nios2: System calls handling

This patch adds support for system calls from userspaces. It uses the
asm-generic/unistd.h definitions with architecture spcific syscall.
The sys_call_table is just an array defined in a C file and it contains
pointers to the syscall functions.

Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/include/asm/syscall.h

@@ -0,0 +1,138 @@
+/*
+ * Copyright Altera Corporation (C) <2014>. All rights reserved
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __ASM_NIOS2_SYSCALL_H__
+#define __ASM_NIOS2_SYSCALL_H__
+
+#include <linux/err.h>
+#include <linux/sched.h>
+
+static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
+{
+	return regs->r2;
+}
+
+static inline void syscall_rollback(struct task_struct *task,
+				struct pt_regs *regs)
+{
+	regs->r2 = regs->orig_r2;
+	regs->r7 = regs->orig_r7;
+}
+
+static inline long syscall_get_error(struct task_struct *task,
+				struct pt_regs *regs)
+{
+	return regs->r7 ? regs->r2 : 0;
+}
+
+static inline long syscall_get_return_value(struct task_struct *task,
+	struct pt_regs *regs)
+{
+	return regs->r2;
+}
+
+static inline void syscall_set_return_value(struct task_struct *task,
+	struct pt_regs *regs, int error, long val)
+{
+	if (error) {
+		/* error < 0, but nios2 uses > 0 return value */
+		regs->r2 = -error;
+		regs->r7 = 1;
+	} else {
+		regs->r2 = val;
+		regs->r7 = 0;
+	}
+}
+
+static inline void syscall_get_arguments(struct task_struct *task,
+	struct pt_regs *regs, unsigned int i, unsigned int n,
+	unsigned long *args)
+{
+	BUG_ON(i + n > 6);
+
+	switch (i) {
+	case 0:
+		if (!n--)
+			break;
+		*args++ = regs->r4;
+	case 1:
+		if (!n--)
+			break;
+		*args++ = regs->r5;
+	case 2:
+		if (!n--)
+			break;
+		*args++ = regs->r6;
+	case 3:
+		if (!n--)
+			break;
+		*args++ = regs->r7;
+	case 4:
+		if (!n--)
+			break;
+		*args++ = regs->r8;
+	case 5:
+		if (!n--)
+			break;
+		*args++ = regs->r9;
+	case 6:
+		if (!n--)
+			break;
+	default:
+		BUG();
+	}
+}
+
+static inline void syscall_set_arguments(struct task_struct *task,
+	struct pt_regs *regs, unsigned int i, unsigned int n,
+	const unsigned long *args)
+{
+	BUG_ON(i + n > 6);
+
+	switch (i) {
+	case 0:
+		if (!n--)
+			break;
+		regs->r4 = *args++;
+	case 1:
+		if (!n--)
+			break;
+		regs->r5 = *args++;
+	case 2:
+		if (!n--)
+			break;
+		regs->r6 = *args++;
+	case 3:
+		if (!n--)
+			break;
+		regs->r7 = *args++;
+	case 4:
+		if (!n--)
+			break;
+		regs->r8 = *args++;
+	case 5:
+		if (!n--)
+			break;
+		regs->r9 = *args++;
+	case 6:
+		if (!n)
+			break;
+	default:
+		BUG();
+	}
+}
+
+#endif