGINT		2	/* interrupt */
 #define	SIGQUIT		3	/* quit */
 #define	SIGILL		4	/* illegal instr. (not reset when caught) */
@@ -98,11 +96,11 @@
 #define	SIGXFSZ		25	/* exceeded file size limit */
 #define	SIGVTALRM	26	/* virtual time alarm */
 #define	SIGPROF		27	/* profiling time alarm */
-#define SIGWINCH	28	/* window size changes */
-#define SIGINFO		29	/* information request */
+#define	SIGWINCH	28	/* window size changes */
+#define	SIGINFO		29	/* information request */
 #endif
-#define SIGUSR1		30	/* user defined signal 1 */
-#define SIGUSR2		31	/* user defined signal 2 */
+#define	SIGUSR1		30	/* user defined signal 1 */
+#define	SIGUSR2		31	/* user defined signal 2 */
 
 /*-
  * Type of a signal handling function.
@@ -124,50 +122,62 @@ typedef void __sighandler_t __P((int));
 
 #define	SIG_DFL		((__sighandler_t *)0)
 #define	SIG_IGN		((__sighandler_t *)1)
-#define SIG_HOLD	((__sighandler_t *)2)
+#define	SIG_HOLD	((__sighandler_t *)2)
 #define	SIG_ERR		((__sighandler_t *)-1)
 
+#ifndef _POSIX_SOURCE
 union sigval {
 	/* Members as suggested by Annex C of POSIX 1003.1b. */
-	int		sigval_int;
-	void		*sigval_ptr;
+	int	sigval_int;
+	void	*sigval_ptr;
 };
 
-typedef struct {
-	int		si_signo;		/* signal number */
-	int		si_errno;		/* errno association */
+typedef struct __siginfo {
+	int	si_signo;		/* signal number */
+	int	si_errno;		/* errno association */
 	/* 
 	 * Cause of signal, one of the SI_ macros or signal-specific
 	 * values, i.e. one of the FPE_... values for SIGFPE. This
 	 * value is equivalent to the second argument to an old-style
 	 * FreeBSD signal handler.
 	 */
-	int		si_code;		/* signal code */
-	pid_t		si_pid;			/* sending process */
-	uid_t		si_uid;			/* sender's ruid */
-	int		si_status;		/* exit value */
-	void		*si_addr;		/* faulting instruction */
-	union sigval	si_value;		/* signal value */
-	long		si_band;		/* band event for SIGPOLL */
-	int		__spare__[7];		/* gimme some slack */
+	int	si_code;		/* signal code */
+	int	si_pid;			/* sending process */
+	unsigned int si_uid;		/* sender's ruid */
+	int	si_status;		/* exit value */
+	void	*si_addr;		/* faulting instruction */
+	union sigval si_value;		/* signal value */
+	long	si_band;		/* band event for SIGPOLL */
+	int	__spare__[7];		/* gimme some slack */
 } siginfo_t;
+#endif
 
-typedef struct {
+typedef struct __sigset {
 	unsigned int	__bits[_SIG_WORDS];
 } sigset_t;
 
+/*
+ * XXX - there are some nasty dependencies.
+ * Now that sigset_t has been defined we can
+ * include the MD structures.
+ */     
+#include <machine/signal.h>     /* sig_atomic_t; trap codes; sigcontext */
+
 #if !defined(_ANSI_SOURCE)
 
+struct __siginfo;
+
 /*
  * Signal vector "template" used in sigaction call.
  */
 struct	sigaction {
 	union {
 		void    (*__sa_handler) __P((int));
-		void    (*__sa_sigaction) __P((int, siginfo_t *, void *));
+		void    (*__sa_sigaction) __P((int, struct __siginfo *,
+					       void *));
 	} __sigaction_u;		/* signal handler */
-	int		sa_flags;	/* see signal options below */
-	sigset_t 	sa_mask;	/* signal mask to apply */
+	int	sa_flags;		/* see signal options below */
+	sigset_t sa_mask;		/* signal mask to apply */
 };
 
 /* if SA_SIGINFO is set, sa_sigaction is to be used instead of sa_handler. */
@@ -189,7 +199,7 @@ struct	sigaction {
 #define	SA_USERTRAMP	0x0100	/* do not bounce off kernel's sigtramp */
 #endif
 
-#define NSIG		32
+#define NSIG		32	/* number of old signals (counting 0) */
 
 /* POSIX 1003.1b required values. */
 #define SI_USER		0x10001
@@ -211,12 +221,12 @@ typedef	_BSD_SIZE_T_	size_t;
 #endif
 
 /*
- * sigaltstack
+ * Structure used in sigaltstack call.
  */
 typedef struct sigaltstack {
-	char		*ss_sp;		/* signal stack base */
-	unsigned int	ss_size;	/* signal stack length */
-	int		ss_flags;	/* SS_DISABLE and/or SS_ONSTACK */
+	char	*ss_sp;			/* signal stack base */
+	size_t	ss_size;		/* signal stack length */
+	int	ss_flags;		/* SS_DISABLE and/or SS_ONSTACK */
 } stack_t;
 
 #define	SS_ONSTACK	0x0001	/* take signal on alternate stack */
@@ -224,9 +234,7 @@ typedef struct sigaltstack {
 #define	MINSIGSTKSZ	8192			/* minimum allowable stack */
 #define	SIGSTKSZ	(MINSIGSTKSZ + 32768)	/* recommended stack size */
 
-/*
- * Suck in definition of ucontext_t
- */
+/* Have enough typedefs for this now.  XXX */
 #include <sys/ucontext.h>
 
 /*
@@ -234,9 +242,9 @@ typedef struct sigaltstack {
  * Signal vector "template" used in sigvec call.
  */
 struct	sigvec {
-	__sighandler_t	*sv_handler;	/* signal handler */
-	int		sv_mask;	/* signal mask to apply */
-	int		sv_flags;	/* see signal options below */
+	__sighandler_t *sv_handler;	/* signal handler */
+	int	sv_mask;		/* signal mask to apply */
+	int	sv_flags;		/* see signal options below */
 };
 
 #define SV_ONSTACK	SA_ONSTACK
@@ -251,8 +259,8 @@ struct	sigvec {
  * Structure used in sigstack call.
  */
 struct	sigstack {
-	char		*ss_sp;			/* signal stack pointer */
-	int		ss_onstack;		/* current status */
+	char	*ss_sp;			/* signal stack pointer */
+	int	ss_onstack;		/* current status */
 };
 
 /*
@@ -272,14 +280,16 @@ struct	sigstack {
 #define	SIG_UNBLOCK	2	/* unblock specified signal set */
 #define	SIG_SETMASK	3	/* set specified signal set */
 
+#ifndef _POSIX_SOURCE
 struct sigevent {
-	int		sigev_notify;		/* Notification type */
-	int		sigev_signo;		/* Signal number */
-	union sigval	sigev_value;		/* Signal value */
+	int	sigev_notify;		/* Notification type */
+	int	sigev_signo;		/* Signal number */
+	union sigval sigev_value;	/* Signal value */
 };
 
 #define	SIGEV_NONE	0		/* No async notification */
 #define	SIGEV_SIGNAL	1		/* Generate a queued signal */
+#endif
 
 #endif /* !_ANSI_SOURCE */
 
diff --git a/sys/sys/ucontext.h b/sys/sys/ucontext.h
index fda8bcd87f0f..b28c685ebd5e 100644
--- a/sys/sys/ucontext.h
+++ b/sys/sys/ucontext.h
@@ -29,16 +29,25 @@
  */
 
 #ifndef _SYS_UCONTEXT_H_
-#define _SYS_UCONTEXT_H_ 1
+#define	_SYS_UCONTEXT_H_
 
 #include <machine/ucontext.h>
 
 typedef struct __ucontext {
-        struct __ucontext *uc_link;
-        stack_t         uc_stack;
-        sigset_t        uc_sigmask;
-        mcontext_t      uc_mcontext;
-        int             __spare__[8];
+	/*
+	 * Keep the order of the first three fields. Also,
+	 * keep them the first to fields in the structure.
+	 * This way we can have a union with struct
+	 * sigcontext and ucontext_t. This allows us to
+	 * support them both at the same time.
+	 * note: the union is not defined, though.
+	 */
+	sigset_t	uc_sigmask;
+	stack_t		uc_stack;
+	mcontext_t	uc_mcontext;
+
+	struct __ucontext_t *uc_link;
+	int		__spare__[8];
 } ucontext_t;
 
-#endif /* _SYS_UCONTEXT_H_ */
+#endif /* !_SYS_UCONTEXT_H_ */