#include <linux/extable.h>
#include <linux/uaccess.h>
#include <linux/sched/debug.h>

#include <asm/traps.h>
#include <asm/kdebug.h>

typedef bool (*ex_handler_t)(const struct exception_table_entry *,
                            struct pt_regs *, int);

static inline unsigned long
ex_fixup_addr(const struct exception_table_entry *x)
{
        return (unsigned long)&x->fixup + x->fixup;
}
static inline ex_handler_t
ex_fixup_handler(const struct exception_table_entry *x)
{
        return (ex_handler_t)((unsigned long)&x->handler + x->handler);
}

bool ex_handler_default(const struct exception_table_entry *fixup,
                       struct pt_regs *regs, int trapnr)
{
        regs->ip = ex_fixup_addr(fixup);
        return true;
}
EXPORT_SYMBOL(ex_handler_default);

bool ex_handler_fault(const struct exception_table_entry *fixup,
                     struct pt_regs *regs, int trapnr)
{
        regs->ip = ex_fixup_addr(fixup);
        regs->ax = trapnr;
        return true;
}
EXPORT_SYMBOL_GPL(ex_handler_fault);

bool ex_handler_ext(const struct exception_table_entry *fixup,
                   struct pt_regs *regs, int trapnr)
{
        /* Special hack for uaccess_err */
        current->thread.uaccess_err = 1;
        regs->ip = ex_fixup_addr(fixup);
        return true;
}
EXPORT_SYMBOL(ex_handler_ext);

bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
                             struct pt_regs *regs, int trapnr)
{
        if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n",
                         (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
                show_stack_regs(regs);

        /* Pretend that the read succeeded and returned 0. */
        regs->ip = ex_fixup_addr(fixup);
        regs->ax = 0;
        regs->dx = 0;
        return true;
}
EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);

bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
                             struct pt_regs *regs, int trapnr)
{
        if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n",
                         (unsigned int)regs->cx, (unsigned int)regs->dx,
                         (unsigned int)regs->ax,  regs->ip, (void *)regs->ip))
                show_stack_regs(regs);

        /* Pretend that the write succeeded. */
        regs->ip = ex_fixup_addr(fixup);
        return true;
}
EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);

bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
                         struct pt_regs *regs, int trapnr)
{
        if (static_cpu_has(X86_BUG_NULL_SEG))
                asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
        asm volatile ("mov %0, %%fs" : : "rm" (0));
        return ex_handler_default(fixup, regs, trapnr);
}
EXPORT_SYMBOL(ex_handler_clear_fs);

bool ex_has_fault_handler(unsigned long ip)
{
        const struct exception_table_entry *e;
        ex_handler_t handler;

        e = search_exception_tables(ip);
        if (!e)
                return false;
        handler = ex_fixup_handler(e);

        return handler == ex_handler_fault;
}

int fixup_exception(struct pt_regs *regs, int trapnr)
{
        const struct exception_table_entry *e;
        ex_handler_t handler;

#ifdef CONFIG_PNPBIOS
        if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
                extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
                extern u32 pnp_bios_is_utter_crap;
                pnp_bios_is_utter_crap = 1;
                printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
                __asm__ volatile(
                        "movl %0, %%esp\n\t"
                        "jmp *%1\n\t"
                        : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
                panic("do_trap: can't hit this");
        }
#endif

        e = search_exception_tables(regs->ip);
        if (!e)
                return 0;

        handler = ex_fixup_handler(e);
        return handler(e, regs, trapnr);
}

extern unsigned int early_recursion_flag;

/* Restricted version used during very early boot */
void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
{
        /* Ignore early NMIs. */
        if (trapnr == X86_TRAP_NMI)
                return;

        if (early_recursion_flag > 2)
                goto halt_loop;

        /*
         * Old CPUs leave the high bits of CS on the stack
         * undefined.  I'm not sure which CPUs do this, but at least
         * the 486 DX works this way.
         */
        if ((regs->cs & 0xFFFF) != __KERNEL_CS)
                goto fail;

        /*
         * The full exception fixup machinery is available as soon as
         * the early IDT is loaded.  This means that it is the
         * responsibility of extable users to either function correctly
         * when handlers are invoked early or to simply avoid causing
         * exceptions before they're ready to handle them.
         *
         * This is better than filtering which handlers can be used,
         * because refusing to call a handler here is guaranteed to
         * result in a hard-to-debug panic.
         *
         * Keep in mind that not all vectors actually get here.  Early
         * fage faults, for example, are special.
         */
        if (fixup_exception(regs, trapnr))
                return;

        if (fixup_bug(regs, trapnr))
                return;

fail:
        early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
                     (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
                     regs->orig_ax, read_cr2());

        show_regs(regs);

halt_loop:
        while (true)
                halt();
}