/*
 *  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 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;
        s16 imm16;
        unsigned int fault;

        /* back up one instruction */
        fp->ea -= 4;

        if (fixup_exception(fp)) {
                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);
                        break;
                case INST_STH:
                        val = get_reg_val(fp, b);
                        d1 = val >> 8;
                        d0 = val >> 0;
                        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));
                        }
                        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);
                        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));
                        }
                        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);
                        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) {
                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;
        }

        /*
         * 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);