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

1 files changed, 134 insertions, 0 deletions

diff --git a/sys/kern/kern_context.c b/sys/kern/kern_context.c
new file mode 100644
index 000000000000..1cc0eac8da71
--- /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);
+}