[PATCH] i386: reliable stack trace support (i386)

[wrt350n-kernel.git] / arch / i386 / kernel / process.c

/*
 *  linux/arch/i386/kernel/process.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */

/*
 * This file handles the architecture-dependent parts of process handling..
 */

#include <stdarg.h>

#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/elfcore.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/user.h>
#include <linux/a.out.h>
#include <linux/interrupt.h>
#include <linux/config.h>
#include <linux/utsname.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/mc146818rtc.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/ptrace.h>
#include <linux/random.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/ldt.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/desc.h>
#include <asm/vm86.h>
#ifdef CONFIG_MATH_EMULATION
#include <asm/math_emu.h>
#endif

#include <linux/err.h>

#include <asm/tlbflush.h>
#include <asm/cpu.h>

asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");

static int hlt_counter;

unsigned long boot_option_idle_override = 0;
EXPORT_SYMBOL(boot_option_idle_override);

/*
 * Return saved PC of a blocked thread.
 */
unsigned long thread_saved_pc(struct task_struct *tsk)
{
        return ((unsigned long *)tsk->thread.esp)[3];
}

/*
 * Powermanagement idle function, if any..
 */
void (*pm_idle)(void);
EXPORT_SYMBOL(pm_idle);
static DEFINE_PER_CPU(unsigned int, cpu_idle_state);

void disable_hlt(void)
{
        hlt_counter++;
}

EXPORT_SYMBOL(disable_hlt);

void enable_hlt(void)
{
        hlt_counter--;
}

EXPORT_SYMBOL(enable_hlt);

/*
 * We use this if we don't have any better
 * idle routine..
 */
void default_idle(void)
{
        local_irq_enable();

        if (!hlt_counter && boot_cpu_data.hlt_works_ok) {
                clear_thread_flag(TIF_POLLING_NRFLAG);
                smp_mb__after_clear_bit();
                while (!need_resched()) {
                        local_irq_disable();
                        if (!need_resched())
                                safe_halt();
                        else
                                local_irq_enable();
                }
                set_thread_flag(TIF_POLLING_NRFLAG);
        } else {
                while (!need_resched())
                        cpu_relax();
        }
}
#ifdef CONFIG_APM_MODULE
EXPORT_SYMBOL(default_idle);
#endif

/*
 * On SMP it's slightly faster (but much more power-consuming!)
 * to poll the ->work.need_resched flag instead of waiting for the
 * cross-CPU IPI to arrive. Use this option with caution.
 */
static void poll_idle (void)
{
        local_irq_enable();

        asm volatile(
                "2:"
                "testl %0, %1;"
                "rep; nop;"
                "je 2b;"
                : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags));
}

#ifdef CONFIG_HOTPLUG_CPU
#include <asm/nmi.h>
/* We don't actually take CPU down, just spin without interrupts. */
static inline void play_dead(void)
{
        /* This must be done before dead CPU ack */
        cpu_exit_clear();
        wbinvd();
        mb();
        /* Ack it */
        __get_cpu_var(cpu_state) = CPU_DEAD;

        /*
         * With physical CPU hotplug, we should halt the cpu
         */
        local_irq_disable();
        while (1)
                halt();
}
#else
static inline void play_dead(void)
{
        BUG();
}
#endif /* CONFIG_HOTPLUG_CPU */

/*
 * The idle thread. There's no useful work to be
 * done, so just try to conserve power and have a
 * low exit latency (ie sit in a loop waiting for
 * somebody to say that they'd like to reschedule)
 */
void cpu_idle(void)
{
        int cpu = smp_processor_id();

        set_thread_flag(TIF_POLLING_NRFLAG);

        /* endless idle loop with no priority at all */
        while (1) {
                while (!need_resched()) {
                        void (*idle)(void);

                        if (__get_cpu_var(cpu_idle_state))
                                __get_cpu_var(cpu_idle_state) = 0;

                        rmb();
                        idle = pm_idle;

                        if (!idle)
                                idle = default_idle;

                        if (cpu_is_offline(cpu))
                                play_dead();

                        __get_cpu_var(irq_stat).idle_timestamp = jiffies;
                        idle();
                }
                preempt_enable_no_resched();
                schedule();
                preempt_disable();
        }
}

void cpu_idle_wait(void)
{
        unsigned int cpu, this_cpu = get_cpu();
        cpumask_t map;

        set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
        put_cpu();

        cpus_clear(map);
        for_each_online_cpu(cpu) {
                per_cpu(cpu_idle_state, cpu) = 1;
                cpu_set(cpu, map);
        }

        __get_cpu_var(cpu_idle_state) = 0;

        wmb();
        do {
                ssleep(1);
                for_each_online_cpu(cpu) {
                        if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
                                cpu_clear(cpu, map);
                }
                cpus_and(map, map, cpu_online_map);
        } while (!cpus_empty(map));
}
EXPORT_SYMBOL_GPL(cpu_idle_wait);

/*
 * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
 * which can obviate IPI to trigger checking of need_resched.
 * We execute MONITOR against need_resched and enter optimized wait state
 * through MWAIT. Whenever someone changes need_resched, we would be woken
 * up from MWAIT (without an IPI).
 */
static void mwait_idle(void)
{
        local_irq_enable();

        while (!need_resched()) {
                __monitor((void *)&current_thread_info()->flags, 0, 0);
                smp_mb();
                if (need_resched())
                        break;
                __mwait(0, 0);
        }
}

void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
{
        if (cpu_has(c, X86_FEATURE_MWAIT)) {
                printk("monitor/mwait feature present.\n");
                /*
                 * Skip, if setup has overridden idle.
                 * One CPU supports mwait => All CPUs supports mwait
                 */
                if (!pm_idle) {
                        printk("using mwait in idle threads.\n");
                        pm_idle = mwait_idle;
                }
        }
}

static int __init idle_setup (char *str)
{
        if (!strncmp(str, "poll", 4)) {
                printk("using polling idle threads.\n");
                pm_idle = poll_idle;
#ifdef CONFIG_X86_SMP
                if (smp_num_siblings > 1)
                        printk("WARNING: polling idle and HT enabled, performance may degrade.\n");
#endif
        } else if (!strncmp(str, "halt", 4)) {
                printk("using halt in idle threads.\n");
                pm_idle = default_idle;
        }

        boot_option_idle_override = 1;
        return 1;
}

__setup("idle=", idle_setup);

void show_regs(struct pt_regs * regs)
{
        unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;

        printk("\n");
        printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
        printk("EIP: %04x:[<%08lx>] CPU: %d\n",0xffff & regs->xcs,regs->eip, smp_processor_id());
        print_symbol("EIP is at %s\n", regs->eip);

        if (user_mode_vm(regs))
                printk(" ESP: %04x:%08lx",0xffff & regs->xss,regs->esp);
        printk(" EFLAGS: %08lx    %s  (%s %.*s)\n",
               regs->eflags, print_tainted(), system_utsname.release,
               (int)strcspn(system_utsname.version, " "),
               system_utsname.version);
        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",
                regs->esi, regs->edi, regs->ebp);
        printk(" DS: %04x ES: %04x\n",
                0xffff & regs->xds,0xffff & regs->xes);

        cr0 = read_cr0();
        cr2 = read_cr2();
        cr3 = read_cr3();
        cr4 = read_cr4_safe();
        printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n", cr0, cr2, cr3, cr4);
        show_trace(NULL, regs, &regs->esp);
}

/*
 * This gets run with %ebx containing the
 * function to call, and %edx containing
 * the "args".
 */
extern void kernel_thread_helper(void);
__asm__(".section .text\n"
        ".align 4\n"
        "kernel_thread_helper:\n\t"
        "movl %edx,%eax\n\t"
        "pushl %edx\n\t"
        "call *%ebx\n\t"
        "pushl %eax\n\t"
        "call do_exit\n"
        ".previous");

/*
 * Create a kernel thread
 */
int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
{
        struct pt_regs regs;

        memset(&regs, 0, sizeof(regs));

        regs.ebx = (unsigned long) fn;
        regs.edx = (unsigned long) arg;

        regs.xds = __USER_DS;
        regs.xes = __USER_DS;
        regs.orig_eax = -1;
        regs.eip = (unsigned long) kernel_thread_helper;
        regs.xcs = __KERNEL_CS;
        regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;

        /* Ok, create the new process.. */
        return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
}
EXPORT_SYMBOL(kernel_thread);

/*
 * Free current thread data structures etc..
 */
void exit_thread(void)
{
        struct task_struct *tsk = current;
        struct thread_struct *t = &tsk->thread;

        /* The process may have allocated an io port bitmap... nuke it. */
        if (unlikely(NULL != t->io_bitmap_ptr)) {
                int cpu = get_cpu();
                struct tss_struct *tss = &per_cpu(init_tss, cpu);

                kfree(t->io_bitmap_ptr);
                t->io_bitmap_ptr = NULL;
                /*
                 * Careful, clear this in the TSS too:
                 */
                memset(tss->io_bitmap, 0xff, tss->io_bitmap_max);
                t->io_bitmap_max = 0;
                tss->io_bitmap_owner = NULL;
                tss->io_bitmap_max = 0;
                tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
                put_cpu();
        }
}

void flush_thread(void)
{
        struct task_struct *tsk = current;

        memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
        memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));        
        /*
         * Forget coprocessor state..
         */
        clear_fpu(tsk);
        clear_used_math();
}

void release_thread(struct task_struct *dead_task)
{
        BUG_ON(dead_task->mm);
        release_vm86_irqs(dead_task);
}

/*
 * This gets called before we allocate a new thread and copy
 * the current task into it.
 */
void prepare_to_copy(struct task_struct *tsk)
{
        unlazy_fpu(tsk);
}

int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
        unsigned long unused,
        struct task_struct * p, struct pt_regs * regs)
{
        struct pt_regs * childregs;
        struct task_struct *tsk;
        int err;

        childregs = task_pt_regs(p);
        *childregs = *regs;
        childregs->eax = 0;
        childregs->esp = esp;

        p->thread.esp = (unsigned long) childregs;
        p->thread.esp0 = (unsigned long) (childregs+1);

        p->thread.eip = (unsigned long) ret_from_fork;

        savesegment(fs,p->thread.fs);
        savesegment(gs,p->thread.gs);

        tsk = current;
        if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
                p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
                if (!p->thread.io_bitmap_ptr) {
                        p->thread.io_bitmap_max = 0;
                        return -ENOMEM;
                }
                memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
                        IO_BITMAP_BYTES);
        }

        /*
         * Set a new TLS for the child thread?
         */
        if (clone_flags & CLONE_SETTLS) {
                struct desc_struct *desc;
                struct user_desc info;
                int idx;

                err = -EFAULT;
                if (copy_from_user(&info, (void __user *)childregs->esi, sizeof(info)))
                        goto out;
                err = -EINVAL;
                if (LDT_empty(&info))
                        goto out;

                idx = info.entry_number;
                if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                        goto out;

                desc = p->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
                desc->a = LDT_entry_a(&info);
                desc->b = LDT_entry_b(&info);
        }

        err = 0;
 out:
        if (err && p->thread.io_bitmap_ptr) {
                kfree(p->thread.io_bitmap_ptr);
                p->thread.io_bitmap_max = 0;
        }
        return err;
}

/*
 * fill in the user structure for a core dump..
 */
void dump_thread(struct pt_regs * regs, struct user * dump)
{
        int i;

/* changed the size calculations - should hopefully work better. lbt */
        dump->magic = CMAGIC;
        dump->start_code = 0;
        dump->start_stack = regs->esp & ~(PAGE_SIZE - 1);
        dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
        dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
        dump->u_dsize -= dump->u_tsize;
        dump->u_ssize = 0;
        for (i = 0; i < 8; i++)
                dump->u_debugreg[i] = current->thread.debugreg[i];  

        if (dump->start_stack < TASK_SIZE)
                dump->u_ssize = ((unsigned long) (TASK_SIZE - dump->start_stack)) >> PAGE_SHIFT;

        dump->regs.ebx = regs->ebx;
        dump->regs.ecx = regs->ecx;
        dump->regs.edx = regs->edx;
        dump->regs.esi = regs->esi;
        dump->regs.edi = regs->edi;
        dump->regs.ebp = regs->ebp;
        dump->regs.eax = regs->eax;
        dump->regs.ds = regs->xds;
        dump->regs.es = regs->xes;
        savesegment(fs,dump->regs.fs);
        savesegment(gs,dump->regs.gs);
        dump->regs.orig_eax = regs->orig_eax;
        dump->regs.eip = regs->eip;
        dump->regs.cs = regs->xcs;
        dump->regs.eflags = regs->eflags;
        dump->regs.esp = regs->esp;
        dump->regs.ss = regs->xss;

        dump->u_fpvalid = dump_fpu (regs, &dump->i387);
}
EXPORT_SYMBOL(dump_thread);

/* 
 * Capture the user space registers if the task is not running (in user space)
 */
int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
{
        struct pt_regs ptregs = *task_pt_regs(tsk);
        ptregs.xcs &= 0xffff;
        ptregs.xds &= 0xffff;
        ptregs.xes &= 0xffff;
        ptregs.xss &= 0xffff;

        elf_core_copy_regs(regs, &ptregs);

        return 1;
}

static inline void
handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
{
        if (!next->io_bitmap_ptr) {
                /*
                 * Disable the bitmap via an invalid offset. We still cache
                 * the previous bitmap owner and the IO bitmap contents:
                 */
                tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
                return;
        }
        if (likely(next == tss->io_bitmap_owner)) {
                /*
                 * Previous owner of the bitmap (hence the bitmap content)
                 * matches the next task, we dont have to do anything but
                 * to set a valid offset in the TSS:
                 */
                tss->io_bitmap_base = IO_BITMAP_OFFSET;
                return;
        }
        /*
         * Lazy TSS's I/O bitmap copy. We set an invalid offset here
         * and we let the task to get a GPF in case an I/O instruction
         * is performed.  The handler of the GPF will verify that the
         * faulting task has a valid I/O bitmap and, it true, does the
         * real copy and restart the instruction.  This will save us
         * redundant copies when the currently switched task does not
         * perform any I/O during its timeslice.
         */
        tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
}

/*
 * This function selects if the context switch from prev to next
 * has to tweak the TSC disable bit in the cr4.
 */
static inline void disable_tsc(struct task_struct *prev_p,
                               struct task_struct *next_p)
{
        struct thread_info *prev, *next;

        /*
         * gcc should eliminate the ->thread_info dereference if
         * has_secure_computing returns 0 at compile time (SECCOMP=n).
         */
        prev = task_thread_info(prev_p);
        next = task_thread_info(next_p);

        if (has_secure_computing(prev) || has_secure_computing(next)) {
                /* slow path here */
                if (has_secure_computing(prev) &&
                    !has_secure_computing(next)) {
                        write_cr4(read_cr4() & ~X86_CR4_TSD);
                } else if (!has_secure_computing(prev) &&
                           has_secure_computing(next))
                        write_cr4(read_cr4() | X86_CR4_TSD);
        }
}

/*
 *      switch_to(x,yn) should switch tasks from x to y.
 *
 * We fsave/fwait so that an exception goes off at the right time
 * (as a call from the fsave or fwait in effect) rather than to
 * the wrong process. Lazy FP saving no longer makes any sense
 * with modern CPU's, and this simplifies a lot of things (SMP
 * and UP become the same).
 *
 * NOTE! We used to use the x86 hardware context switching. The
 * reason for not using it any more becomes apparent when you
 * try to recover gracefully from saved state that is no longer
 * valid (stale segment register values in particular). With the
 * hardware task-switch, there is no way to fix up bad state in
 * a reasonable manner.
 *
 * The fact that Intel documents the hardware task-switching to
 * be slow is a fairly red herring - this code is not noticeably
 * faster. However, there _is_ some room for improvement here,
 * so the performance issues may eventually be a valid point.
 * More important, however, is the fact that this allows us much
 * more flexibility.
 *
 * The return value (in %eax) will be the "prev" task after
 * the task-switch, and shows up in ret_from_fork in entry.S,
 * for example.
 */
struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
{
        struct thread_struct *prev = &prev_p->thread,
                                 *next = &next_p->thread;
        int cpu = smp_processor_id();
        struct tss_struct *tss = &per_cpu(init_tss, cpu);

        /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */

        __unlazy_fpu(prev_p);

        /*
         * Reload esp0.
         */
        load_esp0(tss, next);

        /*
         * Save away %fs and %gs. No need to save %es and %ds, as
         * those are always kernel segments while inside the kernel.
         * Doing this before setting the new TLS descriptors avoids
         * the situation where we temporarily have non-reloadable
         * segments in %fs and %gs.  This could be an issue if the
         * NMI handler ever used %fs or %gs (it does not today), or
         * if the kernel is running inside of a hypervisor layer.
         */
        savesegment(fs, prev->fs);
        savesegment(gs, prev->gs);

        /*
         * Load the per-thread Thread-Local Storage descriptor.
         */
        load_TLS(next, cpu);

        /*
         * Restore %fs and %gs if needed.
         *
         * Glibc normally makes %fs be zero, and %gs is one of
         * the TLS segments.
         */
        if (unlikely(prev->fs | next->fs))
                loadsegment(fs, next->fs);

        if (prev->gs | next->gs)
                loadsegment(gs, next->gs);

        /*
         * Restore IOPL if needed.
         */
        if (unlikely(prev->iopl != next->iopl))
                set_iopl_mask(next->iopl);

        /*
         * Now maybe reload the debug registers
         */
        if (unlikely(next->debugreg[7])) {
                set_debugreg(next->debugreg[0], 0);
                set_debugreg(next->debugreg[1], 1);
                set_debugreg(next->debugreg[2], 2);
                set_debugreg(next->debugreg[3], 3);
                /* no 4 and 5 */
                set_debugreg(next->debugreg[6], 6);
                set_debugreg(next->debugreg[7], 7);
        }

        if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
                handle_io_bitmap(next, tss);

        disable_tsc(prev_p, next_p);

        return prev_p;
}

asmlinkage int sys_fork(struct pt_regs regs)
{
        return do_fork(SIGCHLD, regs.esp, &regs, 0, NULL, NULL);
}

asmlinkage int sys_clone(struct pt_regs regs)
{
        unsigned long clone_flags;
        unsigned long newsp;
        int __user *parent_tidptr, *child_tidptr;

        clone_flags = regs.ebx;
        newsp = regs.ecx;
        parent_tidptr = (int __user *)regs.edx;
        child_tidptr = (int __user *)regs.edi;
        if (!newsp)
                newsp = regs.esp;
        return do_fork(clone_flags, newsp, &regs, 0, parent_tidptr, child_tidptr);
}

/*
 * This is trivial, and on the face of it looks like it
 * could equally well be done in user mode.
 *
 * Not so, for quite unobvious reasons - register pressure.
 * In user mode vfork() cannot have a stack frame, and if
 * done by calling the "clone()" system call directly, you
 * do not have enough call-clobbered registers to hold all
 * the information you need.
 */
asmlinkage int sys_vfork(struct pt_regs regs)
{
        return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.esp, &regs, 0, NULL, NULL);
}

/*
 * sys_execve() executes a new program.
 */
asmlinkage int sys_execve(struct pt_regs regs)
{
        int error;
        char * filename;

        filename = getname((char __user *) regs.ebx);
        error = PTR_ERR(filename);
        if (IS_ERR(filename))
                goto out;
        error = do_execve(filename,
                        (char __user * __user *) regs.ecx,
                        (char __user * __user *) regs.edx,
                        &regs);
        if (error == 0) {
                task_lock(current);
                current->ptrace &= ~PT_DTRACE;
                task_unlock(current);
                /* Make sure we don't return using sysenter.. */
                set_thread_flag(TIF_IRET);
        }
        putname(filename);
out:
        return error;
}

#define top_esp                (THREAD_SIZE - sizeof(unsigned long))
#define top_ebp                (THREAD_SIZE - 2*sizeof(unsigned long))

unsigned long get_wchan(struct task_struct *p)
{
        unsigned long ebp, esp, eip;
        unsigned long stack_page;
        int count = 0;
        if (!p || p == current || p->state == TASK_RUNNING)
                return 0;
        stack_page = (unsigned long)task_stack_page(p);
        esp = p->thread.esp;
        if (!stack_page || esp < stack_page || esp > top_esp+stack_page)
                return 0;
        /* include/asm-i386/system.h:switch_to() pushes ebp last. */
        ebp = *(unsigned long *) esp;
        do {
                if (ebp < stack_page || ebp > top_ebp+stack_page)
                        return 0;
                eip = *(unsigned long *) (ebp+4);
                if (!in_sched_functions(eip))
                        return eip;
                ebp = *(unsigned long *) ebp;
        } while (count++ < 16);
        return 0;
}

/*
 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
 */
static int get_free_idx(void)
{
        struct thread_struct *t = &current->thread;
        int idx;

        for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
                if (desc_empty(t->tls_array + idx))
                        return idx + GDT_ENTRY_TLS_MIN;
        return -ESRCH;
}

/*
 * Set a given TLS descriptor:
 */
asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
{
        struct thread_struct *t = &current->thread;
        struct user_desc info;
        struct desc_struct *desc;
        int cpu, idx;

        if (copy_from_user(&info, u_info, sizeof(info)))
                return -EFAULT;
        idx = info.entry_number;

        /*
         * index -1 means the kernel should try to find and
         * allocate an empty descriptor:
         */
        if (idx == -1) {
                idx = get_free_idx();
                if (idx < 0)
                        return idx;
                if (put_user(idx, &u_info->entry_number))
                        return -EFAULT;
        }

        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        desc = t->tls_array + idx - GDT_ENTRY_TLS_MIN;

        /*
         * We must not get preempted while modifying the TLS.
         */
        cpu = get_cpu();

        if (LDT_empty(&info)) {
                desc->a = 0;
                desc->b = 0;
        } else {
                desc->a = LDT_entry_a(&info);
                desc->b = LDT_entry_b(&info);
        }
        load_TLS(t, cpu);

        put_cpu();

        return 0;
}

/*
 * Get the current Thread-Local Storage area:
 */

#define GET_BASE(desc) ( \
        (((desc)->a >> 16) & 0x0000ffff) | \
        (((desc)->b << 16) & 0x00ff0000) | \
        ( (desc)->b        & 0xff000000)   )

#define GET_LIMIT(desc) ( \
        ((desc)->a & 0x0ffff) | \
         ((desc)->b & 0xf0000) )
        
#define GET_32BIT(desc)         (((desc)->b >> 22) & 1)
#define GET_CONTENTS(desc)      (((desc)->b >> 10) & 3)
#define GET_WRITABLE(desc)      (((desc)->b >>  9) & 1)
#define GET_LIMIT_PAGES(desc)   (((desc)->b >> 23) & 1)
#define GET_PRESENT(desc)       (((desc)->b >> 15) & 1)
#define GET_USEABLE(desc)       (((desc)->b >> 20) & 1)

asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
{
        struct user_desc info;
        struct desc_struct *desc;
        int idx;

        if (get_user(idx, &u_info->entry_number))
                return -EFAULT;
        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        memset(&info, 0, sizeof(info));

        desc = current->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;

        info.entry_number = idx;
        info.base_addr = GET_BASE(desc);
        info.limit = GET_LIMIT(desc);
        info.seg_32bit = GET_32BIT(desc);
        info.contents = GET_CONTENTS(desc);
        info.read_exec_only = !GET_WRITABLE(desc);
        info.limit_in_pages = GET_LIMIT_PAGES(desc);
        info.seg_not_present = !GET_PRESENT(desc);
        info.useable = GET_USEABLE(desc);

        if (copy_to_user(u_info, &info, sizeof(info)))
                return -EFAULT;
        return 0;
}

unsigned long arch_align_stack(unsigned long sp)
{
        if (randomize_va_space)
                sp -= get_random_int() % 8192;
        return sp & ~0xf;
}