source: trunk/packages/xen-common/xen-common/linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c @ 34

/*
 *  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/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 <xen/interface/physdev.h>
#include <xen/interface/vcpu.h>
#include <xen/cpu_hotplug.h>

#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);

/*
 * 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));
}

static void xen_idle(void)
{
        local_irq_disable();

        if (need_resched())
                local_irq_enable();
        else {
                current_thread_info()->status &= ~TS_POLLING;
                smp_mb__after_clear_bit();
                safe_halt();
                current_thread_info()->status |= TS_POLLING;
        }
}
#ifdef CONFIG_APM_MODULE
EXPORT_SYMBOL(default_idle);
#endif

#ifdef CONFIG_HOTPLUG_CPU
extern cpumask_t cpu_initialized;
static inline void play_dead(void)
{
        idle_task_exit();
        local_irq_disable();
        cpu_clear(smp_processor_id(), cpu_initialized);
        preempt_enable_no_resched();
        HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
        cpu_bringup();
}
#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();

        current_thread_info()->status |= TS_POLLING;

        /* 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 = xen_idle; /* no alternatives */

                        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);

void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
{
}

static int __init idle_setup (char *str)
{
        if (!strncmp(str, "poll", 4)) {
                printk("using polling idle threads.\n");
                pm_idle = poll_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 = GET_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)
{
        /* The process may have allocated an io port bitmap... nuke it. */
        if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
                struct task_struct *tsk = current;
                struct thread_struct *t = &tsk->thread;
                struct physdev_set_iobitmap set_iobitmap;
                memset(&set_iobitmap, 0, sizeof(set_iobitmap));
                HYPERVISOR_physdev_op(PHYSDEVOP_set_iobitmap, &set_iobitmap);
                kfree(t->io_bitmap_ptr);
                t->io_bitmap_ptr = NULL;
                clear_thread_flag(TIF_IO_BITMAP);
        }
}

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));        
        clear_tsk_thread_flag(tsk, TIF_DEBUG);
        /*
         * 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(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
                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_tsk_thread_flag(p, TIF_IO_BITMAP);
        }

        /*
         * 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);
        }

        p->thread.iopl = current->thread.iopl;

        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 noinline void __switch_to_xtra(struct task_struct *next_p)
{
        struct thread_struct *next;

        next = &next_p->thread;

        if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
                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);
        }
}

/*
 * 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();
#ifndef CONFIG_X86_NO_TSS
        struct tss_struct *tss = &per_cpu(init_tss, cpu);
#endif
        struct physdev_set_iopl iopl_op;
        struct physdev_set_iobitmap iobmp_op;
        multicall_entry_t _mcl[8], *mcl = _mcl;

        /* XEN NOTE: FS/GS saved in switch_mm(), not here. */

        /*
         * This is basically '__unlazy_fpu', except that we queue a
         * multicall to indicate FPU task switch, rather than
         * synchronously trapping to Xen.
         */
        if (prev_p->thread_info->status & TS_USEDFPU) {
                __save_init_fpu(prev_p); /* _not_ save_init_fpu() */
                mcl->op      = __HYPERVISOR_fpu_taskswitch;
                mcl->args[0] = 1;
                mcl++;
        }
#if 0 /* lazy fpu sanity check */
        else BUG_ON(!(read_cr0() & 8));
#endif

        /*
         * Reload esp0.
         * This is load_esp0(tss, next) with a multicall.
         */
        mcl->op      = __HYPERVISOR_stack_switch;
        mcl->args[0] = __KERNEL_DS;
        mcl->args[1] = next->esp0;
        mcl++;

        /*
         * Load the per-thread Thread-Local Storage descriptor.
         * This is load_TLS(next, cpu) with multicalls.
         */
#define C(i) do {                                                       \
        if (unlikely(next->tls_array[i].a != prev->tls_array[i].a ||    \
                     next->tls_array[i].b != prev->tls_array[i].b)) {   \
                mcl->op = __HYPERVISOR_update_descriptor;               \
                *(u64 *)&mcl->args[0] = virt_to_machine(                \
                        &get_cpu_gdt_table(cpu)[GDT_ENTRY_TLS_MIN + i]);\
                *(u64 *)&mcl->args[2] = *(u64 *)&next->tls_array[i];    \
                mcl++;                                                  \
        }                                                               \
} while (0)
        C(0); C(1); C(2);
#undef C

        if (unlikely(prev->iopl != next->iopl)) {
                iopl_op.iopl = (next->iopl == 0) ? 1 : (next->iopl >> 12) & 3;
                mcl->op      = __HYPERVISOR_physdev_op;
                mcl->args[0] = PHYSDEVOP_set_iopl;
                mcl->args[1] = (unsigned long)&iopl_op;
                mcl++;
        }

        if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) {
                set_xen_guest_handle(iobmp_op.bitmap,
                                     (char *)next->io_bitmap_ptr);
                iobmp_op.nr_ports = next->io_bitmap_ptr ? IO_BITMAP_BITS : 0;
                mcl->op      = __HYPERVISOR_physdev_op;
                mcl->args[0] = PHYSDEVOP_set_iobitmap;
                mcl->args[1] = (unsigned long)&iobmp_op;
                mcl++;
        }

        (void)HYPERVISOR_multicall(_mcl, mcl - _mcl);

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

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

        /*
         * Now maybe handle debug registers
         */
        if (unlikely(task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
                __switch_to_xtra(next_p);

        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;
}