/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 *
 * A code-rewriter that enables instruction single-stepping.
 */

#include <linux/smp.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/thread_info.h>
#include <linux/uaccess.h>
#include <linux/mman.h>
#include <linux/types.h>
#include <linux/err.h>
#include <linux/prctl.h>
#include <asm/cacheflush.h>
#include <asm/traps.h>
#include <linux/uaccess.h>
#include <asm/unaligned.h>
#include <arch/abi.h>
#include <arch/spr_def.h>
#include <arch/opcode.h>


#ifndef __tilegx__   /* Hardware support for single step unavailable. */

#define signExtend17(val) sign_extend((val), 17)
#define TILE_X1_MASK (0xffffffffULL << 31)

enum mem_op {
        MEMOP_NONE,
        MEMOP_LOAD,
        MEMOP_STORE,
        MEMOP_LOAD_POSTINCR,
        MEMOP_STORE_POSTINCR
};

static inline tilepro_bundle_bits set_BrOff_X1(tilepro_bundle_bits n,
        s32 offset)
{
        tilepro_bundle_bits result;

        /* mask out the old offset */
        tilepro_bundle_bits mask = create_BrOff_X1(-1);
        result = n & (~mask);

        /* or in the new offset */
        result |= create_BrOff_X1(offset);

        return result;
}

static inline tilepro_bundle_bits move_X1(tilepro_bundle_bits n, int dest,
        int src)
{
        tilepro_bundle_bits result;
        tilepro_bundle_bits op;

        result = n & (~TILE_X1_MASK);

        op = create_Opcode_X1(SPECIAL_0_OPCODE_X1) |
                create_RRROpcodeExtension_X1(OR_SPECIAL_0_OPCODE_X1) |
                create_Dest_X1(dest) |
                create_SrcB_X1(TREG_ZERO) |
                create_SrcA_X1(src) ;

        result |= op;
        return result;
}

static inline tilepro_bundle_bits nop_X1(tilepro_bundle_bits n)
{
        return move_X1(n, TREG_ZERO, TREG_ZERO);
}

static inline tilepro_bundle_bits addi_X1(
        tilepro_bundle_bits n, int dest, int src, int imm)
{
        n &= ~TILE_X1_MASK;

        n |=  (create_SrcA_X1(src) |
               create_Dest_X1(dest) |
               create_Imm8_X1(imm) |
               create_S_X1(0) |
               create_Opcode_X1(IMM_0_OPCODE_X1) |
               create_ImmOpcodeExtension_X1(ADDI_IMM_0_OPCODE_X1));

        return n;
}

static tilepro_bundle_bits rewrite_load_store_unaligned(
        struct single_step_state *state,
        tilepro_bundle_bits bundle,
        struct pt_regs *regs,
        enum mem_op mem_op,
        int size, int sign_ext)
{
        unsigned char __user *addr;
        int val_reg, addr_reg, err, val;
        int align_ctl;

        align_ctl = unaligned_fixup;
        switch (task_thread_info(current)->align_ctl) {
        case PR_UNALIGN_NOPRINT:
                align_ctl = 1;
                break;
        case PR_UNALIGN_SIGBUS:
                align_ctl = 0;
                break;
        }

        /* Get address and value registers */
        if (bundle & TILEPRO_BUNDLE_Y_ENCODING_MASK) {
                addr_reg = get_SrcA_Y2(bundle);
                val_reg = get_SrcBDest_Y2(bundle);
        } else if (mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR) {
                addr_reg = get_SrcA_X1(bundle);
                val_reg  = get_Dest_X1(bundle);
        } else {
                addr_reg = get_SrcA_X1(bundle);
                val_reg  = get_SrcB_X1(bundle);
        }

        /*
         * If registers are not GPRs, don't try to handle it.
         *
         * FIXME: we could handle non-GPR loads by getting the real value
         * from memory, writing it to the single step buffer, using a
         * temp_reg to hold a pointer to that memory, then executing that
         * instruction and resetting temp_reg.  For non-GPR stores, it's a
         * little trickier; we could use the single step buffer for that
         * too, but we'd have to add some more state bits so that we could
         * call back in here to copy that value to the real target.  For
         * now, we just handle the simple case.
         */
        if ((val_reg >= PTREGS_NR_GPRS &&
             (val_reg != TREG_ZERO ||
              mem_op == MEMOP_LOAD ||
              mem_op == MEMOP_LOAD_POSTINCR)) ||
            addr_reg >= PTREGS_NR_GPRS)
                return bundle;

        /* If it's aligned, don't handle it specially */
        addr = (void __user *)regs->regs[addr_reg];
        if (((unsigned long)addr % size) == 0)
                return bundle;

        /*
         * Return SIGBUS with the unaligned address, if requested.
         * Note that we return SIGBUS even for completely invalid addresses
         * as long as they are in fact unaligned; this matches what the
         * tilepro hardware would be doing, if it could provide us with the
         * actual bad address in an SPR, which it doesn't.
         */
        if (align_ctl == 0) {
                siginfo_t info = {
                        .si_signo = SIGBUS,
                        .si_code = BUS_ADRALN,
                        .si_addr = addr
                };
                trace_unhandled_signal("unaligned trap", regs,
                                       (unsigned long)addr, SIGBUS);
                force_sig_info(info.si_signo, &info, current);
                return (tilepro_bundle_bits) 0;
        }

        /* Handle unaligned load/store */
        if (mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR) {
                unsigned short val_16;
                switch (size) {
                case 2:
                        err = copy_from_user(&val_16, addr, sizeof(val_16));
                        val = sign_ext ? ((short)val_16) : val_16;
                        break;
                case 4:
                        err = copy_from_user(&val, addr, sizeof(val));
                        break;
                default:
                        BUG();
                }
                if (err == 0) {
                        state->update_reg = val_reg;
                        state->update_value = val;
                        state->update = 1;
                }
        } else {
                unsigned short val_16;
                val = (val_reg == TREG_ZERO) ? 0 : regs->regs[val_reg];
                switch (size) {
                case 2:
                        val_16 = val;
                        err = copy_to_user(addr, &val_16, sizeof(val_16));
                        break;
                case 4:
                        err = copy_to_user(addr, &val, sizeof(val));
                        break;
                default:
                        BUG();
                }
        }

        if (err) {
                siginfo_t info = {
                        .si_signo = SIGBUS,
                        .si_code = BUS_ADRALN,
                        .si_addr = addr
                };
                trace_unhandled_signal("bad address for unaligned fixup", regs,
                                       (unsigned long)addr, SIGBUS);
                force_sig_info(info.si_signo, &info, current);
                return (tilepro_bundle_bits) 0;
        }

        if (unaligned_printk || unaligned_fixup_count == 0) {
                pr_info("Process %d/%s: PC %#lx: Fixup of unaligned %s at %#lx\n",
                        current->pid, current->comm, regs->pc,
                        mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR ?
                        "load" : "store",
                        (unsigned long)addr);
                if (!unaligned_printk) {
#define P pr_info
P("\n");
P("Unaligned fixups in the kernel will slow your application considerably.\n");
P("To find them, write a \"1\" to /proc/sys/tile/unaligned_fixup/printk,\n");
P("which requests the kernel show all unaligned fixups, or write a \"0\"\n");
P("to /proc/sys/tile/unaligned_fixup/enabled, in which case each unaligned\n");
P("access will become a SIGBUS you can debug. No further warnings will be\n");
P("shown so as to avoid additional slowdown, but you can track the number\n");
P("of fixups performed via /proc/sys/tile/unaligned_fixup/count.\n");
P("Use the tile-addr2line command (see \"info addr2line\") to decode PCs.\n");
P("\n");
#undef P
                }
        }
        ++unaligned_fixup_count;

        if (bundle & TILEPRO_BUNDLE_Y_ENCODING_MASK) {
                /* Convert the Y2 instruction to a prefetch. */
                bundle &= ~(create_SrcBDest_Y2(-1) |
                            create_Opcode_Y2(-1));
                bundle |= (create_SrcBDest_Y2(TREG_ZERO) |
                           create_Opcode_Y2(LW_OPCODE_Y2));
        /* Replace the load postincr with an addi */
        } else if (mem_op == MEMOP_LOAD_POSTINCR) {
                bundle = addi_X1(bundle, addr_reg, addr_reg,
                                 get_Imm8_X1(bundle));
        /* Replace the store postincr with an addi */
        } else if (mem_op == MEMOP_STORE_POSTINCR) {
                bundle = addi_X1(bundle, addr_reg, addr_reg,
                                 get_Dest_Imm8_X1(bundle));
        } else {
                /* Convert the X1 instruction to a nop. */
                bundle &= ~(create_Opcode_X1(-1) |
                            create_UnShOpcodeExtension_X1(-1) |
                            create_UnOpcodeExtension_X1(-1));
                bundle |= (create_Opcode_X1(SHUN_0_OPCODE_X1) |
                           create_UnShOpcodeExtension_X1(
                                   UN_0_SHUN_0_OPCODE_X1) |
                           create_UnOpcodeExtension_X1(
                                   NOP_UN_0_SHUN_0_OPCODE_X1));
        }

        return bundle;
}

/*
 * Called after execve() has started the new image.  This allows us
 * to reset the info state.  Note that the the mmap'ed memory, if there
 * was any, has already been unmapped by the exec.
 */
void single_step_execve(void)
{
        struct thread_info *ti = current_thread_info();
        kfree(ti->step_state);
        ti->step_state = NULL;
}

/*
 * single_step_once() - entry point when single stepping has been triggered.
 * @regs: The machine register state
 *
 *  When we arrive at this routine via a trampoline, the single step
 *  engine copies the executing bundle to the single step buffer.
 *  If the instruction is a condition branch, then the target is
 *  reset to one past the next instruction. If the instruction
 *  sets the lr, then that is noted. If the instruction is a jump
 *  or call, then the new target pc is preserved and the current
 *  bundle instruction set to null.
 *
 *  The necessary post-single-step rewriting information is stored in
 *  single_step_state->  We use data segment values because the
 *  stack will be rewound when we run the rewritten single-stepped
 *  instruction.
 */
void single_step_once(struct pt_regs *regs)
{
        extern tilepro_bundle_bits __single_step_ill_insn;
        extern tilepro_bundle_bits __single_step_j_insn;
        extern tilepro_bundle_bits __single_step_addli_insn;
        extern tilepro_bundle_bits __single_step_auli_insn;
        struct thread_info *info = (void *)current_thread_info();
        struct single_step_state *state = info->step_state;
        int is_single_step = test_ti_thread_flag(info, TIF_SINGLESTEP);
        tilepro_bundle_bits __user *buffer, *pc;
        tilepro_bundle_bits bundle;
        int temp_reg;
        int target_reg = TREG_LR;
        int err;
        enum mem_op mem_op = MEMOP_NONE;
        int size = 0, sign_ext = 0;  /* happy compiler */
        int align_ctl;

        align_ctl = unaligned_fixup;
        switch (task_thread_info(current)->align_ctl) {
        case PR_UNALIGN_NOPRINT:
                align_ctl = 1;
                break;
        case PR_UNALIGN_SIGBUS:
                align_ctl = 0;
                break;
        }

        asm(
"    .pushsection .rodata.single_step\n"
"    .align 8\n"
"    .globl    __single_step_ill_insn\n"
"__single_step_ill_insn:\n"
"    ill\n"
"    .globl    __single_step_addli_insn\n"
"__single_step_addli_insn:\n"
"    { nop; addli r0, zero, 0 }\n"
"    .globl    __single_step_auli_insn\n"
"__single_step_auli_insn:\n"
"    { nop; auli r0, r0, 0 }\n"
"    .globl    __single_step_j_insn\n"
"__single_step_j_insn:\n"
"    j .\n"
"    .popsection\n"
        );

        /*
         * Enable interrupts here to allow touching userspace and the like.
         * The callers expect this: do_trap() already has interrupts
         * enabled, and do_work_pending() handles functions that enable
         * interrupts internally.
         */
        local_irq_enable();

        if (state == NULL) {
                /* allocate a page of writable, executable memory */
                state = kmalloc(sizeof(struct single_step_state), GFP_KERNEL);
                if (state == NULL) {
                        pr_err("Out of kernel memory trying to single-step\n");
                        return;
                }

                /* allocate a cache line of writable, executable memory */
                buffer = (void __user *) vm_mmap(NULL, 0, 64,
                                          PROT_EXEC | PROT_READ | PROT_WRITE,
                                          MAP_PRIVATE | MAP_ANONYMOUS,
                                          0);

                if (IS_ERR((void __force *)buffer)) {
                        kfree(state);
                        pr_err("Out of kernel pages trying to single-step\n");
                        return;
                }

                state->buffer = buffer;
                state->is_enabled = 0;

                info->step_state = state;

                /* Validate our stored instruction patterns */
                BUG_ON(get_Opcode_X1(__single_step_addli_insn) !=
                       ADDLI_OPCODE_X1);
                BUG_ON(get_Opcode_X1(__single_step_auli_insn) !=
                       AULI_OPCODE_X1);
                BUG_ON(get_SrcA_X1(__single_step_addli_insn) != TREG_ZERO);
                BUG_ON(get_Dest_X1(__single_step_addli_insn) != 0);
                BUG_ON(get_JOffLong_X1(__single_step_j_insn) != 0);
        }

        /*
         * If we are returning from a syscall, we still haven't hit the
         * "ill" for the swint1 instruction.  So back the PC up to be
         * pointing at the swint1, but we'll actually return directly
         * back to the "ill" so we come back in via SIGILL as if we
         * had "executed" the swint1 without ever being in kernel space.
         */
        if (regs->faultnum == INT_SWINT_1)
                regs->pc -= 8;

        pc = (tilepro_bundle_bits __user *)(regs->pc);
        if (get_user(bundle, pc) != 0) {
                pr_err("Couldn't read instruction at %p trying to step\n", pc);
                return;
        }

        /* We'll follow the instruction with 2 ill op bundles */
        state->orig_pc = (unsigned long)pc;
        state->next_pc = (unsigned long)(pc + 1);
        state->branch_next_pc = 0;
        state->update = 0;

        if (!(bundle & TILEPRO_BUNDLE_Y_ENCODING_MASK)) {
                /* two wide, check for control flow */
                int opcode = get_Opcode_X1(bundle);

                switch (opcode) {
                /* branches */
                case BRANCH_OPCODE_X1:
                {
                        s32 offset = signExtend17(get_BrOff_X1(bundle));

                        /*
                         * For branches, we use a rewriting trick to let the
                         * hardware evaluate whether the branch is taken or
                         * untaken.  We record the target offset and then
                         * rewrite the branch instruction to target 1 insn
                         * ahead if the branch is taken.  We then follow the
                         * rewritten branch with two bundles, each containing
                         * an "ill" instruction. The supervisor examines the
                         * pc after the single step code is executed, and if
                         * the pc is the first ill instruction, then the
                         * branch (if any) was not taken.  If the pc is the
                         * second ill instruction, then the branch was
                         * taken. The new pc is computed for these cases, and
                         * inserted into the registers for the thread.  If
                         * the pc is the start of the single step code, then
                         * an exception or interrupt was taken before the
                         * code started processing, and the same "original"
                         * pc is restored.  This change, different from the
                         * original implementation, has the advantage of
                         * executing a single user instruction.
                         */
                        state->branch_next_pc = (unsigned long)(pc + offset);

                        /* rewrite branch offset to go forward one bundle */
                        bundle = set_BrOff_X1(bundle, 2);
                }
                break;

                /* jumps */
                case JALB_OPCODE_X1:
                case JALF_OPCODE_X1:
                        state->update = 1;
                        state->next_pc =
                                (unsigned long) (pc + get_JOffLong_X1(bundle));
                        break;

                case JB_OPCODE_X1:
                case JF_OPCODE_X1:
                        state->next_pc =
                                (unsigned long) (pc + get_JOffLong_X1(bundle));
                        bundle = nop_X1(bundle);
                        break;

                case SPECIAL_0_OPCODE_X1:
                        switch (get_RRROpcodeExtension_X1(bundle)) {
                        /* jump-register */
                        case JALRP_SPECIAL_0_OPCODE_X1:
                        case JALR_SPECIAL_0_OPCODE_X1:
                                state->update = 1;
                                state->next_pc =
                                        regs->regs[get_SrcA_X1(bundle)];
                                break;

                        case JRP_SPECIAL_0_OPCODE_X1:
                        case JR_SPECIAL_0_OPCODE_X1:
                                state->next_pc =
                                        regs->regs[get_SrcA_X1(bundle)];
                                bundle = nop_X1(bundle);
                                break;

                        case LNK_SPECIAL_0_OPCODE_X1:
                                state->update = 1;
                                target_reg = get_Dest_X1(bundle);
                                break;

                        /* stores */
                        case SH_SPECIAL_0_OPCODE_X1:
                                mem_op = MEMOP_STORE;
                                size = 2;
                                break;

                        case SW_SPECIAL_0_OPCODE_X1:
                                mem_op = MEMOP_STORE;
                                size = 4;
                                break;
                        }
                        break;

                /* loads and iret */
                case SHUN_0_OPCODE_X1:
                        if (get_UnShOpcodeExtension_X1(bundle) ==
                            UN_0_SHUN_0_OPCODE_X1) {
                                switch (get_UnOpcodeExtension_X1(bundle)) {
                                case LH_UN_0_SHUN_0_OPCODE_X1:
                                        mem_op = MEMOP_LOAD;
                                        size = 2;
                                        sign_ext = 1;
                                        break;

                                case LH_U_UN_0_SHUN_0_OPCODE_X1:
                                        mem_op = MEMOP_LOAD;
                                        size = 2;
                                        sign_ext = 0;
                                        break;

                                case LW_UN_0_SHUN_0_OPCODE_X1:
                                        mem_op = MEMOP_LOAD;
                                        size = 4;
                                        break;

                                case IRET_UN_0_SHUN_0_OPCODE_X1:
                                {
                                        unsigned long ex0_0 = __insn_mfspr(
                                                SPR_EX_CONTEXT_0_0);
                                        unsigned long ex0_1 = __insn_mfspr(
                                                SPR_EX_CONTEXT_0_1);
                                        /*
                                         * Special-case it if we're iret'ing
                                         * to PL0 again.  Otherwise just let
                                         * it run and it will generate SIGILL.
                                         */
                                        if (EX1_PL(ex0_1) == USER_PL) {
                                                state->next_pc = ex0_0;
                                                regs->ex1 = ex0_1;
                                                bundle = nop_X1(bundle);
                                        }
                                }
                                }
                        }
                        break;

                /* postincrement operations */
                case IMM_0_OPCODE_X1:
                        switch (get_ImmOpcodeExtension_X1(bundle)) {
                        case LWADD_IMM_0_OPCODE_X1:
                                mem_op = MEMOP_LOAD_POSTINCR;
                                size = 4;
                                break;

                        case LHADD_IMM_0_OPCODE_X1:
                                mem_op = MEMOP_LOAD_POSTINCR;
                                size = 2;
                                sign_ext = 1;
                                break;

                        case LHADD_U_IMM_0_OPCODE_X1:
                                mem_op = MEMOP_LOAD_POSTINCR;
                                size = 2;
                                sign_ext = 0;
                                break;

                        case SWADD_IMM_0_OPCODE_X1:
                                mem_op = MEMOP_STORE_POSTINCR;
                                size = 4;
                                break;

                        case SHADD_IMM_0_OPCODE_X1:
                                mem_op = MEMOP_STORE_POSTINCR;
                                size = 2;
                                break;

                        default:
                                break;
                        }
                        break;
                }

                if (state->update) {
                        /*
                         * Get an available register.  We start with a
                         * bitmask with 1's for available registers.
                         * We truncate to the low 32 registers since
                         * we are guaranteed to have set bits in the
                         * low 32 bits, then use ctz to pick the first.
                         */
                        u32 mask = (u32) ~((1ULL << get_Dest_X0(bundle)) |
                                           (1ULL << get_SrcA_X0(bundle)) |
                                           (1ULL << get_SrcB_X0(bundle)) |
                                           (1ULL << target_reg));
                        temp_reg = __builtin_ctz(mask);
                        state->update_reg = temp_reg;
                        state->update_value = regs->regs[temp_reg];
                        regs->regs[temp_reg] = (unsigned long) (pc+1);
                        regs->flags |= PT_FLAGS_RESTORE_REGS;
                        bundle = move_X1(bundle, target_reg, temp_reg);
                }
        } else {
                int opcode = get_Opcode_Y2(bundle);

                switch (opcode) {
                /* loads */
                case LH_OPCODE_Y2:
                        mem_op = MEMOP_LOAD;
                        size = 2;
                        sign_ext = 1;
                        break;

                case LH_U_OPCODE_Y2:
                        mem_op = MEMOP_LOAD;
                        size = 2;
                        sign_ext = 0;
                        break;

                case LW_OPCODE_Y2:
                        mem_op = MEMOP_LOAD;
                        size = 4;
                        break;

                /* stores */
                case SH_OPCODE_Y2:
                        mem_op = MEMOP_STORE;
                        size = 2;
                        break;

                case SW_OPCODE_Y2:
                        mem_op = MEMOP_STORE;
                        size = 4;
                        break;
                }
        }

        /*
         * Check if we need to rewrite an unaligned load/store.
         * Returning zero is a special value meaning we generated a signal.
         */
        if (mem_op != MEMOP_NONE && align_ctl >= 0) {
                bundle = rewrite_load_store_unaligned(state, bundle, regs,
                                                      mem_op, size, sign_ext);
                if (bundle == 0)
                        return;
        }

        /* write the bundle to our execution area */
        buffer = state->buffer;
        err = __put_user(bundle, buffer++);

        /*
         * If we're really single-stepping, we take an INT_ILL after.
         * If we're just handling an unaligned access, we can just
         * jump directly back to where we were in user code.
         */
        if (is_single_step) {
                err |= __put_user(__single_step_ill_insn, buffer++);
                err |= __put_user(__single_step_ill_insn, buffer++);
        } else {
                long delta;

                if (state->update) {
                        /* We have some state to update; do it inline */
                        int ha16;
                        bundle = __single_step_addli_insn;
                        bundle |= create_Dest_X1(state->update_reg);
                        bundle |= create_Imm16_X1(state->update_value);
                        err |= __put_user(bundle, buffer++);
                        bundle = __single_step_auli_insn;
                        bundle |= create_Dest_X1(state->update_reg);
                        bundle |= create_SrcA_X1(state->update_reg);
                        ha16 = (state->update_value + 0x8000) >> 16;
                        bundle |= create_Imm16_X1(ha16);
                        err |= __put_user(bundle, buffer++);
                        state->update = 0;
                }

                /* End with a jump back to the next instruction */
                delta = ((regs->pc + TILEPRO_BUNDLE_SIZE_IN_BYTES) -
                        (unsigned long)buffer) >>
                        TILEPRO_LOG2_BUNDLE_ALIGNMENT_IN_BYTES;
                bundle = __single_step_j_insn;
                bundle |= create_JOffLong_X1(delta);
                err |= __put_user(bundle, buffer++);
        }

        if (err) {
                pr_err("Fault when writing to single-step buffer\n");
                return;
        }

        /*
         * Flush the buffer.
         * We do a local flush only, since this is a thread-specific buffer.
         */
        __flush_icache_range((unsigned long)state->buffer,
                             (unsigned long)buffer);

        /* Indicate enabled */
        state->is_enabled = is_single_step;
        regs->pc = (unsigned long)state->buffer;

        /* Fault immediately if we are coming back from a syscall. */
        if (regs->faultnum == INT_SWINT_1)
                regs->pc += 8;
}

#else

static DEFINE_PER_CPU(unsigned long, ss_saved_pc);


/*
 * Called directly on the occasion of an interrupt.
 *
 * If the process doesn't have single step set, then we use this as an
 * opportunity to turn single step off.
 *
 * It has been mentioned that we could conditionally turn off single stepping
 * on each entry into the kernel and rely on single_step_once to turn it
 * on for the processes that matter (as we already do), but this
 * implementation is somewhat more efficient in that we muck with registers
 * once on a bum interrupt rather than on every entry into the kernel.
 *
 * If SINGLE_STEP_CONTROL_K has CANCELED set, then an interrupt occurred,
 * so we have to run through this process again before we can say that an
 * instruction has executed.
 *
 * swint will set CANCELED, but it's a legitimate instruction.  Fortunately
 * it changes the PC.  If it hasn't changed, then we know that the interrupt
 * wasn't generated by swint and we'll need to run this process again before
 * we can say an instruction has executed.
 *
 * If either CANCELED == 0 or the PC's changed, we send out SIGTRAPs and get
 * on with our lives.
 */

void gx_singlestep_handle(struct pt_regs *regs, int fault_num)
{
        unsigned long *ss_pc = this_cpu_ptr(&ss_saved_pc);
        struct thread_info *info = (void *)current_thread_info();
        int is_single_step = test_ti_thread_flag(info, TIF_SINGLESTEP);
        unsigned long control = __insn_mfspr(SPR_SINGLE_STEP_CONTROL_K);

        if (is_single_step == 0) {
                __insn_mtspr(SPR_SINGLE_STEP_EN_K_K, 0);

        } else if ((*ss_pc != regs->pc) ||
                   (!(control & SPR_SINGLE_STEP_CONTROL_1__CANCELED_MASK))) {

                control |= SPR_SINGLE_STEP_CONTROL_1__CANCELED_MASK;
                control |= SPR_SINGLE_STEP_CONTROL_1__INHIBIT_MASK;
                __insn_mtspr(SPR_SINGLE_STEP_CONTROL_K, control);
                send_sigtrap(current, regs);
        }
}


/*
 * Called from need_singlestep.  Set up the control registers and the enable
 * register, then return back.
 */

void single_step_once(struct pt_regs *regs)
{
        unsigned long *ss_pc = this_cpu_ptr(&ss_saved_pc);
        unsigned long control = __insn_mfspr(SPR_SINGLE_STEP_CONTROL_K);

        *ss_pc = regs->pc;
        control |= SPR_SINGLE_STEP_CONTROL_1__CANCELED_MASK;
        control |= SPR_SINGLE_STEP_CONTROL_1__INHIBIT_MASK;
        __insn_mtspr(SPR_SINGLE_STEP_CONTROL_K, control);
        __insn_mtspr(SPR_SINGLE_STEP_EN_K_K, 1 << USER_PL);
}

void single_step_execve(void)
{
        /* Nothing */
}

#endif /* !__tilegx__ */