Add getcontext, setcontext, and swapcontext as system calls.

Previously these were libc functions but were requested to
be made into system calls for atomicity and to coalesce what
might be two entrances into the kernel (signal mask setting
and floating point trap) into one.

A few style nits and comments from bde are also included.

Tested on alpha by: gallatin

22 files changed, 371 insertions, 55 deletions

diff --git a/sys/alpha/alpha/machdep.c b/sys/alpha/alpha/machdep.c
index 7a4a001..ddf67d7 100644
--- a/sys/alpha/alpha/machdep.c
+++ b/sys/alpha/alpha/machdep.c
@@ -210,7 +210,9 @@ static void freebsd4_sendsig(sig_t catcher, int sig, sigset_t *mask,
     u_long code);
 #endif
 
+static void get_fpcontext(struct thread *td, mcontext_t *mcp);
 static void identifycpu(void);
+static int  set_fpcontext(struct thread *td, const mcontext_t *mcp);
 
 struct kva_md_info kmi;
 
@@ -1405,7 +1407,7 @@ sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
 	    frame->tf_regs[FRAME_TRAPARG_A1];
 	sf.sf_uc.uc_mcontext.mc_regs[R_TRAPARG_A2] =
 	    frame->tf_regs[FRAME_TRAPARG_A2];
-	sf.sf_uc.uc_mcontext.mc_format = __UC_REV0_SIGFRAME;
+	sf.sf_uc.uc_mcontext.mc_format = _MC_REV0_SIGFRAME;
 
 	/*
 	 * Allocate and validate space for the signal handler
@@ -1664,13 +1666,15 @@ sigreturn(struct thread *td,
 		return (error);
 	}
 #ifdef COMPAT_43
-	 if (((struct osigcontext*)&uc)->sc_regs[R_ZERO] == 0xACEDBADE)
-		  return osigreturn(td, (struct osigreturn_args *)uap);
+	if (((struct osigcontext*)&uc)->sc_regs[R_ZERO] == 0xACEDBADE)
+		return osigreturn(td, (struct osigreturn_args *)uap);
 #endif
 
 	/*
 	 * Restore the user-supplied information
 	 */
+	if ((error = set_fpcontext(td, &uc.uc_mcontext)) != 0)
+		return (error);
 	set_regs(td, (struct reg *)uc.uc_mcontext.mc_regs);
 	val = (uc.uc_mcontext.mc_regs[R_PS] | ALPHA_PSL_USERSET) &
 	    ~ALPHA_PSL_USERCLR;
@@ -1692,12 +1696,6 @@ sigreturn(struct thread *td,
 	signotify(p);
 	PROC_UNLOCK(p);
 
-	/* XXX ksc.sc_ownedfp ? */
-	alpha_fpstate_drop(td);
-	bcopy((struct fpreg *)uc.uc_mcontext.mc_fpregs,
-	      &td->td_pcb->pcb_fp, sizeof(struct fpreg));
-	td->td_pcb->pcb_fp_control = uc.uc_mcontext.mc_fp_control;
-
 	return (EJUSTRETURN);
 }
 
@@ -2011,6 +2009,133 @@ set_regs(td, regs)
 }
 
 int
+get_mcontext(struct thread *td, mcontext_t *mcp)
+{
+	/*
+	 * Use a trapframe for getsetcontext, so just copy the
+	 * threads trapframe.
+	 */
+	bcopy(&td->td_frame, &mcp->mc_regs, sizeof(td->td_frame));
+
+	/*
+	 * When the thread is the current thread, the user stack pointer
+	 * is not in the PCB; it must be read from the PAL.
+	 */
+	if (td == curthread)
+		mcp->mc_regs[FRAME_SP] = alpha_pal_rdusp();
+
+	mcp->mc_format = _MC_REV0_TRAPFRAME;
+	mcp->mc_onstack = sigonstack(alpha_pal_rdusp()) ? 1 : 0;
+	get_fpcontext(td, mcp);
+	return (0);
+}
+
+int
+set_mcontext(struct thread *td, const mcontext_t *mcp)
+{
+	int ret;
+	unsigned long val;
+
+	if ((mcp->mc_format != _MC_REV0_TRAPFRAME) &&
+	    (mcp->mc_format != _MC_REV0_SIGFRAME))
+		return (EINVAL);
+	else if ((ret = set_fpcontext(td, mcp)) != 0)
+		return (ret);
+
+	if (mcp->mc_format == _MC_REV0_SIGFRAME) {
+		set_regs(td, (struct reg *)&mcp->mc_regs);
+		val = (mcp->mc_regs[R_PS] | ALPHA_PSL_USERSET) &
+		    ~ALPHA_PSL_USERCLR;
+		td->td_frame->tf_regs[FRAME_PS] = val;
+		td->td_frame->tf_regs[FRAME_PC] = mcp->mc_regs[R_PC];
+		td->td_frame->tf_regs[FRAME_FLAGS] = 0;
+		if (td == curthread)
+			alpha_pal_wrusp(mcp->mc_regs[R_SP]);
+
+	} else {
+		if (td == curthread)
+			alpha_pal_wrusp(mcp->mc_regs[FRAME_SP]);
+		/*
+		 * The context is a trapframe, so just copy it over the
+		 * threads frame.
+		 */
+		bcopy(&mcp->mc_regs, &td->td_frame, sizeof(td->td_frame));
+	}
+	return (0);
+}
+
+static void
+get_fpcontext(struct thread *td, mcontext_t *mcp)
+{
+	register_t s;
+
+	s = intr_disable();
+	if ((td->td_md.md_flags & MDTD_FPUSED) == 0) {
+		intr_restore(s);
+		mcp->mc_ownedfp = _MC_FPOWNED_NONE;
+	} else if (PCPU_GET(fpcurthread) == td) {
+		/* See comments in alpha_fpstate_save() regarding FEN. */
+		if (td != curthread)
+			alpha_pal_wrfen(1);
+		/*
+		 * The last field (fpr_cr) of struct fpreg isn't
+		 * included in mc_fpregs, but it immediately follows
+		 * it in mcontext_t.
+		 */
+		savefpstate((struct fpreg *)&mcp->mc_fpregs);
+		if (td != curthread)
+			alpha_pal_wrfen(0);
+		intr_restore(s);
+		mcp->mc_ownedfp = _MC_FPOWNED_FPU;
+	} else {
+		/*
+		 * The thread doesn't own the FPU so get the state from
+		 * the PCB.
+		 */
+		intr_restore(s);
+		bcopy(&td->td_pcb->pcb_fp, &mcp->mc_fpregs,
+		    sizeof(td->td_pcb->pcb_fp));
+		mcp->mc_ownedfp = _MC_FPOWNED_PCB;
+	}
+	/* There's no harm in always doing the following. */
+	mcp->mc_fp_control = td->td_pcb->pcb_fp_control;
+}
+
+static int
+set_fpcontext(struct thread *td, const mcontext_t *mcp)
+{
+	register_t s;
+
+	if (mcp->mc_ownedfp == _MC_FPOWNED_NONE) {
+		/* XXX - Drop fpu state so we get a clean state? */
+		alpha_fpstate_drop(td);
+	}
+	else if ((mcp->mc_ownedfp != _MC_FPOWNED_FPU) &&
+	    (mcp->mc_ownedfp != _MC_FPOWNED_PCB))
+		return (EINVAL);
+	else {
+		s = intr_disable();
+		if (PCPU_GET(fpcurthread) == td) {
+			/*
+			 * The last field (fpr_cr) of struct fpreg isn't
+			 * included in mc_fpregs, but it immediately follows
+			 * it in mcontext_t.
+			 */
+			restorefpstate((struct fpreg *)&mcp->mc_fpregs);
+			intr_restore(s);
+		}
+		else {
+			/* Just save the state in the PCB. */
+			intr_restore(s);
+			bcopy(&mcp->mc_fpregs, &td->td_pcb->pcb_fp,
+			    sizeof (td->td_pcb->pcb_fp));
+		}
+		td->td_pcb->pcb_fp_control = mcp->mc_fp_control;
+	}
+	return (0);
+}
+
+int
 fill_dbregs(struct thread *td, struct dbreg *dbregs)
 {
 
diff --git a/sys/alpha/include/cpu.h b/sys/alpha/include/cpu.h
index 9d05765..0e39182 100644
--- a/sys/alpha/include/cpu.h
+++ b/sys/alpha/include/cpu.h
@@ -115,11 +115,11 @@ void	XentRestart(void);					/* MAGIC */
 void	XentSys(u_int64_t, u_int64_t, u_int64_t);		/* MAGIC */
 void	XentUna(u_int64_t, u_int64_t, u_int64_t);		/* MAGIC */
 void	alpha_init(u_long, u_long, u_long, u_long, u_long);
+void	alpha_fpstate_check(struct thread *td);
+void	alpha_fpstate_drop(struct thread *td);
+void	alpha_fpstate_save(struct thread *td, int write);
+void	alpha_fpstate_switch(struct thread *td);
 int	alpha_pa_access(u_long);
-void	alpha_fpstate_check(struct thread *p);
-void	alpha_fpstate_save(struct thread *p, int write);
-void	alpha_fpstate_drop(struct thread *p);
-void	alpha_fpstate_switch(struct thread *p);
 int	badaddr	(void *, size_t);
 int	badaddr_read(void *, size_t, void *);
 u_int64_t console_restart(u_int64_t, u_int64_t, u_int64_t);
diff --git a/sys/alpha/include/fpu.h b/sys/alpha/include/fpu.h
index 712a1f9..9f4800f 100644
--- a/sys/alpha/include/fpu.h
+++ b/sys/alpha/include/fpu.h
@@ -116,9 +116,7 @@
 	__asm__("trapb")
 
 #ifdef _KERNEL
-
-extern int fp_software_completion(u_int64_t regmask, struct thread *p);
-
+extern int fp_software_completion(u_int64_t regmask, struct thread *td);
 #endif
 
 #endif /* ! _MACHINE_FPU_H_ */
diff --git a/sys/alpha/include/signal.h b/sys/alpha/include/signal.h
index 2a1f17b..37a969e 100644
--- a/sys/alpha/include/signal.h
+++ b/sys/alpha/include/signal.h
@@ -94,10 +94,9 @@ struct sigcontext {
 	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 */
+	long	sc_ownedfp;		/* fp has been used; see mcontext_t */
+	long	sc_format;		/* see mcontext_t */
+	long	sc_spare[6];		/* XXX */
 };
 
 #define	sc_sp	sc_regs[R_SP]
diff --git a/sys/alpha/include/ucontext.h b/sys/alpha/include/ucontext.h
index bfc18df..2c3ed70 100644
--- a/sys/alpha/include/ucontext.h
+++ b/sys/alpha/include/ucontext.h
@@ -43,11 +43,14 @@ typedef struct __mcontext {
 	unsigned long mc_fpregs[32];
 	unsigned long mc_fpcr;
 	unsigned long mc_fp_control;
+#define	_MC_FPOWNED_NONE	0	/* FP state not used */
+#define	_MC_FPOWNED_FPU		1	/* FP state came from FPU */
+#define	_MC_FPOWNED_PCB		2	/* FP state came from PCB */
 	long	mc_ownedfp;
-#define	__UC_REV0_SIGFRAME	1	/* context is a signal frame */
-#define	__UC_REV0_TRAPFRAME	2	/* context is a trap frame */
+#define	_MC_REV0_SIGFRAME	1	/* context is a signal frame */
+#define	_MC_REV0_TRAPFRAME	2	/* context is a trap frame */
 	long	mc_format;
-	long	__spare__[6];
+	long	mc_spare[6];
 } mcontext_t;
 
 #if defined(_KERNEL) && defined(COMPAT_FREEBSD4)
diff --git a/sys/amd64/amd64/fpu.c b/sys/amd64/amd64/fpu.c
index 3395c99..661a698 100644
--- a/sys/amd64/amd64/fpu.c
+++ b/sys/amd64/amd64/fpu.c
@@ -161,14 +161,14 @@ void	stop_emulating(void);
 
 typedef u_char bool_t;
 
+static	void	fpusave(union savefpu *);
+static	void	fpurstor(union savefpu *);
 static	int	npx_attach(device_t dev);
 static	void	npx_identify(driver_t *driver, device_t parent);
 #ifndef SMP
 static	void	npx_intr(void *);
 #endif
 static	int	npx_probe(device_t dev);
-static	void	fpusave(union savefpu *);
-static	void	fpurstor(union savefpu *);
 #ifdef I586_CPU_XXX
 static	long	timezero(const char *funcname,
 		    void (*func)(void *buf, size_t len));
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 181463e..1aedc3d 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -2317,7 +2317,7 @@ set_fpregs(struct thread *td, struct fpreg *fpregs)
 /*
  * Get machine context.
  */
-void
+int
 get_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct trapframe *tp;
@@ -2344,6 +2344,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp)
 	mcp->mc_ss = tp->tf_ss;
 	mcp->mc_len = sizeof(*mcp);
 	get_fpcontext(td, mcp);
+	return (0);
 }
 
 /*
diff --git a/sys/amd64/include/signal.h b/sys/amd64/include/signal.h
index 29a9776..efc7ef0 100644
--- a/sys/amd64/include/signal.h
+++ b/sys/amd64/include/signal.h
@@ -119,7 +119,7 @@ struct sigcontext {
 	int	sc_efl;
 	int	sc_esp;
 	int	sc_ss;
-	int	sc_len;			/* sizeof(struct mcontext_t) */
+	int	sc_len;			/* sizeof(mcontext_t) */
 	/*
 	 * XXX - See <machine/ucontext.h> and <machine/npx.h> for
 	 *       the following fields.
@@ -127,7 +127,7 @@ struct sigcontext {
 	int	sc_fpformat;
 	int	sc_ownedfp;
 	int	sc_spare1[1];
-	int	sc_fpregs[128];
+	int	sc_fpstate[128];
 	int	sc_spare2[8];
 };
 
diff --git a/sys/amd64/include/ucontext.h b/sys/amd64/include/ucontext.h
index af9b4fd..ea6f0b6 100644
--- a/sys/amd64/include/ucontext.h
+++ b/sys/amd64/include/ucontext.h
@@ -38,7 +38,7 @@ typedef struct __mcontext {
 	 * and ucontext_t at the same time.
 	 */
 	int	mc_onstack;		/* XXX - sigcontext compat. */
-	int	mc_gs;
+	int	mc_gs;			/* machine state (trapframe) */
 	int	mc_fs;
 	int	mc_es;
 	int	mc_ds;
@@ -55,7 +55,7 @@ typedef struct __mcontext {
 	int	mc_eip;
 	int	mc_cs;
 	int	mc_eflags;
-	int	mc_esp;			/* machine state */
+	int	mc_esp;
 	int	mc_ss;
 
 	int	mc_len;			/* sizeof(mcontext_t) */
@@ -72,8 +72,7 @@ typedef struct __mcontext {
 	int	mc_spare2[8];
 } mcontext_t;
 
-#ifdef _KERNEL
-#ifdef COMPAT_FREEBSD4
+#if defined(_KERNEL) && defined(COMPAT_FREEBSD4)
 /* For 4.x binaries */
 struct mcontext4 {
 	int	mc_onstack;		/* XXX - sigcontext compat. */
@@ -101,10 +100,4 @@ struct mcontext4 {
 };
 #endif
 
-struct thread;
-
-void	get_mcontext(struct thread *td, mcontext_t *mcp);
-int	set_mcontext(struct thread *td, const mcontext_t *mcp);
-#endif
-
 #endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/amd64/isa/npx.c b/sys/amd64/isa/npx.c
index 3395c99..661a698 100644
--- a/sys/amd64/isa/npx.c
+++ b/sys/amd64/isa/npx.c
@@ -161,14 +161,14 @@ void	stop_emulating(void);
 
 typedef u_char bool_t;
 
+static	void	fpusave(union savefpu *);
+static	void	fpurstor(union savefpu *);
 static	int	npx_attach(device_t dev);
 static	void	npx_identify(driver_t *driver, device_t parent);
 #ifndef SMP
 static	void	npx_intr(void *);
 #endif
 static	int	npx_probe(device_t dev);
-static	void	fpusave(union savefpu *);
-static	void	fpurstor(union savefpu *);
 #ifdef I586_CPU_XXX
 static	long	timezero(const char *funcname,
 		    void (*func)(void *buf, size_t len));
diff --git a/sys/conf/files b/sys/conf/files
index 300fe54..c562b1b 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -975,6 +975,7 @@ kern/kern_alq.c		optional alq
 kern/kern_clock.c	standard
 kern/kern_condvar.c	standard
 kern/kern_conf.c	standard
+kern/kern_context.c	standard
 kern/kern_descrip.c	standard
 kern/kern_poll.c	optional device_polling
 kern/kern_environment.c	standard
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index 181463e..1aedc3d 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -2317,7 +2317,7 @@ set_fpregs(struct thread *td, struct fpreg *fpregs)
 /*
  * Get machine context.
  */
-void
+int
 get_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct trapframe *tp;
@@ -2344,6 +2344,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp)
 	mcp->mc_ss = tp->tf_ss;
 	mcp->mc_len = sizeof(*mcp);
 	get_fpcontext(td, mcp);
+	return (0);
 }
 
 /*
diff --git a/sys/i386/include/signal.h b/sys/i386/include/signal.h
index 29a9776..efc7ef0 100644
--- a/sys/i386/include/signal.h
+++ b/sys/i386/include/signal.h
@@ -119,7 +119,7 @@ struct sigcontext {
 	int	sc_efl;
 	int	sc_esp;
 	int	sc_ss;
-	int	sc_len;			/* sizeof(struct mcontext_t) */
+	int	sc_len;			/* sizeof(mcontext_t) */
 	/*
 	 * XXX - See <machine/ucontext.h> and <machine/npx.h> for
 	 *       the following fields.
@@ -127,7 +127,7 @@ struct sigcontext {
 	int	sc_fpformat;
 	int	sc_ownedfp;
 	int	sc_spare1[1];
-	int	sc_fpregs[128];
+	int	sc_fpstate[128];
 	int	sc_spare2[8];
 };
 
diff --git a/sys/i386/include/ucontext.h b/sys/i386/include/ucontext.h
index af9b4fd..ea6f0b6 100644
--- a/sys/i386/include/ucontext.h
+++ b/sys/i386/include/ucontext.h
@@ -38,7 +38,7 @@ typedef struct __mcontext {
 	 * and ucontext_t at the same time.
 	 */
 	int	mc_onstack;		/* XXX - sigcontext compat. */
-	int	mc_gs;
+	int	mc_gs;			/* machine state (trapframe) */
 	int	mc_fs;
 	int	mc_es;
 	int	mc_ds;
@@ -55,7 +55,7 @@ typedef struct __mcontext {
 	int	mc_eip;
 	int	mc_cs;
 	int	mc_eflags;
-	int	mc_esp;			/* machine state */
+	int	mc_esp;
 	int	mc_ss;
 
 	int	mc_len;			/* sizeof(mcontext_t) */
@@ -72,8 +72,7 @@ typedef struct __mcontext {
 	int	mc_spare2[8];
 } mcontext_t;
 
-#ifdef _KERNEL
-#ifdef COMPAT_FREEBSD4
+#if defined(_KERNEL) && defined(COMPAT_FREEBSD4)
 /* For 4.x binaries */
 struct mcontext4 {
 	int	mc_onstack;		/* XXX - sigcontext compat. */
@@ -101,10 +100,4 @@ struct mcontext4 {
 };
 #endif
 
-struct thread;
-
-void	get_mcontext(struct thread *td, mcontext_t *mcp);
-int	set_mcontext(struct thread *td, const mcontext_t *mcp);
-#endif
-
 #endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/i386/isa/npx.c b/sys/i386/isa/npx.c
index 3395c99..661a698 100644
--- a/sys/i386/isa/npx.c
+++ b/sys/i386/isa/npx.c
@@ -161,14 +161,14 @@ void	stop_emulating(void);
 
 typedef u_char bool_t;
 
+static	void	fpusave(union savefpu *);
+static	void	fpurstor(union savefpu *);
 static	int	npx_attach(device_t dev);
 static	void	npx_identify(driver_t *driver, device_t parent);
 #ifndef SMP
 static	void	npx_intr(void *);
 #endif
 static	int	npx_probe(device_t dev);
-static	void	fpusave(union savefpu *);
-static	void	fpurstor(union savefpu *);
 #ifdef I586_CPU_XXX
 static	long	timezero(const char *funcname,
 		    void (*func)(void *buf, size_t len));
diff --git a/sys/ia64/ia64/machdep.c b/sys/ia64/ia64/machdep.c
index df7dc4a..3bb9e34 100644
--- a/sys/ia64/ia64/machdep.c
+++ b/sys/ia64/ia64/machdep.c
@@ -1038,6 +1038,20 @@ freebsd4_sigreturn(struct thread *td, struct freebsd4_sigreturn_args *uap)
 }
 #endif
 
+int
+get_mcontext(struct thread *td, mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
+int
+set_mcontext(struct thread *td, const mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
 /*
  * Machine dependent boot() routine
  */
diff --git a/sys/kern/kern_context.c b/sys/kern/kern_context.c
new file mode 100644
index 0000000..1cc0eac
--- /dev/null
+++ b/sys/kern/kern_context.c
@@ -0,0 +1,134 @@
+/*-
+ * Copyright (c) 2002 Daniel M. Eischen <deischen@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+/*
+ * $FreeBSD$
+ */
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/proc.h>
+#include <sys/sysent.h>
+#include <sys/systm.h>
+#include <sys/sysproto.h>
+#include <sys/signalvar.h>
+#include <sys/ucontext.h>
+
+/*
+ * The first two fields of a ucontext_t are the signal mask and
+ * the machine context.  The next field is uc_link; we want to
+ * avoid destroying the link when copying out contexts.
+ */
+#define	UC_COPY_SIZE	(sizeof(sigset_t) + sizeof(mcontext_t))
+
+
+#ifndef _SYS_SYSPROTO_H_
+struct getcontext_args {
+	struct __ucontext *ucp;
+}
+struct setcontext_args {
+	const struct __ucontext_t *ucp;
+}
+struct swapcontext_args {
+	struct __ucontext *oucp;
+	const struct __ucontext_t *ucp;
+}
+#endif
+
+/*
+ * MPSAFE
+ */
+int
+getcontext(struct thread *td, struct getcontext_args *uap)
+{
+	ucontext_t uc;
+	int ret;	
+
+	if (uap->ucp == NULL)
+		ret = EINVAL;
+	else {
+		get_mcontext(td, &uc.uc_mcontext);
+		uc.uc_sigmask = td->td_proc->p_sigmask;
+		ret = copyout(&uc, uap->ucp, UC_COPY_SIZE);
+	}
+	return (ret);
+}
+
+/*
+ * MPSAFE
+ */
+int
+setcontext(struct thread *td, struct setcontext_args *uap)
+{
+	ucontext_t uc;
+	int ret;	
+
+	if (uap->ucp == NULL)
+		ret = EINVAL;
+	else {
+		ret = copyin(uap->ucp, &uc, UC_COPY_SIZE);
+		if (ret == 0) {
+			ret = set_mcontext(td, &uc.uc_mcontext);
+			if (ret == 0) {
+				SIG_CANTMASK(uc.uc_sigmask);
+				PROC_LOCK(td->td_proc);
+				td->td_proc->p_sigmask = uc.uc_sigmask;
+				PROC_UNLOCK(td->td_proc);
+			}
+		}
+	}
+	return (ret);
+}
+
+int
+swapcontext(struct thread *td, struct swapcontext_args *uap)
+{
+	ucontext_t uc;
+	int ret;	
+
+	if (uap->oucp == NULL || uap->ucp == NULL)
+		ret = EINVAL;
+	else {
+		get_mcontext(td, &uc.uc_mcontext);
+		uc.uc_sigmask = td->td_proc->p_sigmask;
+		ret = copyout(&uc, uap->oucp, UC_COPY_SIZE);
+		if (ret == 0) {
+			ret = copyin(uap->ucp, &uc, UC_COPY_SIZE);
+			if (ret == 0) {
+				ret = set_mcontext(td, &uc.uc_mcontext);
+				if (ret == 0) {
+					SIG_CANTMASK(uc.uc_sigmask);
+					PROC_LOCK(td->td_proc);
+					td->td_proc->p_sigmask = uc.uc_sigmask;
+					PROC_UNLOCK(td->td_proc);
+				}
+			}
+		}
+	}
+	return (ret);
+}
diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
index 650c65b..a41eb12 100644
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -608,6 +608,10 @@
 418	UNIMPL	BSD	__xstat
 419	UNIMPL	BSD	__xfstat
 420	UNIMPL	BSD	__xlstat
+421	MSTD	BSD	{ int getcontext(struct __ucontext *ucp); }
+422	MSTD	BSD	{ int setcontext(const struct __ucontext *ucp); }
+423	MSTD	BSD	{ int swapcontext(struct __ucontext *oucp, \
+			    const struct __ucontext *ucp); }
 
 ; Please copy any additions and changes to the following compatability tables:
 ; sys/ia64/ia32/syscalls.master  (take a best guess)
diff --git a/sys/powerpc/aim/machdep.c b/sys/powerpc/aim/machdep.c
index a14d966..ffb5070 100644
--- a/sys/powerpc/aim/machdep.c
+++ b/sys/powerpc/aim/machdep.c
@@ -638,6 +638,20 @@ freebsd4_sigreturn(struct thread *td, struct freebsd4_sigreturn_args *uap)
 }
 #endif
 
+int
+get_mcontext(struct thread *td, mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
+int
+set_mcontext(struct thread *td, const mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
 void
 cpu_boot(int howto)
 {
diff --git a/sys/powerpc/powerpc/machdep.c b/sys/powerpc/powerpc/machdep.c
index a14d966..ffb5070 100644
--- a/sys/powerpc/powerpc/machdep.c
+++ b/sys/powerpc/powerpc/machdep.c
@@ -638,6 +638,20 @@ freebsd4_sigreturn(struct thread *td, struct freebsd4_sigreturn_args *uap)
 }
 #endif
 
+int
+get_mcontext(struct thread *td, mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
+int
+set_mcontext(struct thread *td, const mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
 void
 cpu_boot(int howto)
 {
diff --git a/sys/sparc64/sparc64/machdep.c b/sys/sparc64/sparc64/machdep.c
index 116741b..84cf92a 100644
--- a/sys/sparc64/sparc64/machdep.c
+++ b/sys/sparc64/sparc64/machdep.c
@@ -504,6 +504,20 @@ freebsd4_sigreturn(struct thread *td, struct freebsd4_sigreturn_args *uap)
 }
 #endif
 
+int
+get_mcontext(struct thread *td, mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
+int
+set_mcontext(struct thread *td, const mcontext_t *mcp)
+{
+
+	return (ENOSYS);
+}
+
 /*
  * Exit the kernel and execute a firmware call that will not return, as
  * specified by the arguments.
diff --git a/sys/sys/ucontext.h b/sys/sys/ucontext.h
index dcce16e..1ea01d5 100644
--- a/sys/sys/ucontext.h
+++ b/sys/sys/ucontext.h
@@ -79,6 +79,14 @@ int	swapcontext(ucontext_t *, const ucontext_t *);
 
 __END_DECLS
 
+#else /* _KERNEL */
+
+struct thread;
+
+/* Machine-dependent functions: */
+int	get_mcontext(struct thread *td, mcontext_t *mcp);
+int	set_mcontext(struct thread *td, const mcontext_t *mcp);
+
 #endif /* !_KERNEL */
 
 #endif /* !_SYS_UCONTEXT_H_ */