nios2: Exception handling

This patch contains the exception entry code (kernel/entry.S) and
misaligned exception.
Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/kernel/misaligned.c

+/*
+ *  linux/arch/nios2/kernel/misaligned.c
+ *
+ *  basic emulation for mis-aligned accesses on the NIOS II cpu
+ *  modelled after the version for arm in arm/alignment.c
+ *
+ *  Brad Parker <brad@heeltoe.com>
+ *  Copyright (C) 2010 Ambient Corporation
+ *  Copyright (c) 2010 Altera Corporation, San Jose, California, USA.
+ *  Copyright (c) 2010 Arrow Electronics, Inc.
+ *
+ * This file is subject to the terms and conditions of the GNU General
+ * Public License.  See the file COPYING in the main directory of
+ * this archive for more details.
+ */
+
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/proc_fs.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+#include <linux/seq_file.h>
+
+#include <asm/traps.h>
+#include <asm/unaligned.h>
+
+/* instructions we emulate */
+#define INST_LDHU	0x0b
+#define INST_STH	0x0d
+#define INST_LDH	0x0f
+#define INST_STW	0x15
+#define INST_LDW	0x17
+
+static unsigned long ma_user, ma_kern, ma_skipped, ma_half, ma_word;
+
+static unsigned int ma_usermode;
+#define UM_WARN		0x01
+#define UM_FIXUP	0x02
+#define UM_SIGNAL	0x04
+#define KM_WARN		0x08
+
+/* see arch/nios2/include/asm/ptrace.h */
+static u8 sys_stack_frame_reg_offset[] = {
+	/* struct pt_regs */
+	8, 9, 10, 11, 12, 13, 14, 15, 1, 2, 3, 4, 5, 6, 7, 0,
+	/* struct switch_stack */
+	16, 17, 18, 19, 20, 21, 22, 23, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+static int reg_offsets[32];
+
+static inline u32 get_reg_val(struct pt_regs *fp, int reg)
+{
+	u8 *p = ((u8 *)fp) + reg_offsets[reg];
+
+	return *(u32 *)p;
+}
+
+static inline void put_reg_val(struct pt_regs *fp, int reg, u32 val)
+{
+	u8 *p = ((u8 *)fp) + reg_offsets[reg];
+	*(u32 *)p = val;
+}
+
+/*
+ * (mis)alignment handler
+ */
+asmlinkage void handle_unaligned_c(struct pt_regs *fp, int cause)
+{
+	u32 isn, addr, val;
+	int in_kernel;
+	u8 a, b, d0, d1, d2, d3;
+	u16 imm16;
+	unsigned int fault;
+
+	/* back up one instruction */
+	fp->ea -= 4;
+
+	if (fixup_exception(fp)) {
+		ma_skipped++;
+		return;
+	}
+
+	in_kernel = !user_mode(fp);
+
+	isn = *(unsigned long *)(fp->ea);
+
+	fault = 0;
+
+	/* do fixup if in kernel or mode turned on */
+	if (in_kernel || (ma_usermode & UM_FIXUP)) {
+		/* decompose instruction */
+		a = (isn >> 27) & 0x1f;
+		b = (isn >> 22) & 0x1f;
+		imm16 = (isn >> 6) & 0xffff;
+		addr = get_reg_val(fp, a) + imm16;
+
+		/* do fixup to saved registers */
+		switch (isn & 0x3f) {
+		case INST_LDHU:
+			fault |= __get_user(d0, (u8 *)(addr+0));
+			fault |= __get_user(d1, (u8 *)(addr+1));
+			val = (d1 << 8) | d0;
+			put_reg_val(fp, b, val);
+			ma_half++;
+			break;
+		case INST_STH:
+			val = get_reg_val(fp, b);
+			d1 = val >> 8;
+			d0 = val >> 0;
+
+			pr_debug("sth: ra=%d (%08x) rb=%d (%08x), imm16 %04x addr %08x val %08x\n",
+				a, get_reg_val(fp, a),
+				b, get_reg_val(fp, b),
+				imm16, addr, val);
+
+			if (in_kernel) {
+				*(u8 *)(addr+0) = d0;
+				*(u8 *)(addr+1) = d1;
+			} else {
+				fault |= __put_user(d0, (u8 *)(addr+0));
+				fault |= __put_user(d1, (u8 *)(addr+1));
+			}
+			ma_half++;
+			break;
+		case INST_LDH:
+			fault |= __get_user(d0, (u8 *)(addr+0));
+			fault |= __get_user(d1, (u8 *)(addr+1));
+			val = (short)((d1 << 8) | d0);
+			put_reg_val(fp, b, val);
+			ma_half++;
+			break;
+		case INST_STW:
+			val = get_reg_val(fp, b);
+			d3 = val >> 24;
+			d2 = val >> 16;
+			d1 = val >> 8;
+			d0 = val >> 0;
+			if (in_kernel) {
+				*(u8 *)(addr+0) = d0;
+				*(u8 *)(addr+1) = d1;
+				*(u8 *)(addr+2) = d2;
+				*(u8 *)(addr+3) = d3;
+			} else {
+				fault |= __put_user(d0, (u8 *)(addr+0));
+				fault |= __put_user(d1, (u8 *)(addr+1));
+				fault |= __put_user(d2, (u8 *)(addr+2));
+				fault |= __put_user(d3, (u8 *)(addr+3));
+			}
+			ma_word++;
+			break;
+		case INST_LDW:
+			fault |= __get_user(d0, (u8 *)(addr+0));
+			fault |= __get_user(d1, (u8 *)(addr+1));
+			fault |= __get_user(d2, (u8 *)(addr+2));
+			fault |= __get_user(d3, (u8 *)(addr+3));
+			val = (d3 << 24) | (d2 << 16) | (d1 << 8) | d0;
+			put_reg_val(fp, b, val);
+			ma_word++;
+			break;
+		}
+	}
+
+	addr = RDCTL(CTL_BADADDR);
+	cause >>= 2;
+
+	if (fault) {
+		if (in_kernel) {
+			pr_err("fault during kernel misaligned fixup @ %#lx; addr 0x%08x; isn=0x%08x\n",
+				fp->ea, (unsigned int)addr,
+				(unsigned int)isn);
+		} else {
+			pr_err("fault during user misaligned fixup @ %#lx; isn=%08x addr=0x%08x sp=0x%08lx pid=%d\n",
+				fp->ea,
+				(unsigned int)isn, addr, fp->sp,
+				current->pid);
+
+			_exception(SIGSEGV, fp, SEGV_MAPERR, fp->ea);
+			return;
+		}
+	}
+
+	/*
+	 * kernel mode -
+	 *  note exception and skip bad instruction (return)
+	 */
+	if (in_kernel) {
+		ma_kern++;
+		fp->ea += 4;
+
+		if (ma_usermode & KM_WARN) {
+			pr_err("kernel unaligned access @ %#lx; BADADDR 0x%08x; cause=%d, isn=0x%08x\n",
+				fp->ea,
+				(unsigned int)addr, cause,
+				(unsigned int)isn);
+			/* show_regs(fp); */
+		}
+
+		return;
+	}
+
+	ma_user++;
+
+	/*
+	 * user mode -
+	 *  possibly warn,
+	 *  possibly send SIGBUS signal to process
+	 */
+	if (ma_usermode & UM_WARN) {
+		pr_err("user unaligned access @ %#lx; isn=0x%08lx ea=0x%08lx ra=0x%08lx sp=0x%08lx\n",
+			(unsigned long)addr, (unsigned long)isn,
+			fp->ea, fp->ra, fp->sp);
+	}
+
+	if (ma_usermode & UM_SIGNAL)
+		_exception(SIGBUS, fp, BUS_ADRALN, fp->ea);
+	else
+		fp->ea += 4;	/* else advance */
+}
+
+static void __init misaligned_calc_reg_offsets(void)
+{
+	int i, r, offset;
+
+	/* pre-calc offsets of registers on sys call stack frame */
+	offset = 0;
+
+	/* struct pt_regs */
+	for (i = 0; i < 16; i++) {
+		r = sys_stack_frame_reg_offset[i];
+		reg_offsets[r] = offset;
+		offset += 4;
+	}
+
+	/* struct switch_stack */
+	offset = -sizeof(struct switch_stack);
+	for (i = 16; i < 32; i++) {
+		r = sys_stack_frame_reg_offset[i];
+		reg_offsets[r] = offset;
+		offset += 4;
+	}
+}
+
+
+static int __init misaligned_init(void)
+{
+	/* default mode - silent fix */
+	ma_usermode = UM_FIXUP | KM_WARN;
+
+	misaligned_calc_reg_offsets();
+
+	return 0;
+}
+
+fs_initcall(misaligned_init);