Linux 4.1.18

[linux/fpc-iii.git] / arch / x86 / kernel / kgdb.c

/*
 * 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; either version 2, or (at your option) any
 * later version.
 *
 * 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.  See the GNU
 * General Public License for more details.
 *
 */

/*
 * Copyright (C) 2004 Amit S. Kale <amitkale@linsyssoft.com>
 * Copyright (C) 2000-2001 VERITAS Software Corporation.
 * Copyright (C) 2002 Andi Kleen, SuSE Labs
 * Copyright (C) 2004 LinSysSoft Technologies Pvt. Ltd.
 * Copyright (C) 2007 MontaVista Software, Inc.
 * Copyright (C) 2007-2008 Jason Wessel, Wind River Systems, Inc.
 */
/****************************************************************************
 *  Contributor:     Lake Stevens Instrument Division$
 *  Written by:      Glenn Engel $
 *  Updated by:      Amit Kale<akale@veritas.com>
 *  Updated by:      Tom Rini <trini@kernel.crashing.org>
 *  Updated by:      Jason Wessel <jason.wessel@windriver.com>
 *  Modified for 386 by Jim Kingdon, Cygnus Support.
 *  Origianl kgdb, compatibility with 2.1.xx kernel by
 *  David Grothe <dave@gcom.com>
 *  Integrated into 2.2.5 kernel by Tigran Aivazian <tigran@sco.com>
 *  X86_64 changes from Andi Kleen's patch merged by Jim Houston
 */
#include <linux/spinlock.h>
#include <linux/kdebug.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/kgdb.h>
#include <linux/smp.h>
#include <linux/nmi.h>
#include <linux/hw_breakpoint.h>
#include <linux/uaccess.h>
#include <linux/memory.h>

#include <asm/debugreg.h>
#include <asm/apicdef.h>
#include <asm/apic.h>
#include <asm/nmi.h>

struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
{
#ifdef CONFIG_X86_32
        { "ax", 4, offsetof(struct pt_regs, ax) },
        { "cx", 4, offsetof(struct pt_regs, cx) },
        { "dx", 4, offsetof(struct pt_regs, dx) },
        { "bx", 4, offsetof(struct pt_regs, bx) },
        { "sp", 4, offsetof(struct pt_regs, sp) },
        { "bp", 4, offsetof(struct pt_regs, bp) },
        { "si", 4, offsetof(struct pt_regs, si) },
        { "di", 4, offsetof(struct pt_regs, di) },
        { "ip", 4, offsetof(struct pt_regs, ip) },
        { "flags", 4, offsetof(struct pt_regs, flags) },
        { "cs", 4, offsetof(struct pt_regs, cs) },
        { "ss", 4, offsetof(struct pt_regs, ss) },
        { "ds", 4, offsetof(struct pt_regs, ds) },
        { "es", 4, offsetof(struct pt_regs, es) },
#else
        { "ax", 8, offsetof(struct pt_regs, ax) },
        { "bx", 8, offsetof(struct pt_regs, bx) },
        { "cx", 8, offsetof(struct pt_regs, cx) },
        { "dx", 8, offsetof(struct pt_regs, dx) },
        { "si", 8, offsetof(struct pt_regs, si) },
        { "di", 8, offsetof(struct pt_regs, di) },
        { "bp", 8, offsetof(struct pt_regs, bp) },
        { "sp", 8, offsetof(struct pt_regs, sp) },
        { "r8", 8, offsetof(struct pt_regs, r8) },
        { "r9", 8, offsetof(struct pt_regs, r9) },
        { "r10", 8, offsetof(struct pt_regs, r10) },
        { "r11", 8, offsetof(struct pt_regs, r11) },
        { "r12", 8, offsetof(struct pt_regs, r12) },
        { "r13", 8, offsetof(struct pt_regs, r13) },
        { "r14", 8, offsetof(struct pt_regs, r14) },
        { "r15", 8, offsetof(struct pt_regs, r15) },
        { "ip", 8, offsetof(struct pt_regs, ip) },
        { "flags", 4, offsetof(struct pt_regs, flags) },
        { "cs", 4, offsetof(struct pt_regs, cs) },
        { "ss", 4, offsetof(struct pt_regs, ss) },
        { "ds", 4, -1 },
        { "es", 4, -1 },
#endif
        { "fs", 4, -1 },
        { "gs", 4, -1 },
};

int dbg_set_reg(int regno, void *mem, struct pt_regs *regs)
{
        if (
#ifdef CONFIG_X86_32
            regno == GDB_SS || regno == GDB_FS || regno == GDB_GS ||
#endif
            regno == GDB_SP || regno == GDB_ORIG_AX)
                return 0;

        if (dbg_reg_def[regno].offset != -1)
                memcpy((void *)regs + dbg_reg_def[regno].offset, mem,
                       dbg_reg_def[regno].size);
        return 0;
}

char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs)
{
        if (regno == GDB_ORIG_AX) {
                memcpy(mem, &regs->orig_ax, sizeof(regs->orig_ax));
                return "orig_ax";
        }
        if (regno >= DBG_MAX_REG_NUM || regno < 0)
                return NULL;

        if (dbg_reg_def[regno].offset != -1)
                memcpy(mem, (void *)regs + dbg_reg_def[regno].offset,
                       dbg_reg_def[regno].size);

#ifdef CONFIG_X86_32
        switch (regno) {
        case GDB_SS:
                if (!user_mode(regs))
                        *(unsigned long *)mem = __KERNEL_DS;
                break;
        case GDB_SP:
                if (!user_mode(regs))
                        *(unsigned long *)mem = kernel_stack_pointer(regs);
                break;
        case GDB_GS:
        case GDB_FS:
                *(unsigned long *)mem = 0xFFFF;
                break;
        }
#endif
        return dbg_reg_def[regno].name;
}

/**
 *      sleeping_thread_to_gdb_regs - Convert ptrace regs to GDB regs
 *      @gdb_regs: A pointer to hold the registers in the order GDB wants.
 *      @p: The &struct task_struct of the desired process.
 *
 *      Convert the register values of the sleeping process in @p to
 *      the format that GDB expects.
 *      This function is called when kgdb does not have access to the
 *      &struct pt_regs and therefore it should fill the gdb registers
 *      @gdb_regs with what has been saved in &struct thread_struct
 *      thread field during switch_to.
 */
void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
{
#ifndef CONFIG_X86_32
        u32 *gdb_regs32 = (u32 *)gdb_regs;
#endif
        gdb_regs[GDB_AX]        = 0;
        gdb_regs[GDB_BX]        = 0;
        gdb_regs[GDB_CX]        = 0;
        gdb_regs[GDB_DX]        = 0;
        gdb_regs[GDB_SI]        = 0;
        gdb_regs[GDB_DI]        = 0;
        gdb_regs[GDB_BP]        = *(unsigned long *)p->thread.sp;
#ifdef CONFIG_X86_32
        gdb_regs[GDB_DS]        = __KERNEL_DS;
        gdb_regs[GDB_ES]        = __KERNEL_DS;
        gdb_regs[GDB_PS]        = 0;
        gdb_regs[GDB_CS]        = __KERNEL_CS;
        gdb_regs[GDB_PC]        = p->thread.ip;
        gdb_regs[GDB_SS]        = __KERNEL_DS;
        gdb_regs[GDB_FS]        = 0xFFFF;
        gdb_regs[GDB_GS]        = 0xFFFF;
#else
        gdb_regs32[GDB_PS]      = *(unsigned long *)(p->thread.sp + 8);
        gdb_regs32[GDB_CS]      = __KERNEL_CS;
        gdb_regs32[GDB_SS]      = __KERNEL_DS;
        gdb_regs[GDB_PC]        = 0;
        gdb_regs[GDB_R8]        = 0;
        gdb_regs[GDB_R9]        = 0;
        gdb_regs[GDB_R10]       = 0;
        gdb_regs[GDB_R11]       = 0;
        gdb_regs[GDB_R12]       = 0;
        gdb_regs[GDB_R13]       = 0;
        gdb_regs[GDB_R14]       = 0;
        gdb_regs[GDB_R15]       = 0;
#endif
        gdb_regs[GDB_SP]        = p->thread.sp;
}

static struct hw_breakpoint {
        unsigned                enabled;
        unsigned long           addr;
        int                     len;
        int                     type;
        struct perf_event       * __percpu *pev;
} breakinfo[HBP_NUM];

static unsigned long early_dr7;

static void kgdb_correct_hw_break(void)
{
        int breakno;

        for (breakno = 0; breakno < HBP_NUM; breakno++) {
                struct perf_event *bp;
                struct arch_hw_breakpoint *info;
                int val;
                int cpu = raw_smp_processor_id();
                if (!breakinfo[breakno].enabled)
                        continue;
                if (dbg_is_early) {
                        set_debugreg(breakinfo[breakno].addr, breakno);
                        early_dr7 |= encode_dr7(breakno,
                                                breakinfo[breakno].len,
                                                breakinfo[breakno].type);
                        set_debugreg(early_dr7, 7);
                        continue;
                }
                bp = *per_cpu_ptr(breakinfo[breakno].pev, cpu);
                info = counter_arch_bp(bp);
                if (bp->attr.disabled != 1)
                        continue;
                bp->attr.bp_addr = breakinfo[breakno].addr;
                bp->attr.bp_len = breakinfo[breakno].len;
                bp->attr.bp_type = breakinfo[breakno].type;
                info->address = breakinfo[breakno].addr;
                info->len = breakinfo[breakno].len;
                info->type = breakinfo[breakno].type;
                val = arch_install_hw_breakpoint(bp);
                if (!val)
                        bp->attr.disabled = 0;
        }
        if (!dbg_is_early)
                hw_breakpoint_restore();
}

static int hw_break_reserve_slot(int breakno)
{
        int cpu;
        int cnt = 0;
        struct perf_event **pevent;

        if (dbg_is_early)
                return 0;

        for_each_online_cpu(cpu) {
                cnt++;
                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
                if (dbg_reserve_bp_slot(*pevent))
                        goto fail;
        }

        return 0;

fail:
        for_each_online_cpu(cpu) {
                cnt--;
                if (!cnt)
                        break;
                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
                dbg_release_bp_slot(*pevent);
        }
        return -1;
}

static int hw_break_release_slot(int breakno)
{
        struct perf_event **pevent;
        int cpu;

        if (dbg_is_early)
                return 0;

        for_each_online_cpu(cpu) {
                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
                if (dbg_release_bp_slot(*pevent))
                        /*
                         * The debugger is responsible for handing the retry on
                         * remove failure.
                         */
                        return -1;
        }
        return 0;
}

static int
kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
{
        int i;

        for (i = 0; i < HBP_NUM; i++)
                if (breakinfo[i].addr == addr && breakinfo[i].enabled)
                        break;
        if (i == HBP_NUM)
                return -1;

        if (hw_break_release_slot(i)) {
                printk(KERN_ERR "Cannot remove hw breakpoint at %lx\n", addr);
                return -1;
        }
        breakinfo[i].enabled = 0;

        return 0;
}

static void kgdb_remove_all_hw_break(void)
{
        int i;
        int cpu = raw_smp_processor_id();
        struct perf_event *bp;

        for (i = 0; i < HBP_NUM; i++) {
                if (!breakinfo[i].enabled)
                        continue;
                bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
                if (!bp->attr.disabled) {
                        arch_uninstall_hw_breakpoint(bp);
                        bp->attr.disabled = 1;
                        continue;
                }
                if (dbg_is_early)
                        early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
                                                 breakinfo[i].type);
                else if (hw_break_release_slot(i))
                        printk(KERN_ERR "KGDB: hw bpt remove failed %lx\n",
                               breakinfo[i].addr);
                breakinfo[i].enabled = 0;
        }
}

static int
kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
{
        int i;

        for (i = 0; i < HBP_NUM; i++)
                if (!breakinfo[i].enabled)
                        break;
        if (i == HBP_NUM)
                return -1;

        switch (bptype) {
        case BP_HARDWARE_BREAKPOINT:
                len = 1;
                breakinfo[i].type = X86_BREAKPOINT_EXECUTE;
                break;
        case BP_WRITE_WATCHPOINT:
                breakinfo[i].type = X86_BREAKPOINT_WRITE;
                break;
        case BP_ACCESS_WATCHPOINT:
                breakinfo[i].type = X86_BREAKPOINT_RW;
                break;
        default:
                return -1;
        }
        switch (len) {
        case 1:
                breakinfo[i].len = X86_BREAKPOINT_LEN_1;
                break;
        case 2:
                breakinfo[i].len = X86_BREAKPOINT_LEN_2;
                break;
        case 4:
                breakinfo[i].len = X86_BREAKPOINT_LEN_4;
                break;
#ifdef CONFIG_X86_64
        case 8:
                breakinfo[i].len = X86_BREAKPOINT_LEN_8;
                break;
#endif
        default:
                return -1;
        }
        breakinfo[i].addr = addr;
        if (hw_break_reserve_slot(i)) {
                breakinfo[i].addr = 0;
                return -1;
        }
        breakinfo[i].enabled = 1;

        return 0;
}

/**
 *      kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
 *      @regs: Current &struct pt_regs.
 *
 *      This function will be called if the particular architecture must
 *      disable hardware debugging while it is processing gdb packets or
 *      handling exception.
 */
static void kgdb_disable_hw_debug(struct pt_regs *regs)
{
        int i;
        int cpu = raw_smp_processor_id();
        struct perf_event *bp;

        /* Disable hardware debugging while we are in kgdb: */
        set_debugreg(0UL, 7);
        for (i = 0; i < HBP_NUM; i++) {
                if (!breakinfo[i].enabled)
                        continue;
                if (dbg_is_early) {
                        early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
                                                 breakinfo[i].type);
                        continue;
                }
                bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
                if (bp->attr.disabled == 1)
                        continue;
                arch_uninstall_hw_breakpoint(bp);
                bp->attr.disabled = 1;
        }
}

#ifdef CONFIG_SMP
/**
 *      kgdb_roundup_cpus - Get other CPUs into a holding pattern
 *      @flags: Current IRQ state
 *
 *      On SMP systems, we need to get the attention of the other CPUs
 *      and get them be in a known state.  This should do what is needed
 *      to get the other CPUs to call kgdb_wait(). Note that on some arches,
 *      the NMI approach is not used for rounding up all the CPUs. For example,
 *      in case of MIPS, smp_call_function() is used to roundup CPUs. In
 *      this case, we have to make sure that interrupts are enabled before
 *      calling smp_call_function(). The argument to this function is
 *      the flags that will be used when restoring the interrupts. There is
 *      local_irq_save() call before kgdb_roundup_cpus().
 *
 *      On non-SMP systems, this is not called.
 */
void kgdb_roundup_cpus(unsigned long flags)
{
        apic->send_IPI_allbutself(APIC_DM_NMI);
}
#endif

/**
 *      kgdb_arch_handle_exception - Handle architecture specific GDB packets.
 *      @e_vector: The error vector of the exception that happened.
 *      @signo: The signal number of the exception that happened.
 *      @err_code: The error code of the exception that happened.
 *      @remcomInBuffer: The buffer of the packet we have read.
 *      @remcomOutBuffer: The buffer of %BUFMAX bytes to write a packet into.
 *      @linux_regs: The &struct pt_regs of the current process.
 *
 *      This function MUST handle the 'c' and 's' command packets,
 *      as well packets to set / remove a hardware breakpoint, if used.
 *      If there are additional packets which the hardware needs to handle,
 *      they are handled here.  The code should return -1 if it wants to
 *      process more packets, and a %0 or %1 if it wants to exit from the
 *      kgdb callback.
 */
int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
                               char *remcomInBuffer, char *remcomOutBuffer,
                               struct pt_regs *linux_regs)
{
        unsigned long addr;
        char *ptr;

        switch (remcomInBuffer[0]) {
        case 'c':
        case 's':
                /* try to read optional parameter, pc unchanged if no parm */
                ptr = &remcomInBuffer[1];
                if (kgdb_hex2long(&ptr, &addr))
                        linux_regs->ip = addr;
        case 'D':
        case 'k':
                /* clear the trace bit */
                linux_regs->flags &= ~X86_EFLAGS_TF;
                atomic_set(&kgdb_cpu_doing_single_step, -1);

                /* set the trace bit if we're stepping */
                if (remcomInBuffer[0] == 's') {
                        linux_regs->flags |= X86_EFLAGS_TF;
                        atomic_set(&kgdb_cpu_doing_single_step,
                                   raw_smp_processor_id());
                }

                return 0;
        }

        /* this means that we do not want to exit from the handler: */
        return -1;
}

static inline int
single_step_cont(struct pt_regs *regs, struct die_args *args)
{
        /*
         * Single step exception from kernel space to user space so
         * eat the exception and continue the process:
         */
        printk(KERN_ERR "KGDB: trap/step from kernel to user space, "
                        "resuming...\n");
        kgdb_arch_handle_exception(args->trapnr, args->signr,
                                   args->err, "c", "", regs);
        /*
         * Reset the BS bit in dr6 (pointed by args->err) to
         * denote completion of processing
         */
        (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;

        return NOTIFY_STOP;
}

static int was_in_debug_nmi[NR_CPUS];

static int kgdb_nmi_handler(unsigned int cmd, struct pt_regs *regs)
{
        switch (cmd) {
        case NMI_LOCAL:
                if (atomic_read(&kgdb_active) != -1) {
                        /* KGDB CPU roundup */
                        kgdb_nmicallback(raw_smp_processor_id(), regs);
                        was_in_debug_nmi[raw_smp_processor_id()] = 1;
                        touch_nmi_watchdog();
                        return NMI_HANDLED;
                }
                break;

        case NMI_UNKNOWN:
                if (was_in_debug_nmi[raw_smp_processor_id()]) {
                        was_in_debug_nmi[raw_smp_processor_id()] = 0;
                        return NMI_HANDLED;
                }
                break;
        default:
                /* do nothing */
                break;
        }
        return NMI_DONE;
}

static int __kgdb_notify(struct die_args *args, unsigned long cmd)
{
        struct pt_regs *regs = args->regs;

        switch (cmd) {
        case DIE_DEBUG:
                if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
                        if (user_mode(regs))
                                return single_step_cont(regs, args);
                        break;
                } else if (test_thread_flag(TIF_SINGLESTEP))
                        /* This means a user thread is single stepping
                         * a system call which should be ignored
                         */
                        return NOTIFY_DONE;
                /* fall through */
        default:
                if (user_mode(regs))
                        return NOTIFY_DONE;
        }

        if (kgdb_handle_exception(args->trapnr, args->signr, cmd, regs))
                return NOTIFY_DONE;

        /* Must touch watchdog before return to normal operation */
        touch_nmi_watchdog();
        return NOTIFY_STOP;
}

int kgdb_ll_trap(int cmd, const char *str,
                 struct pt_regs *regs, long err, int trap, int sig)
{
        struct die_args args = {
                .regs   = regs,
                .str    = str,
                .err    = err,
                .trapnr = trap,
                .signr  = sig,

        };

        if (!kgdb_io_module_registered)
                return NOTIFY_DONE;

        return __kgdb_notify(&args, cmd);
}

static int
kgdb_notify(struct notifier_block *self, unsigned long cmd, void *ptr)
{
        unsigned long flags;
        int ret;

        local_irq_save(flags);
        ret = __kgdb_notify(ptr, cmd);
        local_irq_restore(flags);

        return ret;
}

static struct notifier_block kgdb_notifier = {
        .notifier_call  = kgdb_notify,
};

/**
 *      kgdb_arch_init - Perform any architecture specific initalization.
 *
 *      This function will handle the initalization of any architecture
 *      specific callbacks.
 */
int kgdb_arch_init(void)
{
        int retval;

        retval = register_die_notifier(&kgdb_notifier);
        if (retval)
                goto out;

        retval = register_nmi_handler(NMI_LOCAL, kgdb_nmi_handler,
                                        0, "kgdb");
        if (retval)
                goto out1;

        retval = register_nmi_handler(NMI_UNKNOWN, kgdb_nmi_handler,
                                        0, "kgdb");

        if (retval)
                goto out2;

        return retval;

out2:
        unregister_nmi_handler(NMI_LOCAL, "kgdb");
out1:
        unregister_die_notifier(&kgdb_notifier);
out:
        return retval;
}

static void kgdb_hw_overflow_handler(struct perf_event *event,
                struct perf_sample_data *data, struct pt_regs *regs)
{
        struct task_struct *tsk = current;
        int i;

        for (i = 0; i < 4; i++)
                if (breakinfo[i].enabled)
                        tsk->thread.debugreg6 |= (DR_TRAP0 << i);
}

void kgdb_arch_late(void)
{
        int i, cpu;
        struct perf_event_attr attr;
        struct perf_event **pevent;

        /*
         * Pre-allocate the hw breakpoint structions in the non-atomic
         * portion of kgdb because this operation requires mutexs to
         * complete.
         */
        hw_breakpoint_init(&attr);
        attr.bp_addr = (unsigned long)kgdb_arch_init;
        attr.bp_len = HW_BREAKPOINT_LEN_1;
        attr.bp_type = HW_BREAKPOINT_W;
        attr.disabled = 1;
        for (i = 0; i < HBP_NUM; i++) {
                if (breakinfo[i].pev)
                        continue;
                breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL, NULL);
                if (IS_ERR((void * __force)breakinfo[i].pev)) {
                        printk(KERN_ERR "kgdb: Could not allocate hw"
                               "breakpoints\nDisabling the kernel debugger\n");
                        breakinfo[i].pev = NULL;
                        kgdb_arch_exit();
                        return;
                }
                for_each_online_cpu(cpu) {
                        pevent = per_cpu_ptr(breakinfo[i].pev, cpu);
                        pevent[0]->hw.sample_period = 1;
                        pevent[0]->overflow_handler = kgdb_hw_overflow_handler;
                        if (pevent[0]->destroy != NULL) {
                                pevent[0]->destroy = NULL;
                                release_bp_slot(*pevent);
                        }
                }
        }
}

/**
 *      kgdb_arch_exit - Perform any architecture specific uninitalization.
 *
 *      This function will handle the uninitalization of any architecture
 *      specific callbacks, for dynamic registration and unregistration.
 */
void kgdb_arch_exit(void)
{
        int i;
        for (i = 0; i < 4; i++) {
                if (breakinfo[i].pev) {
                        unregister_wide_hw_breakpoint(breakinfo[i].pev);
                        breakinfo[i].pev = NULL;
                }
        }
        unregister_nmi_handler(NMI_UNKNOWN, "kgdb");
        unregister_nmi_handler(NMI_LOCAL, "kgdb");
        unregister_die_notifier(&kgdb_notifier);
}

/**
 *
 *      kgdb_skipexception - Bail out of KGDB when we've been triggered.
 *      @exception: Exception vector number
 *      @regs: Current &struct pt_regs.
 *
 *      On some architectures we need to skip a breakpoint exception when
 *      it occurs after a breakpoint has been removed.
 *
 * Skip an int3 exception when it occurs after a breakpoint has been
 * removed. Backtrack eip by 1 since the int3 would have caused it to
 * increment by 1.
 */
int kgdb_skipexception(int exception, struct pt_regs *regs)
{
        if (exception == 3 && kgdb_isremovedbreak(regs->ip - 1)) {
                regs->ip -= 1;
                return 1;
        }
        return 0;
}

unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs)
{
        if (exception == 3)
                return instruction_pointer(regs) - 1;
        return instruction_pointer(regs);
}

void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
{
        regs->ip = ip;
}

int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
{
        int err;
#ifdef CONFIG_DEBUG_RODATA
        char opc[BREAK_INSTR_SIZE];
#endif /* CONFIG_DEBUG_RODATA */

        bpt->type = BP_BREAKPOINT;
        err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
                                BREAK_INSTR_SIZE);
        if (err)
                return err;
        err = probe_kernel_write((char *)bpt->bpt_addr,
                                 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
#ifdef CONFIG_DEBUG_RODATA
        if (!err)
                return err;
        /*
         * It is safe to call text_poke() because normal kernel execution
         * is stopped on all cores, so long as the text_mutex is not locked.
         */
        if (mutex_is_locked(&text_mutex))
                return -EBUSY;
        text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
                  BREAK_INSTR_SIZE);
        err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
        if (err)
                return err;
        if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE))
                return -EINVAL;
        bpt->type = BP_POKE_BREAKPOINT;
#endif /* CONFIG_DEBUG_RODATA */
        return err;
}

int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
{
#ifdef CONFIG_DEBUG_RODATA
        int err;
        char opc[BREAK_INSTR_SIZE];

        if (bpt->type != BP_POKE_BREAKPOINT)
                goto knl_write;
        /*
         * It is safe to call text_poke() because normal kernel execution
         * is stopped on all cores, so long as the text_mutex is not locked.
         */
        if (mutex_is_locked(&text_mutex))
                goto knl_write;
        text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE);
        err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
        if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))
                goto knl_write;
        return err;
knl_write:
#endif /* CONFIG_DEBUG_RODATA */
        return probe_kernel_write((char *)bpt->bpt_addr,
                                  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
}

struct kgdb_arch arch_kgdb_ops = {
        /* Breakpoint instruction: */
        .gdb_bpt_instr          = { 0xcc },
        .flags                  = KGDB_HW_BREAKPOINT,
        .set_hw_breakpoint      = kgdb_set_hw_break,
        .remove_hw_breakpoint   = kgdb_remove_hw_break,
        .disable_hw_break       = kgdb_disable_hw_debug,
        .remove_all_hw_break    = kgdb_remove_all_hw_break,
        .correct_hw_break       = kgdb_correct_hw_break,
};