[PATCH] x86: privilege cleanup

[deliverable/linux.git] / arch / i386 / kernel / traps.c

/*
 *  linux/arch/i386/traps.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */

/*
 * 'Traps.c' handles hardware traps and faults after we have saved some
 * state in 'asm.s'.
 */
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/highmem.h>
#include <linux/kallsyms.h>
#include <linux/ptrace.h>
#include <linux/utsname.h>
#include <linux/kprobes.h>
#include <linux/kexec.h>

#ifdef CONFIG_EISA
#include <linux/ioport.h>
#include <linux/eisa.h>
#endif

#ifdef CONFIG_MCA
#include <linux/mca.h>
#endif

#include <asm/processor.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/atomic.h>
#include <asm/debugreg.h>
#include <asm/desc.h>
#include <asm/i387.h>
#include <asm/nmi.h>

#include <asm/smp.h>
#include <asm/arch_hooks.h>
#include <asm/kdebug.h>

#include <linux/irq.h>
#include <linux/module.h>

#include "mach_traps.h"

asmlinkage int system_call(void);

struct desc_struct default_ldt[] = { { 0, 0 }, { 0, 0 }, { 0, 0 },
                { 0, 0 }, { 0, 0 } };

/* Do we ignore FPU interrupts ? */
char ignore_fpu_irq = 0;

/*
 * The IDT has to be page-aligned to simplify the Pentium
 * F0 0F bug workaround.. We have a special link segment
 * for this.
 */
struct desc_struct idt_table[256] __attribute__((__section__(".data.idt"))) = { {0, 0}, };

asmlinkage void divide_error(void);
asmlinkage void debug(void);
asmlinkage void nmi(void);
asmlinkage void int3(void);
asmlinkage void overflow(void);
asmlinkage void bounds(void);
asmlinkage void invalid_op(void);
asmlinkage void device_not_available(void);
asmlinkage void coprocessor_segment_overrun(void);
asmlinkage void invalid_TSS(void);
asmlinkage void segment_not_present(void);
asmlinkage void stack_segment(void);
asmlinkage void general_protection(void);
asmlinkage void page_fault(void);
asmlinkage void coprocessor_error(void);
asmlinkage void simd_coprocessor_error(void);
asmlinkage void alignment_check(void);
asmlinkage void spurious_interrupt_bug(void);
asmlinkage void machine_check(void);

static int kstack_depth_to_print = 24;
struct notifier_block *i386die_chain;
static DEFINE_SPINLOCK(die_notifier_lock);

int register_die_notifier(struct notifier_block *nb)
{
        int err = 0;
        unsigned long flags;
        spin_lock_irqsave(&die_notifier_lock, flags);
        err = notifier_chain_register(&i386die_chain, nb);
        spin_unlock_irqrestore(&die_notifier_lock, flags);
        return err;
}
EXPORT_SYMBOL(register_die_notifier);

static inline int valid_stack_ptr(struct thread_info *tinfo, void *p)
{
        return  p > (void *)tinfo &&
                p < (void *)tinfo + THREAD_SIZE - 3;
}

static inline unsigned long print_context_stack(struct thread_info *tinfo,
                                unsigned long *stack, unsigned long ebp)
{
        unsigned long addr;

#ifdef  CONFIG_FRAME_POINTER
        while (valid_stack_ptr(tinfo, (void *)ebp)) {
                addr = *(unsigned long *)(ebp + 4);
                printk(" [<%08lx>] ", addr);
                print_symbol("%s", addr);
                printk("\n");
                ebp = *(unsigned long *)ebp;
        }
#else
        while (valid_stack_ptr(tinfo, stack)) {
                addr = *stack++;
                if (__kernel_text_address(addr)) {
                        printk(" [<%08lx>]", addr);
                        print_symbol(" %s", addr);
                        printk("\n");
                }
        }
#endif
        return ebp;
}

void show_trace(struct task_struct *task, unsigned long * stack)
{
        unsigned long ebp;

        if (!task)
                task = current;

        if (task == current) {
                /* Grab ebp right from our regs */
                asm ("movl %%ebp, %0" : "=r" (ebp) : );
        } else {
                /* ebp is the last reg pushed by switch_to */
                ebp = *(unsigned long *) task->thread.esp;
        }

        while (1) {
                struct thread_info *context;
                context = (struct thread_info *)
                        ((unsigned long)stack & (~(THREAD_SIZE - 1)));
                ebp = print_context_stack(context, stack, ebp);
                stack = (unsigned long*)context->previous_esp;
                if (!stack)
                        break;
                printk(" =======================\n");
        }
}

void show_stack(struct task_struct *task, unsigned long *esp)
{
        unsigned long *stack;
        int i;

        if (esp == NULL) {
                if (task)
                        esp = (unsigned long*)task->thread.esp;
                else
                        esp = (unsigned long *)&esp;
        }

        stack = esp;
        for(i = 0; i < kstack_depth_to_print; i++) {
                if (kstack_end(stack))
                        break;
                if (i && ((i % 8) == 0))
                        printk("\n       ");
                printk("%08lx ", *stack++);
        }
        printk("\nCall Trace:\n");
        show_trace(task, esp);
}

/*
 * The architecture-independent dump_stack generator
 */
void dump_stack(void)
{
        unsigned long stack;

        show_trace(current, &stack);
}

EXPORT_SYMBOL(dump_stack);

void show_registers(struct pt_regs *regs)
{
        int i;
        int in_kernel = 1;
        unsigned long esp;
        unsigned short ss;

        esp = (unsigned long) (&regs->esp);
        savesegment(ss, ss);
        if (user_mode(regs)) {
                in_kernel = 0;
                esp = regs->esp;
                ss = regs->xss & 0xffff;
        }
        print_modules();
        printk("CPU:    %d\nEIP:    %04x:[<%08lx>]    %s VLI\nEFLAGS: %08lx"
                        "   (%s) \n",
                smp_processor_id(), 0xffff & regs->xcs, regs->eip,
                print_tainted(), regs->eflags, system_utsname.release);
        print_symbol("EIP is at %s\n", regs->eip);
        printk("eax: %08lx   ebx: %08lx   ecx: %08lx   edx: %08lx\n",
                regs->eax, regs->ebx, regs->ecx, regs->edx);
        printk("esi: %08lx   edi: %08lx   ebp: %08lx   esp: %08lx\n",
                regs->esi, regs->edi, regs->ebp, esp);
        printk("ds: %04x   es: %04x   ss: %04x\n",
                regs->xds & 0xffff, regs->xes & 0xffff, ss);
        printk("Process %s (pid: %d, threadinfo=%p task=%p)",
                current->comm, current->pid, current_thread_info(), current);
        /*
         * When in-kernel, we also print out the stack and code at the
         * time of the fault..
         */
        if (in_kernel) {
                u8 __user *eip;

                printk("\nStack: ");
                show_stack(NULL, (unsigned long*)esp);

                printk("Code: ");

                eip = (u8 __user *)regs->eip - 43;
                for (i = 0; i < 64; i++, eip++) {
                        unsigned char c;

                        if (eip < (u8 __user *)PAGE_OFFSET || __get_user(c, eip)) {
                                printk(" Bad EIP value.");
                                break;
                        }
                        if (eip == (u8 __user *)regs->eip)
                                printk("<%02x> ", c);
                        else
                                printk("%02x ", c);
                }
        }
        printk("\n");
}       

static void handle_BUG(struct pt_regs *regs)
{
        unsigned short ud2;
        unsigned short line;
        char *file;
        char c;
        unsigned long eip;

        eip = regs->eip;

        if (eip < PAGE_OFFSET)
                goto no_bug;
        if (__get_user(ud2, (unsigned short __user *)eip))
                goto no_bug;
        if (ud2 != 0x0b0f)
                goto no_bug;
        if (__get_user(line, (unsigned short __user *)(eip + 2)))
                goto bug;
        if (__get_user(file, (char * __user *)(eip + 4)) ||
                (unsigned long)file < PAGE_OFFSET || __get_user(c, file))
                file = "<bad filename>";

        printk("------------[ cut here ]------------\n");
        printk(KERN_ALERT "kernel BUG at %s:%d!\n", file, line);

no_bug:
        return;

        /* Here we know it was a BUG but file-n-line is unavailable */
bug:
        printk("Kernel BUG\n");
}

/* This is gone through when something in the kernel
 * has done something bad and is about to be terminated.
*/
void die(const char * str, struct pt_regs * regs, long err)
{
        static struct {
                spinlock_t lock;
                u32 lock_owner;
                int lock_owner_depth;
        } die = {
                .lock =                 SPIN_LOCK_UNLOCKED,
                .lock_owner =           -1,
                .lock_owner_depth =     0
        };
        static int die_counter;

        if (die.lock_owner != raw_smp_processor_id()) {
                console_verbose();
                spin_lock_irq(&die.lock);
                die.lock_owner = smp_processor_id();
                die.lock_owner_depth = 0;
                bust_spinlocks(1);
        }

        if (++die.lock_owner_depth < 3) {
                int nl = 0;
                handle_BUG(regs);
                printk(KERN_ALERT "%s: %04lx [#%d]\n", str, err & 0xffff, ++die_counter);
#ifdef CONFIG_PREEMPT
                printk("PREEMPT ");
                nl = 1;
#endif
#ifdef CONFIG_SMP
                printk("SMP ");
                nl = 1;
#endif
#ifdef CONFIG_DEBUG_PAGEALLOC
                printk("DEBUG_PAGEALLOC");
                nl = 1;
#endif
                if (nl)
                        printk("\n");
        notify_die(DIE_OOPS, (char *)str, regs, err, 255, SIGSEGV);
                show_registers(regs);
        } else
                printk(KERN_ERR "Recursive die() failure, output suppressed\n");

        bust_spinlocks(0);
        die.lock_owner = -1;
        spin_unlock_irq(&die.lock);

        if (kexec_should_crash(current))
                crash_kexec(regs);

        if (in_interrupt())
                panic("Fatal exception in interrupt");

        if (panic_on_oops) {
                printk(KERN_EMERG "Fatal exception: panic in 5 seconds\n");
                ssleep(5);
                panic("Fatal exception");
        }
        do_exit(SIGSEGV);
}

static inline void die_if_kernel(const char * str, struct pt_regs * regs, long err)
{
        if (!user_mode_vm(regs))
                die(str, regs, err);
}

static void do_trap(int trapnr, int signr, char *str, int vm86,
                           struct pt_regs * regs, long error_code, siginfo_t *info)
{
        struct task_struct *tsk = current;
        tsk->thread.error_code = error_code;
        tsk->thread.trap_no = trapnr;

        if (regs->eflags & VM_MASK) {
                if (vm86)
                        goto vm86_trap;
                goto trap_signal;
        }

        if (!user_mode(regs))
                goto kernel_trap;

        trap_signal: {
                if (info)
                        force_sig_info(signr, info, tsk);
                else
                        force_sig(signr, tsk);
                return;
        }

        kernel_trap: {
                if (!fixup_exception(regs))
                        die(str, regs, error_code);
                return;
        }

        vm86_trap: {
                int ret = handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, trapnr);
                if (ret) goto trap_signal;
                return;
        }
}

#define DO_ERROR(trapnr, signr, str, name) \
fastcall void do_##name(struct pt_regs * regs, long error_code) \
{ \
        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                == NOTIFY_STOP) \
                return; \
        do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
}

#define DO_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
fastcall void do_##name(struct pt_regs * regs, long error_code) \
{ \
        siginfo_t info; \
        info.si_signo = signr; \
        info.si_errno = 0; \
        info.si_code = sicode; \
        info.si_addr = (void __user *)siaddr; \
        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                == NOTIFY_STOP) \
                return; \
        do_trap(trapnr, signr, str, 0, regs, error_code, &info); \
}

#define DO_VM86_ERROR(trapnr, signr, str, name) \
fastcall void do_##name(struct pt_regs * regs, long error_code) \
{ \
        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                == NOTIFY_STOP) \
                return; \
        do_trap(trapnr, signr, str, 1, regs, error_code, NULL); \
}

#define DO_VM86_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
fastcall void do_##name(struct pt_regs * regs, long error_code) \
{ \
        siginfo_t info; \
        info.si_signo = signr; \
        info.si_errno = 0; \
        info.si_code = sicode; \
        info.si_addr = (void __user *)siaddr; \
        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                == NOTIFY_STOP) \
                return; \
        do_trap(trapnr, signr, str, 1, regs, error_code, &info); \
}

DO_VM86_ERROR_INFO( 0, SIGFPE,  "divide error", divide_error, FPE_INTDIV, regs->eip)
#ifndef CONFIG_KPROBES
DO_VM86_ERROR( 3, SIGTRAP, "int3", int3)
#endif
DO_VM86_ERROR( 4, SIGSEGV, "overflow", overflow)
DO_VM86_ERROR( 5, SIGSEGV, "bounds", bounds)
DO_ERROR_INFO( 6, SIGILL,  "invalid operand", invalid_op, ILL_ILLOPN, regs->eip)
DO_ERROR( 9, SIGFPE,  "coprocessor segment overrun", coprocessor_segment_overrun)
DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
DO_ERROR_INFO(32, SIGSEGV, "iret exception", iret_error, ILL_BADSTK, 0)

fastcall void do_general_protection(struct pt_regs * regs, long error_code)
{
        int cpu = get_cpu();
        struct tss_struct *tss = &per_cpu(init_tss, cpu);
        struct thread_struct *thread = &current->thread;

        /*
         * Perform the lazy TSS's I/O bitmap copy. If the TSS has an
         * invalid offset set (the LAZY one) and the faulting thread has
         * a valid I/O bitmap pointer, we copy the I/O bitmap in the TSS
         * and we set the offset field correctly. Then we let the CPU to
         * restart the faulting instruction.
         */
        if (tss->io_bitmap_base == INVALID_IO_BITMAP_OFFSET_LAZY &&
            thread->io_bitmap_ptr) {
                memcpy(tss->io_bitmap, thread->io_bitmap_ptr,
                       thread->io_bitmap_max);
                /*
                 * If the previously set map was extending to higher ports
                 * than the current one, pad extra space with 0xff (no access).
                 */
                if (thread->io_bitmap_max < tss->io_bitmap_max)
                        memset((char *) tss->io_bitmap +
                                thread->io_bitmap_max, 0xff,
                                tss->io_bitmap_max - thread->io_bitmap_max);
                tss->io_bitmap_max = thread->io_bitmap_max;
                tss->io_bitmap_base = IO_BITMAP_OFFSET;
                put_cpu();
                return;
        }
        put_cpu();

        current->thread.error_code = error_code;
        current->thread.trap_no = 13;

        if (regs->eflags & VM_MASK)
                goto gp_in_vm86;

        if (!user_mode(regs))
                goto gp_in_kernel;

        current->thread.error_code = error_code;
        current->thread.trap_no = 13;
        force_sig(SIGSEGV, current);
        return;

gp_in_vm86:
        local_irq_enable();
        handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
        return;

gp_in_kernel:
        if (!fixup_exception(regs)) {
                if (notify_die(DIE_GPF, "general protection fault", regs,
                                error_code, 13, SIGSEGV) == NOTIFY_STOP)
                        return;
                die("general protection fault", regs, error_code);
        }
}

static void mem_parity_error(unsigned char reason, struct pt_regs * regs)
{
        printk("Uhhuh. NMI received. Dazed and confused, but trying to continue\n");
        printk("You probably have a hardware problem with your RAM chips\n");

        /* Clear and disable the memory parity error line. */
        clear_mem_error(reason);
}

static void io_check_error(unsigned char reason, struct pt_regs * regs)
{
        unsigned long i;

        printk("NMI: IOCK error (debug interrupt?)\n");
        show_registers(regs);

        /* Re-enable the IOCK line, wait for a few seconds */
        reason = (reason & 0xf) | 8;
        outb(reason, 0x61);
        i = 2000;
        while (--i) udelay(1000);
        reason &= ~8;
        outb(reason, 0x61);
}

static void unknown_nmi_error(unsigned char reason, struct pt_regs * regs)
{
#ifdef CONFIG_MCA
        /* Might actually be able to figure out what the guilty party
        * is. */
        if( MCA_bus ) {
                mca_handle_nmi();
                return;
        }
#endif
        printk("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
                reason, smp_processor_id());
        printk("Dazed and confused, but trying to continue\n");
        printk("Do you have a strange power saving mode enabled?\n");
}

static DEFINE_SPINLOCK(nmi_print_lock);

void die_nmi (struct pt_regs *regs, const char *msg)
{
        spin_lock(&nmi_print_lock);
        /*
        * We are in trouble anyway, lets at least try
        * to get a message out.
        */
        bust_spinlocks(1);
        printk(msg);
        printk(" on CPU%d, eip %08lx, registers:\n",
                smp_processor_id(), regs->eip);
        show_registers(regs);
        printk("console shuts up ...\n");
        console_silent();
        spin_unlock(&nmi_print_lock);
        bust_spinlocks(0);

        /* If we are in kernel we are probably nested up pretty bad
         * and might aswell get out now while we still can.
        */
        if (!user_mode(regs)) {
                current->thread.trap_no = 2;
                crash_kexec(regs);
        }

        do_exit(SIGSEGV);
}

static void default_do_nmi(struct pt_regs * regs)
{
        unsigned char reason = 0;

        /* Only the BSP gets external NMIs from the system.  */
        if (!smp_processor_id())
                reason = get_nmi_reason();
 
        if (!(reason & 0xc0)) {
                if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 0, SIGINT)
                                                        == NOTIFY_STOP)
                        return;
#ifdef CONFIG_X86_LOCAL_APIC
                /*
                 * Ok, so this is none of the documented NMI sources,
                 * so it must be the NMI watchdog.
                 */
                if (nmi_watchdog) {
                        nmi_watchdog_tick(regs);
                        return;
                }
#endif
                unknown_nmi_error(reason, regs);
                return;
        }
        if (notify_die(DIE_NMI, "nmi", regs, reason, 0, SIGINT) == NOTIFY_STOP)
                return;
        if (reason & 0x80)
                mem_parity_error(reason, regs);
        if (reason & 0x40)
                io_check_error(reason, regs);
        /*
         * Reassert NMI in case it became active meanwhile
         * as it's edge-triggered.
         */
        reassert_nmi();
}

static int dummy_nmi_callback(struct pt_regs * regs, int cpu)
{
        return 0;
}
 
static nmi_callback_t nmi_callback = dummy_nmi_callback;
 
fastcall void do_nmi(struct pt_regs * regs, long error_code)
{
        int cpu;

        nmi_enter();

        cpu = smp_processor_id();

#ifdef CONFIG_HOTPLUG_CPU
        if (!cpu_online(cpu)) {
                nmi_exit();
                return;
        }
#endif

        ++nmi_count(cpu);

        if (!nmi_callback(regs, cpu))
                default_do_nmi(regs);

        nmi_exit();
}

void set_nmi_callback(nmi_callback_t callback)
{
        nmi_callback = callback;
}
EXPORT_SYMBOL_GPL(set_nmi_callback);

void unset_nmi_callback(void)
{
        nmi_callback = dummy_nmi_callback;
}
EXPORT_SYMBOL_GPL(unset_nmi_callback);

#ifdef CONFIG_KPROBES
fastcall void do_int3(struct pt_regs *regs, long error_code)
{
        if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)
                        == NOTIFY_STOP)
                return;
        /* This is an interrupt gate, because kprobes wants interrupts
        disabled.  Normal trap handlers don't. */
        restore_interrupts(regs);
        do_trap(3, SIGTRAP, "int3", 1, regs, error_code, NULL);
}
#endif

/*
 * Our handling of the processor debug registers is non-trivial.
 * We do not clear them on entry and exit from the kernel. Therefore
 * it is possible to get a watchpoint trap here from inside the kernel.
 * However, the code in ./ptrace.c has ensured that the user can
 * only set watchpoints on userspace addresses. Therefore the in-kernel
 * watchpoint trap can only occur in code which is reading/writing
 * from user space. Such code must not hold kernel locks (since it
 * can equally take a page fault), therefore it is safe to call
 * force_sig_info even though that claims and releases locks.
 * 
 * Code in ./signal.c ensures that the debug control register
 * is restored before we deliver any signal, and therefore that
 * user code runs with the correct debug control register even though
 * we clear it here.
 *
 * Being careful here means that we don't have to be as careful in a
 * lot of more complicated places (task switching can be a bit lazy
 * about restoring all the debug state, and ptrace doesn't have to
 * find every occurrence of the TF bit that could be saved away even
 * by user code)
 */
fastcall void do_debug(struct pt_regs * regs, long error_code)
{
        unsigned int condition;
        struct task_struct *tsk = current;

        get_debugreg(condition, 6);

        if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
                                        SIGTRAP) == NOTIFY_STOP)
                return;
        /* It's safe to allow irq's after DR6 has been saved */
        if (regs->eflags & X86_EFLAGS_IF)
                local_irq_enable();

        /* Mask out spurious debug traps due to lazy DR7 setting */
        if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
                if (!tsk->thread.debugreg[7])
                        goto clear_dr7;
        }

        if (regs->eflags & VM_MASK)
                goto debug_vm86;

        /* Save debug status register where ptrace can see it */
        tsk->thread.debugreg[6] = condition;

        /*
         * Single-stepping through TF: make sure we ignore any events in
         * kernel space (but re-enable TF when returning to user mode).
         */
        if (condition & DR_STEP) {
                /*
                 * We already checked v86 mode above, so we can
                 * check for kernel mode by just checking the CPL
                 * of CS.
                 */
                if (!user_mode(regs))
                        goto clear_TF_reenable;
        }

        /* Ok, finally something we can handle */
        send_sigtrap(tsk, regs, error_code);

        /* Disable additional traps. They'll be re-enabled when
         * the signal is delivered.
         */
clear_dr7:
        set_debugreg(0, 7);
        return;

debug_vm86:
        handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
        return;

clear_TF_reenable:
        set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
        regs->eflags &= ~TF_MASK;
        return;
}

/*
 * Note that we play around with the 'TS' bit in an attempt to get
 * the correct behaviour even in the presence of the asynchronous
 * IRQ13 behaviour
 */
void math_error(void __user *eip)
{
        struct task_struct * task;
        siginfo_t info;
        unsigned short cwd, swd;

        /*
         * Save the info for the exception handler and clear the error.
         */
        task = current;
        save_init_fpu(task);
        task->thread.trap_no = 16;
        task->thread.error_code = 0;
        info.si_signo = SIGFPE;
        info.si_errno = 0;
        info.si_code = __SI_FAULT;
        info.si_addr = eip;
        /*
         * (~cwd & swd) will mask out exceptions that are not set to unmasked
         * status.  0x3f is the exception bits in these regs, 0x200 is the
         * C1 reg you need in case of a stack fault, 0x040 is the stack
         * fault bit.  We should only be taking one exception at a time,
         * so if this combination doesn't produce any single exception,
         * then we have a bad program that isn't syncronizing its FPU usage
         * and it will suffer the consequences since we won't be able to
         * fully reproduce the context of the exception
         */
        cwd = get_fpu_cwd(task);
        swd = get_fpu_swd(task);
        switch (swd & ~cwd & 0x3f) {
                case 0x000:
                default:
                        break;
                case 0x001: /* Invalid Op */
                        /*
                         * swd & 0x240 == 0x040: Stack Underflow
                         * swd & 0x240 == 0x240: Stack Overflow
                         * User must clear the SF bit (0x40) if set
                         */
                        info.si_code = FPE_FLTINV;
                        break;
                case 0x002: /* Denormalize */
                case 0x010: /* Underflow */
                        info.si_code = FPE_FLTUND;
                        break;
                case 0x004: /* Zero Divide */
                        info.si_code = FPE_FLTDIV;
                        break;
                case 0x008: /* Overflow */
                        info.si_code = FPE_FLTOVF;
                        break;
                case 0x020: /* Precision */
                        info.si_code = FPE_FLTRES;
                        break;
        }
        force_sig_info(SIGFPE, &info, task);
}

fastcall void do_coprocessor_error(struct pt_regs * regs, long error_code)
{
        ignore_fpu_irq = 1;
        math_error((void __user *)regs->eip);
}

static void simd_math_error(void __user *eip)
{
        struct task_struct * task;
        siginfo_t info;
        unsigned short mxcsr;

        /*
         * Save the info for the exception handler and clear the error.
         */
        task = current;
        save_init_fpu(task);
        task->thread.trap_no = 19;
        task->thread.error_code = 0;
        info.si_signo = SIGFPE;
        info.si_errno = 0;
        info.si_code = __SI_FAULT;
        info.si_addr = eip;
        /*
         * The SIMD FPU exceptions are handled a little differently, as there
         * is only a single status/control register.  Thus, to determine which
         * unmasked exception was caught we must mask the exception mask bits
         * at 0x1f80, and then use these to mask the exception bits at 0x3f.
         */
        mxcsr = get_fpu_mxcsr(task);
        switch (~((mxcsr & 0x1f80) >> 7) & (mxcsr & 0x3f)) {
                case 0x000:
                default:
                        break;
                case 0x001: /* Invalid Op */
                        info.si_code = FPE_FLTINV;
                        break;
                case 0x002: /* Denormalize */
                case 0x010: /* Underflow */
                        info.si_code = FPE_FLTUND;
                        break;
                case 0x004: /* Zero Divide */
                        info.si_code = FPE_FLTDIV;
                        break;
                case 0x008: /* Overflow */
                        info.si_code = FPE_FLTOVF;
                        break;
                case 0x020: /* Precision */
                        info.si_code = FPE_FLTRES;
                        break;
        }
        force_sig_info(SIGFPE, &info, task);
}

fastcall void do_simd_coprocessor_error(struct pt_regs * regs,
                                          long error_code)
{
        if (cpu_has_xmm) {
                /* Handle SIMD FPU exceptions on PIII+ processors. */
                ignore_fpu_irq = 1;
                simd_math_error((void __user *)regs->eip);
        } else {
                /*
                 * Handle strange cache flush from user space exception
                 * in all other cases.  This is undocumented behaviour.
                 */
                if (regs->eflags & VM_MASK) {
                        handle_vm86_fault((struct kernel_vm86_regs *)regs,
                                          error_code);
                        return;
                }
                current->thread.trap_no = 19;
                current->thread.error_code = error_code;
                die_if_kernel("cache flush denied", regs, error_code);
                force_sig(SIGSEGV, current);
        }
}

fastcall void do_spurious_interrupt_bug(struct pt_regs * regs,
                                          long error_code)
{
#if 0
        /* No need to warn about this any longer. */
        printk("Ignoring P6 Local APIC Spurious Interrupt Bug...\n");
#endif
}

fastcall void setup_x86_bogus_stack(unsigned char * stk)
{
        unsigned long *switch16_ptr, *switch32_ptr;
        struct pt_regs *regs;
        unsigned long stack_top, stack_bot;
        unsigned short iret_frame16_off;
        int cpu = smp_processor_id();
        /* reserve the space on 32bit stack for the magic switch16 pointer */
        memmove(stk, stk + 8, sizeof(struct pt_regs));
        switch16_ptr = (unsigned long *)(stk + sizeof(struct pt_regs));
        regs = (struct pt_regs *)stk;
        /* now the switch32 on 16bit stack */
        stack_bot = (unsigned long)&per_cpu(cpu_16bit_stack, cpu);
        stack_top = stack_bot + CPU_16BIT_STACK_SIZE;
        switch32_ptr = (unsigned long *)(stack_top - 8);
        iret_frame16_off = CPU_16BIT_STACK_SIZE - 8 - 20;
        /* copy iret frame on 16bit stack */
        memcpy((void *)(stack_bot + iret_frame16_off), &regs->eip, 20);
        /* fill in the switch pointers */
        switch16_ptr[0] = (regs->esp & 0xffff0000) | iret_frame16_off;
        switch16_ptr[1] = __ESPFIX_SS;
        switch32_ptr[0] = (unsigned long)stk + sizeof(struct pt_regs) +
                8 - CPU_16BIT_STACK_SIZE;
        switch32_ptr[1] = __KERNEL_DS;
}

fastcall unsigned char * fixup_x86_bogus_stack(unsigned short sp)
{
        unsigned long *switch32_ptr;
        unsigned char *stack16, *stack32;
        unsigned long stack_top, stack_bot;
        int len;
        int cpu = smp_processor_id();
        stack_bot = (unsigned long)&per_cpu(cpu_16bit_stack, cpu);
        stack_top = stack_bot + CPU_16BIT_STACK_SIZE;
        switch32_ptr = (unsigned long *)(stack_top - 8);
        /* copy the data from 16bit stack to 32bit stack */
        len = CPU_16BIT_STACK_SIZE - 8 - sp;
        stack16 = (unsigned char *)(stack_bot + sp);
        stack32 = (unsigned char *)
                (switch32_ptr[0] + CPU_16BIT_STACK_SIZE - 8 - len);
        memcpy(stack32, stack16, len);
        return stack32;
}

/*
 *  'math_state_restore()' saves the current math information in the
 * old math state array, and gets the new ones from the current task
 *
 * Careful.. There are problems with IBM-designed IRQ13 behaviour.
 * Don't touch unless you *really* know how it works.
 *
 * Must be called with kernel preemption disabled (in this case,
 * local interrupts are disabled at the call-site in entry.S).
 */
asmlinkage void math_state_restore(struct pt_regs regs)
{
        struct thread_info *thread = current_thread_info();
        struct task_struct *tsk = thread->task;

        clts();         /* Allow maths ops (or we recurse) */
        if (!tsk_used_math(tsk))
                init_fpu(tsk);
        restore_fpu(tsk);
        thread->status |= TS_USEDFPU;   /* So we fnsave on switch_to() */
}

#ifndef CONFIG_MATH_EMULATION

asmlinkage void math_emulate(long arg)
{
        printk("math-emulation not enabled and no coprocessor found.\n");
        printk("killing %s.\n",current->comm);
        force_sig(SIGFPE,current);
        schedule();
}

#endif /* CONFIG_MATH_EMULATION */

#ifdef CONFIG_X86_F00F_BUG
void __init trap_init_f00f_bug(void)
{
        __set_fixmap(FIX_F00F_IDT, __pa(&idt_table), PAGE_KERNEL_RO);

        /*
         * Update the IDT descriptor and reload the IDT so that
         * it uses the read-only mapped virtual address.
         */
        idt_descr.address = fix_to_virt(FIX_F00F_IDT);
        load_idt(&idt_descr);
}
#endif

#define _set_gate(gate_addr,type,dpl,addr,seg) \
do { \
  int __d0, __d1; \
  __asm__ __volatile__ ("movw %%dx,%%ax\n\t" \
        "movw %4,%%dx\n\t" \
        "movl %%eax,%0\n\t" \
        "movl %%edx,%1" \
        :"=m" (*((long *) (gate_addr))), \
         "=m" (*(1+(long *) (gate_addr))), "=&a" (__d0), "=&d" (__d1) \
        :"i" ((short) (0x8000+(dpl<<13)+(type<<8))), \
         "3" ((char *) (addr)),"2" ((seg) << 16)); \
} while (0)


/*
 * This needs to use 'idt_table' rather than 'idt', and
 * thus use the _nonmapped_ version of the IDT, as the
 * Pentium F0 0F bugfix can have resulted in the mapped
 * IDT being write-protected.
 */
void set_intr_gate(unsigned int n, void *addr)
{
        _set_gate(idt_table+n,14,0,addr,__KERNEL_CS);
}

/*
 * This routine sets up an interrupt gate at directory privilege level 3.
 */
static inline void set_system_intr_gate(unsigned int n, void *addr)
{
        _set_gate(idt_table+n, 14, 3, addr, __KERNEL_CS);
}

static void __init set_trap_gate(unsigned int n, void *addr)
{
        _set_gate(idt_table+n,15,0,addr,__KERNEL_CS);
}

static void __init set_system_gate(unsigned int n, void *addr)
{
        _set_gate(idt_table+n,15,3,addr,__KERNEL_CS);
}

static void __init set_task_gate(unsigned int n, unsigned int gdt_entry)
{
        _set_gate(idt_table+n,5,0,0,(gdt_entry<<3));
}


void __init trap_init(void)
{
#ifdef CONFIG_EISA
        void __iomem *p = ioremap(0x0FFFD9, 4);
        if (readl(p) == 'E'+('I'<<8)+('S'<<16)+('A'<<24)) {
                EISA_bus = 1;
        }
        iounmap(p);
#endif

#ifdef CONFIG_X86_LOCAL_APIC
        init_apic_mappings();
#endif

        set_trap_gate(0,&divide_error);
        set_intr_gate(1,&debug);
        set_intr_gate(2,&nmi);
        set_system_intr_gate(3, &int3); /* int3-5 can be called from all */
        set_system_gate(4,&overflow);
        set_system_gate(5,&bounds);
        set_trap_gate(6,&invalid_op);
        set_trap_gate(7,&device_not_available);
        set_task_gate(8,GDT_ENTRY_DOUBLEFAULT_TSS);
        set_trap_gate(9,&coprocessor_segment_overrun);
        set_trap_gate(10,&invalid_TSS);
        set_trap_gate(11,&segment_not_present);
        set_trap_gate(12,&stack_segment);
        set_trap_gate(13,&general_protection);
        set_intr_gate(14,&page_fault);
        set_trap_gate(15,&spurious_interrupt_bug);
        set_trap_gate(16,&coprocessor_error);
        set_trap_gate(17,&alignment_check);
#ifdef CONFIG_X86_MCE
        set_trap_gate(18,&machine_check);
#endif
        set_trap_gate(19,&simd_coprocessor_error);

        set_system_gate(SYSCALL_VECTOR,&system_call);

        /*
         * Should be a barrier for any external CPU state.
         */
        cpu_init();

        trap_init_hook();
}

static int __init kstack_setup(char *s)
{
        kstack_depth_to_print = simple_strtoul(s, NULL, 0);
        return 0;
}
__setup("kstack=", kstack_setup);