/*
 * Handle unaligned accesses by emulation.
 *
 * 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.
 *
 * Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
 * Copyright (C) 1999 Silicon Graphics, Inc.
 *
 * This file contains exception handler for address error exception with the
 * special capability to execute faulting instructions in software.  The
 * handler does not try to handle the case when the program counter points
 * to an address not aligned to a word boundary.
 *
 * Putting data to unaligned addresses is a bad practice even on Intel where
 * only the performance is affected.  Much worse is that such code is non-
 * portable.  Due to several programs that die on MIPS due to alignment
 * problems I decided to implement this handler anyway though I originally
 * didn't intend to do this at all for user code.
 *
 * For now I enable fixing of address errors by default to make life easier.
 * I however intend to disable this somewhen in the future when the alignment
 * problems with user programs have been fixed.  For programmers this is the
 * right way to go.
 *
 * Fixing address errors is a per process option.  The option is inherited
 * across fork(2) and execve(2) calls.  If you really want to use the
 * option in your user programs - I discourage the use of the software
 * emulation strongly - use the following code in your userland stuff:
 *
 * #include <sys/sysmips.h>
 *
 * ...
 * sysmips(MIPS_FIXADE, x);
 * ...
 *
 * The argument x is 0 for disabling software emulation, enabled otherwise.
 *
 * Below a little program to play around with this feature.
 *
 * #include <stdio.h>
 * #include <sys/sysmips.h>
 *
 * struct foo {
 *         unsigned char bar[8];
 * };
 *
 * main(int argc, char *argv[])
 * {
 *         struct foo x = {0, 1, 2, 3, 4, 5, 6, 7};
 *         unsigned int *p = (unsigned int *) (x.bar + 3);
 *         int i;
 *
 *         if (argc > 1)
 *                 sysmips(MIPS_FIXADE, atoi(argv[1]));
 *
 *         printf("*p = %08lx\n", *p);
 *
 *         *p = 0xdeadface;
 *
 *         for(i = 0; i <= 7; i++)
 *         printf("%02x ", x.bar[i]);
 *         printf("\n");
 * }
 *
 * Coprocessor loads are not supported; I think this case is unimportant
 * in the practice.
 *
 * TODO: Handle ndc (attempted store to doubleword in uncached memory)
 *       exception for the R6000.
 *       A store crossing a page boundary might be executed only partially.
 *       Undo the partial store in this case.
 */
#include <linux/mm.h>
#include <linux/signal.h>
#include <linux/smp.h>
#include <linux/sched.h>
#include <linux/debugfs.h>
#include <linux/perf_event.h>

#include <asm/asm.h>
#include <asm/branch.h>
#include <asm/byteorder.h>
#include <asm/cop2.h>
#include <asm/inst.h>
#include <asm/uaccess.h>
#include <asm/system.h>

#define STR(x)  __STR(x)
#define __STR(x)  #x

enum {
        UNALIGNED_ACTION_QUIET,
        UNALIGNED_ACTION_SIGNAL,
        UNALIGNED_ACTION_SHOW,
};
#ifdef CONFIG_DEBUG_FS
static u32 unaligned_instructions;
static u32 unaligned_action;
#else
#define unaligned_action UNALIGNED_ACTION_QUIET
#endif
extern void show_registers(struct pt_regs *regs);

static void emulate_load_store_insn(struct pt_regs *regs,
        void __user *addr, unsigned int __user *pc)
{
        union mips_instruction insn;
        unsigned long value;
        unsigned int res;

        perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, 0);

        /*
         * This load never faults.
         */
        __get_user(insn.word, pc);

        switch (insn.i_format.opcode) {
        /*
         * These are instructions that a compiler doesn't generate.  We
         * can assume therefore that the code is MIPS-aware and
         * really buggy.  Emulating these instructions would break the
         * semantics anyway.
         */
        case ll_op:
        case lld_op:
        case sc_op:
        case scd_op:

        /*
         * For these instructions the only way to create an address
         * error is an attempted access to kernel/supervisor address
         * space.
         */
        case ldl_op:
        case ldr_op:
        case lwl_op:
        case lwr_op:
        case sdl_op:
        case sdr_op:
        case swl_op:
        case swr_op:
        case lb_op:
        case lbu_op:
        case sb_op:
                goto sigbus;

        /*
         * The remaining opcodes are the ones that are really of interest.
         */
        case lh_op:
                if (!access_ok(VERIFY_READ, addr, 2))
                        goto sigbus;

                __asm__ __volatile__ (".set\tnoat\n"
#ifdef __BIG_ENDIAN
                        "1:\tlb\t%0, 0(%2)\n"
                        "2:\tlbu\t$1, 1(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tlb\t%0, 1(%2)\n"
                        "2:\tlbu\t$1, 0(%2)\n\t"
#endif
                        "sll\t%0, 0x8\n\t"
                        "or\t%0, $1\n\t"
                        "li\t%1, 0\n"
                        "3:\t.set\tat\n\t"
                        ".section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%1, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=&r" (value), "=r" (res)
                        : "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                regs->regs[insn.i_format.rt] = value;
                break;

        case lw_op:
                if (!access_ok(VERIFY_READ, addr, 4))
                        goto sigbus;

                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        "1:\tlwl\t%0, (%2)\n"
                        "2:\tlwr\t%0, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tlwl\t%0, 3(%2)\n"
                        "2:\tlwr\t%0, (%2)\n\t"
#endif
                        "li\t%1, 0\n"
                        "3:\t.section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%1, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=&r" (value), "=r" (res)
                        : "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                regs->regs[insn.i_format.rt] = value;
                break;

        case lhu_op:
                if (!access_ok(VERIFY_READ, addr, 2))
                        goto sigbus;

                __asm__ __volatile__ (
                        ".set\tnoat\n"
#ifdef __BIG_ENDIAN
                        "1:\tlbu\t%0, 0(%2)\n"
                        "2:\tlbu\t$1, 1(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tlbu\t%0, 1(%2)\n"
                        "2:\tlbu\t$1, 0(%2)\n\t"
#endif
                        "sll\t%0, 0x8\n\t"
                        "or\t%0, $1\n\t"
                        "li\t%1, 0\n"
                        "3:\t.set\tat\n\t"
                        ".section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%1, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=&r" (value), "=r" (res)
                        : "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                regs->regs[insn.i_format.rt] = value;
                break;

        case lwu_op:
#ifdef CONFIG_64BIT
                /*
                 * A 32-bit kernel might be running on a 64-bit processor.  But
                 * if we're on a 32-bit processor and an i-cache incoherency
                 * or race makes us see a 64-bit instruction here the sdl/sdr
                 * would blow up, so for now we don't handle unaligned 64-bit
                 * instructions on 32-bit kernels.
                 */
                if (!access_ok(VERIFY_READ, addr, 4))
                        goto sigbus;

                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        "1:\tlwl\t%0, (%2)\n"
                        "2:\tlwr\t%0, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tlwl\t%0, 3(%2)\n"
                        "2:\tlwr\t%0, (%2)\n\t"
#endif
                        "dsll\t%0, %0, 32\n\t"
                        "dsrl\t%0, %0, 32\n\t"
                        "li\t%1, 0\n"
                        "3:\t.section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%1, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=&r" (value), "=r" (res)
                        : "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                regs->regs[insn.i_format.rt] = value;
                break;
#endif /* CONFIG_64BIT */

                /* Cannot handle 64-bit instructions in 32-bit kernel */
                goto sigill;

        case ld_op:
#ifdef CONFIG_64BIT
                /*
                 * A 32-bit kernel might be running on a 64-bit processor.  But
                 * if we're on a 32-bit processor and an i-cache incoherency
                 * or race makes us see a 64-bit instruction here the sdl/sdr
                 * would blow up, so for now we don't handle unaligned 64-bit
                 * instructions on 32-bit kernels.
                 */
                if (!access_ok(VERIFY_READ, addr, 8))
                        goto sigbus;

                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        "1:\tldl\t%0, (%2)\n"
                        "2:\tldr\t%0, 7(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tldl\t%0, 7(%2)\n"
                        "2:\tldr\t%0, (%2)\n\t"
#endif
                        "li\t%1, 0\n"
                        "3:\t.section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%1, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=&r" (value), "=r" (res)
                        : "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                regs->regs[insn.i_format.rt] = value;
                break;
#endif /* CONFIG_64BIT */

                /* Cannot handle 64-bit instructions in 32-bit kernel */
                goto sigill;

        case sh_op:
                if (!access_ok(VERIFY_WRITE, addr, 2))
                        goto sigbus;

                value = regs->regs[insn.i_format.rt];
                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        ".set\tnoat\n"
                        "1:\tsb\t%1, 1(%2)\n\t"
                        "srl\t$1, %1, 0x8\n"
                        "2:\tsb\t$1, 0(%2)\n\t"
                        ".set\tat\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        ".set\tnoat\n"
                        "1:\tsb\t%1, 0(%2)\n\t"
                        "srl\t$1,%1, 0x8\n"
                        "2:\tsb\t$1, 1(%2)\n\t"
                        ".set\tat\n\t"
#endif
                        "li\t%0, 0\n"
                        "3:\n\t"
                        ".section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%0, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                        : "=r" (res)
                        : "r" (value), "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                break;

        case sw_op:
                if (!access_ok(VERIFY_WRITE, addr, 4))
                        goto sigbus;

                value = regs->regs[insn.i_format.rt];
                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        "1:\tswl\t%1,(%2)\n"
                        "2:\tswr\t%1, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tswl\t%1, 3(%2)\n"
                        "2:\tswr\t%1, (%2)\n\t"
#endif
                        "li\t%0, 0\n"
                        "3:\n\t"
                        ".section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%0, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                : "=r" (res)
                : "r" (value), "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                break;

        case sd_op:
#ifdef CONFIG_64BIT
                /*
                 * A 32-bit kernel might be running on a 64-bit processor.  But
                 * if we're on a 32-bit processor and an i-cache incoherency
                 * or race makes us see a 64-bit instruction here the sdl/sdr
                 * would blow up, so for now we don't handle unaligned 64-bit
                 * instructions on 32-bit kernels.
                 */
                if (!access_ok(VERIFY_WRITE, addr, 8))
                        goto sigbus;

                value = regs->regs[insn.i_format.rt];
                __asm__ __volatile__ (
#ifdef __BIG_ENDIAN
                        "1:\tsdl\t%1,(%2)\n"
                        "2:\tsdr\t%1, 7(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
                        "1:\tsdl\t%1, 7(%2)\n"
                        "2:\tsdr\t%1, (%2)\n\t"
#endif
                        "li\t%0, 0\n"
                        "3:\n\t"
                        ".section\t.fixup,\"ax\"\n\t"
                        "4:\tli\t%0, %3\n\t"
                        "j\t3b\n\t"
                        ".previous\n\t"
                        ".section\t__ex_table,\"a\"\n\t"
                        STR(PTR)"\t1b, 4b\n\t"
                        STR(PTR)"\t2b, 4b\n\t"
                        ".previous"
                : "=r" (res)
                : "r" (value), "r" (addr), "i" (-EFAULT));
                if (res)
                        goto fault;
                compute_return_epc(regs);
                break;
#endif /* CONFIG_64BIT */

                /* Cannot handle 64-bit instructions in 32-bit kernel */
                goto sigill;

        case lwc1_op:
        case ldc1_op:
        case swc1_op:
        case sdc1_op:
                /*
                 * I herewith declare: this does not happen.  So send SIGBUS.
                 */
                goto sigbus;

        /*
         * COP2 is available to implementor for application specific use.
         * It's up to applications to register a notifier chain and do
         * whatever they have to do, including possible sending of signals.
         */
        case lwc2_op:
                cu2_notifier_call_chain(CU2_LWC2_OP, regs);
                break;

        case ldc2_op:
                cu2_notifier_call_chain(CU2_LDC2_OP, regs);
                break;

        case swc2_op:
                cu2_notifier_call_chain(CU2_SWC2_OP, regs);
                break;

        case sdc2_op:
                cu2_notifier_call_chain(CU2_SDC2_OP, regs);
                break;

        default:
                /*
                 * Pheeee...  We encountered an yet unknown instruction or
                 * cache coherence problem.  Die sucker, die ...
                 */
                goto sigill;
        }

#ifdef CONFIG_DEBUG_FS
        unaligned_instructions++;
#endif

        return;

fault:
        /* Did we have an exception handler installed? */
        if (fixup_exception(regs))
                return;

        die_if_kernel("Unhandled kernel unaligned access", regs);
        force_sig(SIGSEGV, current);

        return;

sigbus:
        die_if_kernel("Unhandled kernel unaligned access", regs);
        force_sig(SIGBUS, current);

        return;

sigill:
        die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
        force_sig(SIGILL, current);
}

asmlinkage void do_ade(struct pt_regs *regs)
{
        unsigned int __user *pc;
        mm_segment_t seg;

        perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
                        1, regs, regs->cp0_badvaddr);
        /*
         * Did we catch a fault trying to load an instruction?
         * Or are we running in MIPS16 mode?
         */
        if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
                goto sigbus;

        pc = (unsigned int __user *) exception_epc(regs);
        if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
                goto sigbus;
        if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
                goto sigbus;
        else if (unaligned_action == UNALIGNED_ACTION_SHOW)
                show_registers(regs);

        /*
         * Do branch emulation only if we didn't forward the exception.
         * This is all so but ugly ...
         */
        seg = get_fs();
        if (!user_mode(regs))
                set_fs(KERNEL_DS);
        emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc);
        set_fs(seg);

        return;

sigbus:
        die_if_kernel("Kernel unaligned instruction access", regs);
        force_sig(SIGBUS, current);

        /*
         * XXX On return from the signal handler we should advance the epc
         */
}

#ifdef CONFIG_DEBUG_FS
extern struct dentry *mips_debugfs_dir;
static int __init debugfs_unaligned(void)
{
        struct dentry *d;

        if (!mips_debugfs_dir)
                return -ENODEV;
        d = debugfs_create_u32("unaligned_instructions", S_IRUGO,
                               mips_debugfs_dir, &unaligned_instructions);
        if (!d)
                return -ENOMEM;
        d = debugfs_create_u32("unaligned_action", S_IRUGO | S_IWUSR,
                               mips_debugfs_dir, &unaligned_action);
        if (!d)
                return -ENOMEM;
        return 0;
}
__initcall(debugfs_unaligned);
#endif