/*
 *  linux/arch/arm/kernel/traps.c
 *
 *  Copyright (C) 1995-2009 Russell King
 *  Fragments that appear the same as linux/arch/i386/kernel/traps.c (C) Linus Torvalds
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 *  'traps.c' handles hardware exceptions after we have saved some state in
 *  'linux/arch/arm/lib/traps.S'.  Mostly a debugging aid, but will probably
 *  kill the offending process.
 */
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/kallsyms.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include <linux/kdebug.h>
#include <linux/module.h>
#include <linux/kexec.h>
#include <linux/bug.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/sched.h>

#include <linux/atomic.h>
#include <asm/cacheflush.h>
#include <asm/exception.h>
#include <asm/unistd.h>
#include <asm/traps.h>
#include <asm/unwind.h>
#include <asm/tls.h>
#include <asm/system_misc.h>

static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };

void *vectors_page;

#ifdef CONFIG_DEBUG_USER
unsigned int user_debug;

static int __init user_debug_setup(char *str)
{
        get_option(&str, &user_debug);
        return 1;
}
__setup("user_debug=", user_debug_setup);
#endif

static void dump_mem(const char *, const char *, unsigned long, unsigned long);

void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame)
{
#ifdef CONFIG_KALLSYMS
        printk("[<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
#else
        printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
#endif

        if (in_exception_text(where))
                dump_mem("", "Exception stack", frame + 4, frame + 4 + sizeof(struct pt_regs));
}

#ifndef CONFIG_ARM_UNWIND
/*
 * Stack pointers should always be within the kernels view of
 * physical memory.  If it is not there, then we can't dump
 * out any information relating to the stack.
 */
static int verify_stack(unsigned long sp)
{
        if (sp < PAGE_OFFSET ||
            (sp > (unsigned long)high_memory && high_memory != NULL))
                return -EFAULT;

        return 0;
}
#endif

/*
 * Dump out the contents of some memory nicely...
 */
static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
                     unsigned long top)
{
        unsigned long first;
        mm_segment_t fs;
        int i;

        /*
         * We need to switch to kernel mode so that we can use __get_user
         * to safely read from kernel space.  Note that we now dump the
         * code first, just in case the backtrace kills us.
         */
        fs = get_fs();
        set_fs(KERNEL_DS);

        printk("%s%s(0x%08lx to 0x%08lx)\n", lvl, str, bottom, top);

        for (first = bottom & ~31; first < top; first += 32) {
                unsigned long p;
                char str[sizeof(" 12345678") * 8 + 1];

                memset(str, ' ', sizeof(str));
                str[sizeof(str) - 1] = '\0';

                for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
                        if (p >= bottom && p < top) {
                                unsigned long val;
                                if (__get_user(val, (unsigned long *)p) == 0)
                                        sprintf(str + i * 9, " %08lx", val);
                                else
                                        sprintf(str + i * 9, " ????????");
                        }
                }
                printk("%s%04lx:%s\n", lvl, first & 0xffff, str);
        }

        set_fs(fs);
}

static void dump_instr(const char *lvl, struct pt_regs *regs)
{
        unsigned long addr = instruction_pointer(regs);
        const int thumb = thumb_mode(regs);
        const int width = thumb ? 4 : 8;
        mm_segment_t fs;
        char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
        int i;

        /*
         * We need to switch to kernel mode so that we can use __get_user
         * to safely read from kernel space.  Note that we now dump the
         * code first, just in case the backtrace kills us.
         */
        fs = get_fs();
        set_fs(KERNEL_DS);

        for (i = -4; i < 1 + !!thumb; i++) {
                unsigned int val, bad;

                if (thumb)
                        bad = __get_user(val, &((u16 *)addr)[i]);
                else
                        bad = __get_user(val, &((u32 *)addr)[i]);

                if (!bad)
                        p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ",
                                        width, val);
                else {
                        p += sprintf(p, "bad PC value");
                        break;
                }
        }
        printk("%sCode: %s\n", lvl, str);

        set_fs(fs);
}

#ifdef CONFIG_ARM_UNWIND
static inline void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
        unwind_backtrace(regs, tsk);
}
#else
static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
        unsigned int fp, mode;
        int ok = 1;

        printk("Backtrace: ");

        if (!tsk)
                tsk = current;

        if (regs) {
                fp = regs->ARM_fp;
                mode = processor_mode(regs);
        } else if (tsk != current) {
                fp = thread_saved_fp(tsk);
                mode = 0x10;
        } else {
                asm("mov %0, fp" : "=r" (fp) : : "cc");
                mode = 0x10;
        }

        if (!fp) {
                printk("no frame pointer");
                ok = 0;
        } else if (verify_stack(fp)) {
                printk("invalid frame pointer 0x%08x", fp);
                ok = 0;
        } else if (fp < (unsigned long)end_of_stack(tsk))
                printk("frame pointer underflow");
        printk("\n");

        if (ok)
                c_backtrace(fp, mode);
}
#endif

void show_stack(struct task_struct *tsk, unsigned long *sp)
{
        dump_backtrace(NULL, tsk);
        barrier();
}

#ifdef CONFIG_PREEMPT
#define S_PREEMPT " PREEMPT"
#else
#define S_PREEMPT ""
#endif
#ifdef CONFIG_SMP
#define S_SMP " SMP"
#else
#define S_SMP ""
#endif
#ifdef CONFIG_THUMB2_KERNEL
#define S_ISA " THUMB2"
#else
#define S_ISA " ARM"
#endif

static int __die(const char *str, int err, struct pt_regs *regs)
{
        struct task_struct *tsk = current;
        static int die_counter;
        int ret;

        printk(KERN_EMERG "Internal error: %s: %x [#%d]" S_PREEMPT S_SMP
               S_ISA "\n", str, err, ++die_counter);

        /* trap and error numbers are mostly meaningless on ARM */
        ret = notify_die(DIE_OOPS, str, regs, err, tsk->thread.trap_no, SIGSEGV);
        if (ret == NOTIFY_STOP)
                return 1;

        print_modules();
        __show_regs(regs);
        printk(KERN_EMERG "Process %.*s (pid: %d, stack limit = 0x%p)\n",
                TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk), end_of_stack(tsk));

        if (!user_mode(regs) || in_interrupt()) {
                dump_mem(KERN_EMERG, "Stack: ", regs->ARM_sp,
                         THREAD_SIZE + (unsigned long)task_stack_page(tsk));
                dump_backtrace(regs, tsk);
                dump_instr(KERN_EMERG, regs);
        }

        return 0;
}

static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED;
static int die_owner = -1;
static unsigned int die_nest_count;

static unsigned long oops_begin(void)
{
        int cpu;
        unsigned long flags;

        oops_enter();

        /* racy, but better than risking deadlock. */
        raw_local_irq_save(flags);
        cpu = smp_processor_id();
        if (!arch_spin_trylock(&die_lock)) {
                if (cpu == die_owner)
                        /* nested oops. should stop eventually */;
                else
                        arch_spin_lock(&die_lock);
        }
        die_nest_count++;
        die_owner = cpu;
        console_verbose();
        bust_spinlocks(1);
        return flags;
}

static void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
{
        if (regs && kexec_should_crash(current))
                crash_kexec(regs);

        bust_spinlocks(0);
        die_owner = -1;
        add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
        die_nest_count--;
        if (!die_nest_count)
                /* Nest count reaches zero, release the lock. */
                arch_spin_unlock(&die_lock);
        raw_local_irq_restore(flags);
        oops_exit();

        if (in_interrupt())
                panic("Fatal exception in interrupt");
        if (panic_on_oops)
                panic("Fatal exception");
        if (signr)
                do_exit(signr);
}

/*
 * This function is protected against re-entrancy.
 */
void die(const char *str, struct pt_regs *regs, int err)
{
        enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;
        unsigned long flags = oops_begin();
        int sig = SIGSEGV;

        if (!user_mode(regs))
                bug_type = report_bug(regs->ARM_pc, regs);
        if (bug_type != BUG_TRAP_TYPE_NONE)
                str = "Oops - BUG";

        if (__die(str, err, regs))
                sig = 0;

        oops_end(flags, regs, sig);
}

void arm_notify_die(const char *str, struct pt_regs *regs,
                struct siginfo *info, unsigned long err, unsigned long trap)
{
        if (user_mode(regs)) {
                current->thread.error_code = err;
                current->thread.trap_no = trap;

                force_sig_info(info->si_signo, info, current);
        } else {
                die(str, regs, err);
        }
}

#ifdef CONFIG_GENERIC_BUG

int is_valid_bugaddr(unsigned long pc)
{
#ifdef CONFIG_THUMB2_KERNEL
        unsigned short bkpt;
#else
        unsigned long bkpt;
#endif

        if (probe_kernel_address((unsigned *)pc, bkpt))
                return 0;

        return bkpt == BUG_INSTR_VALUE;
}

#endif

static LIST_HEAD(undef_hook);
static DEFINE_RAW_SPINLOCK(undef_lock);

void register_undef_hook(struct undef_hook *hook)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&undef_lock, flags);
        list_add(&hook->node, &undef_hook);
        raw_spin_unlock_irqrestore(&undef_lock, flags);
}

void unregister_undef_hook(struct undef_hook *hook)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&undef_lock, flags);
        list_del(&hook->node);
        raw_spin_unlock_irqrestore(&undef_lock, flags);
}

static int call_undef_hook(struct pt_regs *regs, unsigned int instr)
{
        struct undef_hook *hook;
        unsigned long flags;
        int (*fn)(struct pt_regs *regs, unsigned int instr) = NULL;

        raw_spin_lock_irqsave(&undef_lock, flags);
        list_for_each_entry(hook, &undef_hook, node)
                if ((instr & hook->instr_mask) == hook->instr_val &&
                    (regs->ARM_cpsr & hook->cpsr_mask) == hook->cpsr_val)
                        fn = hook->fn;
        raw_spin_unlock_irqrestore(&undef_lock, flags);

        return fn ? fn(regs, instr) : 1;
}

asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
{
        unsigned int instr;
        siginfo_t info;
        void __user *pc;

        pc = (void __user *)instruction_pointer(regs);

        if (processor_mode(regs) == SVC_MODE) {
#ifdef CONFIG_THUMB2_KERNEL
                if (thumb_mode(regs)) {
                        instr = ((u16 *)pc)[0];
                        if (is_wide_instruction(instr)) {
                                instr <<= 16;
                                instr |= ((u16 *)pc)[1];
                        }
                } else
#endif
                        instr = *(u32 *) pc;
        } else if (thumb_mode(regs)) {
                if (get_user(instr, (u16 __user *)pc))
                        goto die_sig;
                if (is_wide_instruction(instr)) {
                        unsigned int instr2;
                        if (get_user(instr2, (u16 __user *)pc+1))
                                goto die_sig;
                        instr <<= 16;
                        instr |= instr2;
                }
        } else if (get_user(instr, (u32 __user *)pc)) {
                goto die_sig;
        }

        if (call_undef_hook(regs, instr) == 0)
                return;

die_sig:
#ifdef CONFIG_DEBUG_USER
        if (user_debug & UDBG_UNDEFINED) {
                printk(KERN_INFO "%s (%d): undefined instruction: pc=%p\n",
                        current->comm, task_pid_nr(current), pc);
                dump_instr(KERN_INFO, regs);
        }
#endif

        info.si_signo = SIGILL;
        info.si_errno = 0;
        info.si_code  = ILL_ILLOPC;
        info.si_addr  = pc;

        arm_notify_die("Oops - undefined instruction", regs, &info, 0, 6);
}

asmlinkage void do_unexp_fiq (struct pt_regs *regs)
{
        printk("Hmm.  Unexpected FIQ received, but trying to continue\n");
        printk("You may have a hardware problem...\n");
}

/*
 * bad_mode handles the impossible case in the vectors.  If you see one of
 * these, then it's extremely serious, and could mean you have buggy hardware.
 * It never returns, and never tries to sync.  We hope that we can at least
 * dump out some state information...
 */
asmlinkage void bad_mode(struct pt_regs *regs, int reason)
{
        console_verbose();

        printk(KERN_CRIT "Bad mode in %s handler detected\n", handler[reason]);

        die("Oops - bad mode", regs, 0);
        local_irq_disable();
        panic("bad mode");
}

static int bad_syscall(int n, struct pt_regs *regs)
{
        struct thread_info *thread = current_thread_info();
        siginfo_t info;

        if ((current->personality & PER_MASK) != PER_LINUX &&
            thread->exec_domain->handler) {
                thread->exec_domain->handler(n, regs);
                return regs->ARM_r0;
        }

#ifdef CONFIG_DEBUG_USER
        if (user_debug & UDBG_SYSCALL) {
                printk(KERN_ERR "[%d] %s: obsolete system call %08x.\n",
                        task_pid_nr(current), current->comm, n);
                dump_instr(KERN_ERR, regs);
        }
#endif

        info.si_signo = SIGILL;
        info.si_errno = 0;
        info.si_code  = ILL_ILLTRP;
        info.si_addr  = (void __user *)instruction_pointer(regs) -
                         (thumb_mode(regs) ? 2 : 4);

        arm_notify_die("Oops - bad syscall", regs, &info, n, 0);

        return regs->ARM_r0;
}

static inline int
do_cache_op(unsigned long start, unsigned long end, int flags)
{
        struct mm_struct *mm = current->active_mm;
        struct vm_area_struct *vma;

        if (end < start || flags)
                return -EINVAL;

        down_read(&mm->mmap_sem);
        vma = find_vma(mm, start);
        if (vma && vma->vm_start < end) {
                if (start < vma->vm_start)
                        start = vma->vm_start;
                if (end > vma->vm_end)
                        end = vma->vm_end;

                up_read(&mm->mmap_sem);
                return flush_cache_user_range(start, end);
        }
        up_read(&mm->mmap_sem);
        return -EINVAL;
}

/*
 * Handle all unrecognised system calls.
 *  0x9f0000 - 0x9fffff are some more esoteric system calls
 */
#define NR(x) ((__ARM_NR_##x) - __ARM_NR_BASE)
asmlinkage int arm_syscall(int no, struct pt_regs *regs)
{
        struct thread_info *thread = current_thread_info();
        siginfo_t info;

        if ((no >> 16) != (__ARM_NR_BASE>> 16))
                return bad_syscall(no, regs);

        switch (no & 0xffff) {
        case 0: /* branch through 0 */
                info.si_signo = SIGSEGV;
                info.si_errno = 0;
                info.si_code  = SEGV_MAPERR;
                info.si_addr  = NULL;

                arm_notify_die("branch through zero", regs, &info, 0, 0);
                return 0;

        case NR(breakpoint): /* SWI BREAK_POINT */
                regs->ARM_pc -= thumb_mode(regs) ? 2 : 4;
                ptrace_break(current, regs);
                return regs->ARM_r0;

        /*
         * Flush a region from virtual address 'r0' to virtual address 'r1'
         * _exclusive_.  There is no alignment requirement on either address;
         * user space does not need to know the hardware cache layout.
         *
         * r2 contains flags.  It should ALWAYS be passed as ZERO until it
         * is defined to be something else.  For now we ignore it, but may
         * the fires of hell burn in your belly if you break this rule. ;)
         *
         * (at a later date, we may want to allow this call to not flush
         * various aspects of the cache.  Passing '0' will guarantee that
         * everything necessary gets flushed to maintain consistency in
         * the specified region).
         */
        case NR(cacheflush):
                return do_cache_op(regs->ARM_r0, regs->ARM_r1, regs->ARM_r2);

        case NR(usr26):
                if (!(elf_hwcap & HWCAP_26BIT))
                        break;
                regs->ARM_cpsr &= ~MODE32_BIT;
                return regs->ARM_r0;

        case NR(usr32):
                if (!(elf_hwcap & HWCAP_26BIT))
                        break;
                regs->ARM_cpsr |= MODE32_BIT;
                return regs->ARM_r0;

        case NR(set_tls):
                thread->tp_value[0] = regs->ARM_r0;
                if (tls_emu)
                        return 0;
                if (has_tls_reg) {
                        asm ("mcr p15, 0, %0, c13, c0, 3"
                                : : "r" (regs->ARM_r0));
                } else {
                        /*
                         * User space must never try to access this directly.
                         * Expect your app to break eventually if you do so.
                         * The user helper at 0xffff0fe0 must be used instead.
                         * (see entry-armv.S for details)
                         */
                        *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
                }
                return 0;

#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
        /*
         * Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
         * Return zero in r0 if *MEM was changed or non-zero if no exchange
         * happened.  Also set the user C flag accordingly.
         * If access permissions have to be fixed up then non-zero is
         * returned and the operation has to be re-attempted.
         *
         * *NOTE*: This is a ghost syscall private to the kernel.  Only the
         * __kuser_cmpxchg code in entry-armv.S should be aware of its
         * existence.  Don't ever use this from user code.
         */
        case NR(cmpxchg):
        for (;;) {
                extern void do_DataAbort(unsigned long addr, unsigned int fsr,
                                         struct pt_regs *regs);
                unsigned long val;
                unsigned long addr = regs->ARM_r2;
                struct mm_struct *mm = current->mm;
                pgd_t *pgd; pmd_t *pmd; pte_t *pte;
                spinlock_t *ptl;

                regs->ARM_cpsr &= ~PSR_C_BIT;
                down_read(&mm->mmap_sem);
                pgd = pgd_offset(mm, addr);
                if (!pgd_present(*pgd))
                        goto bad_access;
                pmd = pmd_offset(pgd, addr);
                if (!pmd_present(*pmd))
                        goto bad_access;
                pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
                if (!pte_present(*pte) || !pte_write(*pte) || !pte_dirty(*pte)) {
                        pte_unmap_unlock(pte, ptl);
                        goto bad_access;
                }
                val = *(unsigned long *)addr;
                val -= regs->ARM_r0;
                if (val == 0) {
                        *(unsigned long *)addr = regs->ARM_r1;
                        regs->ARM_cpsr |= PSR_C_BIT;
                }
                pte_unmap_unlock(pte, ptl);
                up_read(&mm->mmap_sem);
                return val;

                bad_access:
                up_read(&mm->mmap_sem);
                /* simulate a write access fault */
                do_DataAbort(addr, 15 + (1 << 11), regs);
        }
#endif

        default:
                /* Calls 9f00xx..9f07ff are defined to return -ENOSYS
                   if not implemented, rather than raising SIGILL.  This
                   way the calling program can gracefully determine whether
                   a feature is supported.  */
                if ((no & 0xffff) <= 0x7ff)
                        return -ENOSYS;
                break;
        }
#ifdef CONFIG_DEBUG_USER
        /*
         * experience shows that these seem to indicate that
         * something catastrophic has happened
         */
        if (user_debug & UDBG_SYSCALL) {
                printk("[%d] %s: arm syscall %d\n",
                       task_pid_nr(current), current->comm, no);
                dump_instr("", regs);
                if (user_mode(regs)) {
                        __show_regs(regs);
                        c_backtrace(regs->ARM_fp, processor_mode(regs));
                }
        }
#endif
        info.si_signo = SIGILL;
        info.si_errno = 0;
        info.si_code  = ILL_ILLTRP;
        info.si_addr  = (void __user *)instruction_pointer(regs) -
                         (thumb_mode(regs) ? 2 : 4);

        arm_notify_die("Oops - bad syscall(2)", regs, &info, no, 0);
        return 0;
}

#ifdef CONFIG_TLS_REG_EMUL

/*
 * We might be running on an ARMv6+ processor which should have the TLS
 * register but for some reason we can't use it, or maybe an SMP system
 * using a pre-ARMv6 processor (there are apparently a few prototypes like
 * that in existence) and therefore access to that register must be
 * emulated.
 */

static int get_tp_trap(struct pt_regs *regs, unsigned int instr)
{
        int reg = (instr >> 12) & 15;
        if (reg == 15)
                return 1;
        regs->uregs[reg] = current_thread_info()->tp_value[0];
        regs->ARM_pc += 4;
        return 0;
}

static struct undef_hook arm_mrc_hook = {
        .instr_mask     = 0x0fff0fff,
        .instr_val      = 0x0e1d0f70,
        .cpsr_mask      = PSR_T_BIT,
        .cpsr_val       = 0,
        .fn             = get_tp_trap,
};

static int __init arm_mrc_hook_init(void)
{
        register_undef_hook(&arm_mrc_hook);
        return 0;
}

late_initcall(arm_mrc_hook_init);

#endif

void __bad_xchg(volatile void *ptr, int size)
{
        printk("xchg: bad data size: pc 0x%p, ptr 0x%p, size %d\n",
                __builtin_return_address(0), ptr, size);
        BUG();
}
EXPORT_SYMBOL(__bad_xchg);

/*
 * A data abort trap was taken, but we did not handle the instruction.
 * Try to abort the user program, or panic if it was the kernel.
 */
asmlinkage void
baddataabort(int code, unsigned long instr, struct pt_regs *regs)
{
        unsigned long addr = instruction_pointer(regs);
        siginfo_t info;

#ifdef CONFIG_DEBUG_USER
        if (user_debug & UDBG_BADABORT) {
                printk(KERN_ERR "[%d] %s: bad data abort: code %d instr 0x%08lx\n",
                        task_pid_nr(current), current->comm, code, instr);
                dump_instr(KERN_ERR, regs);
                show_pte(current->mm, addr);
        }
#endif

        info.si_signo = SIGILL;
        info.si_errno = 0;
        info.si_code  = ILL_ILLOPC;
        info.si_addr  = (void __user *)addr;

        arm_notify_die("unknown data abort code", regs, &info, instr, 0);
}

void __readwrite_bug(const char *fn)
{
        printk("%s called, but not implemented\n", fn);
        BUG();
}
EXPORT_SYMBOL(__readwrite_bug);

void __pte_error(const char *file, int line, pte_t pte)
{
        printk("%s:%d: bad pte %08llx.\n", file, line, (long long)pte_val(pte));
}

void __pmd_error(const char *file, int line, pmd_t pmd)
{
        printk("%s:%d: bad pmd %08llx.\n", file, line, (long long)pmd_val(pmd));
}

void __pgd_error(const char *file, int line, pgd_t pgd)
{
        printk("%s:%d: bad pgd %08llx.\n", file, line, (long long)pgd_val(pgd));
}

asmlinkage void __div0(void)
{
        printk("Division by zero in kernel.\n");
        dump_stack();
}
EXPORT_SYMBOL(__div0);

void abort(void)
{
        BUG();

        /* if that doesn't kill us, halt */
        panic("Oops failed to kill thread");
}
EXPORT_SYMBOL(abort);

void __init trap_init(void)
{
        return;
}

#ifdef CONFIG_KUSER_HELPERS
static void __init kuser_init(void *vectors)
{
        extern char __kuser_helper_start[], __kuser_helper_end[];
        int kuser_sz = __kuser_helper_end - __kuser_helper_start;

        memcpy(vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);

        /*
         * vectors + 0xfe0 = __kuser_get_tls
         * vectors + 0xfe8 = hardware TLS instruction at 0xffff0fe8
         */
        if (tls_emu || has_tls_reg)
                memcpy(vectors + 0xfe0, vectors + 0xfe8, 4);
}
#else
static void __init kuser_init(void *vectors)
{
}
#endif

void __init early_trap_init(void *vectors_base)
{
#ifndef CONFIG_CPU_V7M
        unsigned long vectors = (unsigned long)vectors_base;
        extern char __stubs_start[], __stubs_end[];
        extern char __vectors_start[], __vectors_end[];
        unsigned i;

        vectors_page = vectors_base;

        /*
         * Poison the vectors page with an undefined instruction.  This
         * instruction is chosen to be undefined for both ARM and Thumb
         * ISAs.  The Thumb version is an undefined instruction with a
         * branch back to the undefined instruction.
         */
        for (i = 0; i < PAGE_SIZE / sizeof(u32); i++)
                ((u32 *)vectors_base)[i] = 0xe7fddef1;

        /*
         * Copy the vectors, stubs and kuser helpers (in entry-armv.S)
         * into the vector page, mapped at 0xffff0000, and ensure these
         * are visible to the instruction stream.
         */
        memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);
        memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);

        kuser_init(vectors_base);

        flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
        modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
#else /* ifndef CONFIG_CPU_V7M */
        /*
         * on V7-M there is no need to copy the vector table to a dedicated
         * memory area. The address is configurable and so a table in the kernel
         * image can be used.
         */
#endif
}