arch/x86/kernel/process_32.c - third_party/linux - Git at Google

 /*
  *  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/stddef.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/user.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 <linux/personality.h>
 #include <linux/tick.h>
 #include <linux/percpu.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>
 #include <asm/kdebug.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);

 DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
 EXPORT_PER_CPU_SYMBOL(current_task);

 DEFINE_PER_CPU(int, cpu_number);
 EXPORT_PER_CPU_SYMBOL(cpu_number);

 /*
  * Return saved PC of a blocked thread.
  */
 unsigned long thread_saved_pc(struct task_struct *tsk)
 {
 	return ((unsigned long *)tsk->thread.sp)[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)
 {
 	if (!hlt_counter && boot_cpu_data.hlt_works_ok) {
 		current_thread_info()->status &= ~TS_POLLING;
 		/*
 		 * TS_POLLING-cleared state must be visible before we
 		 * test NEED_RESCHED:
 		 */
 		smp_mb();

 		local_irq_disable();
 		if (!need_resched()) {
 			ktime_t t0, t1;
 			u64 t0n, t1n;

 			t0 = ktime_get();
 			t0n = ktime_to_ns(t0);
 			safe_halt();	/* enables interrupts racelessly */
 			local_irq_disable();
 			t1 = ktime_get();
 			t1n = ktime_to_ns(t1);
 			sched_clock_idle_wakeup_event(t1n - t0n);
 		}
 		local_irq_enable();
 		current_thread_info()->status |= TS_POLLING;
 	} else {
 		/* loop is done by the caller */
 		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)
 {
 	cpu_relax();
 }

 #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();

 	current_thread_info()->status |= TS_POLLING;

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

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

 			check_pgt_cache();
 			rmb();
 			idle = pm_idle;

 			if (rcu_pending(cpu))
 				rcu_check_callbacks(cpu, 0);

 			if (!idle)
 				idle = default_idle;

 			if (cpu_is_offline(cpu))
 				play_dead();

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

 static void do_nothing(void *unused)
 {
 }

 void cpu_idle_wait(void)
 {
 	unsigned int cpu, this_cpu = get_cpu();
 	cpumask_t map, tmp = current->cpus_allowed;

 	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);
 		/*
 		 * We waited 1 sec, if a CPU still did not call idle
 		 * it may be because it is in idle and not waking up
 		 * because it has nothing to do.
 		 * Give all the remaining CPUS a kick.
 		 */
 		smp_call_function_mask(map, do_nothing, NULL, 0);
 	} while (!cpus_empty(map));

 	set_cpus_allowed(current, tmp);
 }
 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).
  *
  * New with Core Duo processors, MWAIT can take some hints based on CPU
  * capability.
  */
 void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
 {
 	if (!need_resched()) {
 		__monitor((void *)&current_thread_info()->flags, 0, 0);
 		smp_mb();
 		if (!need_resched())
 			__mwait(ax, cx);
 	}
 }

 /* Default MONITOR/MWAIT with no hints, used for default C1 state */
 static void mwait_idle(void)
 {
 	local_irq_enable();
 	mwait_idle_with_hints(0, 0);
 }

 static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
 {
 	if (force_mwait)
 		return 1;
 	/* Any C1 states supported? */
 	return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
 }

 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 {
 	static int selected;

 	if (selected)
 		return;
 #ifdef CONFIG_X86_SMP
 	if (pm_idle == poll_idle && smp_num_siblings > 1) {
 		printk(KERN_WARNING "WARNING: polling idle and HT enabled,"
 			" performance may degrade.\n");
 	}
 #endif
 	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
 		/*
 		 * Skip, if setup has overridden idle.
 		 * One CPU supports mwait => All CPUs supports mwait
 		 */
 		if (!pm_idle) {
 			printk(KERN_INFO "using mwait in idle threads.\n");
 			pm_idle = mwait_idle;
 		}
 	}
 	selected = 1;
 }

 static int __init idle_setup(char *str)
 {
 	if (!strcmp(str, "poll")) {
 		printk("using polling idle threads.\n");
 		pm_idle = poll_idle;
 	} else if (!strcmp(str, "mwait"))
 		force_mwait = 1;
 	else
 		return -1;

 	boot_option_idle_override = 1;
 	return 0;
 }
 early_param("idle", idle_setup);

 void __show_registers(struct pt_regs *regs, int all)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 	unsigned long d0, d1, d2, d3, d6, d7;
 	unsigned long sp;
 	unsigned short ss, gs;

 	if (user_mode_vm(regs)) {
 		sp = regs->sp;
 		ss = regs->ss & 0xffff;
 		savesegment(gs, gs);
 	} else {
 		sp = (unsigned long) (&regs->sp);
 		savesegment(ss, ss);
 		savesegment(gs, gs);
 	}

 	printk("\n");
 	printk("Pid: %d, comm: %s %s (%s %.*s)\n",
 			task_pid_nr(current), current->comm,
 			print_tainted(), init_utsname()->release,
 			(int)strcspn(init_utsname()->version, " "),
 			init_utsname()->version);

 	printk("EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
 			0xffff & regs->cs, regs->ip, regs->flags,
 			smp_processor_id());
 	print_symbol("EIP is at %s\n", regs->ip);

 	printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
 		regs->ax, regs->bx, regs->cx, regs->dx);
 	printk("ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
 		regs->si, regs->di, regs->bp, sp);
 	printk(" DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
 	       regs->ds & 0xffff, regs->es & 0xffff,
 	       regs->fs & 0xffff, gs, ss);

 	if (!all)
 		return;

 	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);

 	get_debugreg(d0, 0);
 	get_debugreg(d1, 1);
 	get_debugreg(d2, 2);
 	get_debugreg(d3, 3);
 	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
 			d0, d1, d2, d3);

 	get_debugreg(d6, 6);
 	get_debugreg(d7, 7);
 	printk("DR6: %08lx DR7: %08lx\n",
 			d6, d7);
 }

 void show_regs(struct pt_regs *regs)
 {
 	__show_registers(regs, 1);
 	show_trace(NULL, regs, &regs->sp, regs->bp);
 }

 /*
  * This gets run with %bx containing the
  * function to call, and %dx containing
  * the "args".
  */
 extern void kernel_thread_helper(void);

 /*
  * 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.bx = (unsigned long) fn;
 	regs.dx = (unsigned long) arg;

 	regs.ds = __USER_DS;
 	regs.es = __USER_DS;
 	regs.fs = __KERNEL_PERCPU;
 	regs.orig_ax = -1;
 	regs.ip = (unsigned long) kernel_thread_helper;
 	regs.cs = __KERNEL_CS | get_kernel_rpl();
 	regs.flags = 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;
 		int cpu = get_cpu();
 		struct tss_struct *tss = &per_cpu(init_tss, cpu);

 		kfree(t->io_bitmap_ptr);
 		t->io_bitmap_ptr = NULL;
 		clear_thread_flag(TIF_IO_BITMAP);
 		/*
 		 * 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->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 		put_cpu();
 	}
 }

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

 	tsk->thread.debugreg0 = 0;
 	tsk->thread.debugreg1 = 0;
 	tsk->thread.debugreg2 = 0;
 	tsk->thread.debugreg3 = 0;
 	tsk->thread.debugreg6 = 0;
 	tsk->thread.debugreg7 = 0;
 	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 sp,
 	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->ax = 0;
 	childregs->sp = sp;

 	p->thread.sp = (unsigned long) childregs;
 	p->thread.sp0 = (unsigned long) (childregs+1);

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

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

 	tsk = current;
 	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
 		p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
 						IO_BITMAP_BYTES, GFP_KERNEL);
 		if (!p->thread.io_bitmap_ptr) {
 			p->thread.io_bitmap_max = 0;
 			return -ENOMEM;
 		}
 		set_tsk_thread_flag(p, TIF_IO_BITMAP);
 	}

 	err = 0;

 	/*
 	 * Set a new TLS for the child thread?
 	 */
 	if (clone_flags & CLONE_SETTLS)
 		err = do_set_thread_area(p, -1,
 			(struct user_desc __user *)childregs->si, 0);

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

 #ifdef CONFIG_SECCOMP
 static void hard_disable_TSC(void)
 {
 	write_cr4(read_cr4() | X86_CR4_TSD);
 }
 void disable_TSC(void)
 {
 	preempt_disable();
 	if (!test_and_set_thread_flag(TIF_NOTSC))
 		/*
 		 * Must flip the CPU state synchronously with
 		 * TIF_NOTSC in the current running context.
 		 */
 		hard_disable_TSC();
 	preempt_enable();
 }
 static void hard_enable_TSC(void)
 {
 	write_cr4(read_cr4() & ~X86_CR4_TSD);
 }
 #endif /* CONFIG_SECCOMP */

 static noinline void
 __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		 struct tss_struct *tss)
 {
 	struct thread_struct *prev, *next;
 	unsigned long debugctl;

 	prev = &prev_p->thread;
 	next = &next_p->thread;

 	debugctl = prev->debugctlmsr;
 	if (next->ds_area_msr != prev->ds_area_msr) {
 		/* we clear debugctl to make sure DS
 		 * is not in use when we change it */
 		debugctl = 0;
 		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
 		wrmsr(MSR_IA32_DS_AREA, next->ds_area_msr, 0);
 	}

 	if (next->debugctlmsr != debugctl)
 		wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);

 	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
 		set_debugreg(next->debugreg0, 0);
 		set_debugreg(next->debugreg1, 1);
 		set_debugreg(next->debugreg2, 2);
 		set_debugreg(next->debugreg3, 3);
 		/* no 4 and 5 */
 		set_debugreg(next->debugreg6, 6);
 		set_debugreg(next->debugreg7, 7);
 	}

 #ifdef CONFIG_SECCOMP
 	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
 	    test_tsk_thread_flag(next_p, TIF_NOTSC)) {
 		/* prev and next are different */
 		if (test_tsk_thread_flag(next_p, TIF_NOTSC))
 			hard_disable_TSC();
 		else
 			hard_enable_TSC();
 	}
 #endif

 #ifdef X86_BTS
 	if (test_tsk_thread_flag(prev_p, TIF_BTS_TRACE_TS))
 		ptrace_bts_take_timestamp(prev_p, BTS_TASK_DEPARTS);

 	if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
 		ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
 #endif


 	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
 		/*
 		 * Disable the bitmap via an invalid offset. We still cache
 		 * the previous bitmap owner and the IO bitmap contents:
 		 */
 		tss->x86_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->x86_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->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 }

 /*
  *	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 %ax) will be the "prev" task after
  * the task-switch, and shows up in ret_from_fork in entry.S,
  * for example.
  */
 struct task_struct * __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);


 	/* we're going to use this soon, after a few expensive things */
 	if (next_p->fpu_counter > 5)
 		prefetch(&next->i387.fxsave);

 	/*
 	 * Reload esp0.
 	 */
 	load_sp0(tss, next);

 	/*
 	 * Save away %gs. No need to save %fs, as it was saved on the
 	 * stack on entry.  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(gs, prev->gs);

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

 	/*
 	 * Restore IOPL if needed.  In normal use, the flags restore
 	 * in the switch assembly will handle this.  But if the kernel
 	 * is running virtualized at a non-zero CPL, the popf will
 	 * not restore flags, so it must be done in a separate step.
 	 */
 	if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
 		set_iopl_mask(next->iopl);

 	/*
 	 * Now maybe handle debug registers and/or IO bitmaps
 	 */
 	if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
 		     task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
 		__switch_to_xtra(prev_p, next_p, tss);

 	/*
 	 * Leave lazy mode, flushing any hypercalls made here.
 	 * This must be done before restoring TLS segments so
 	 * the GDT and LDT are properly updated, and must be
 	 * done before math_state_restore, so the TS bit is up
 	 * to date.
 	 */
 	arch_leave_lazy_cpu_mode();

 	/* If the task has used fpu the last 5 timeslices, just do a full
 	 * restore of the math state immediately to avoid the trap; the
 	 * chances of needing FPU soon are obviously high now
 	 */
 	if (next_p->fpu_counter > 5)
 		math_state_restore();

 	/*
 	 * Restore %gs if needed (which is common)
 	 */
 	if (prev->gs | next->gs)
 		loadsegment(gs, next->gs);

 	x86_write_percpu(current_task, next_p);

 	return prev_p;
 }

 asmlinkage int sys_fork(struct pt_regs regs)
 {
 	return do_fork(SIGCHLD, regs.sp, &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.bx;
 	newsp = regs.cx;
 	parent_tidptr = (int __user *)regs.dx;
 	child_tidptr = (int __user *)regs.di;
 	if (!newsp)
 		newsp = regs.sp;
 	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.sp, &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.bx);
 	error = PTR_ERR(filename);
 	if (IS_ERR(filename))
 		goto out;
 	error = do_execve(filename,
 			(char __user * __user *) regs.cx,
 			(char __user * __user *) regs.dx,
 			&regs);
 	if (error == 0) {
 		/* 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 bp, sp, ip;
 	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);
 	sp = p->thread.sp;
 	if (!stack_page || sp < stack_page || sp > top_esp+stack_page)
 		return 0;
 	/* include/asm-i386/system.h:switch_to() pushes bp last. */
 	bp = *(unsigned long *) sp;
 	do {
 		if (bp < stack_page || bp > top_ebp+stack_page)
 			return 0;
 		ip = *(unsigned long *) (bp+4);
 		if (!in_sched_functions(ip))
 			return ip;
 		bp = *(unsigned long *) bp;
 	} while (count++ < 16);
 	return 0;
 }

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

 unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
 	unsigned long range_end = mm->brk + 0x02000000;
 	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
 }
	/*
	* 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/stddef.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/user.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 <linux/personality.h>
	#include <linux/tick.h>
	#include <linux/percpu.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>
	#include <asm/kdebug.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);

	DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
	EXPORT_PER_CPU_SYMBOL(current_task);

	DEFINE_PER_CPU(int, cpu_number);
	EXPORT_PER_CPU_SYMBOL(cpu_number);

	/*
	* Return saved PC of a blocked thread.
	*/
	unsigned long thread_saved_pc(struct task_struct *tsk)
	{
	return ((unsigned long *)tsk->thread.sp)[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)
	{
	if (!hlt_counter && boot_cpu_data.hlt_works_ok) {
	current_thread_info()->status &= ~TS_POLLING;
	/*
	* TS_POLLING-cleared state must be visible before we
	* test NEED_RESCHED:
	*/
	smp_mb();

	local_irq_disable();
	if (!need_resched()) {
	ktime_t t0, t1;
	u64 t0n, t1n;

	t0 = ktime_get();
	t0n = ktime_to_ns(t0);
	safe_halt(); /* enables interrupts racelessly */
	local_irq_disable();
	t1 = ktime_get();
	t1n = ktime_to_ns(t1);
	sched_clock_idle_wakeup_event(t1n - t0n);
	}
	local_irq_enable();
	current_thread_info()->status \|= TS_POLLING;
	} else {
	/* loop is done by the caller */
	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)
	{
	cpu_relax();
	}

	#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();

	current_thread_info()->status \|= TS_POLLING;

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

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

	check_pgt_cache();
	rmb();
	idle = pm_idle;

	if (rcu_pending(cpu))
	rcu_check_callbacks(cpu, 0);

	if (!idle)
	idle = default_idle;

	if (cpu_is_offline(cpu))
	play_dead();

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

	static void do_nothing(void *unused)
	{
	}

	void cpu_idle_wait(void)
	{
	unsigned int cpu, this_cpu = get_cpu();
	cpumask_t map, tmp = current->cpus_allowed;

	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);
	/*
	* We waited 1 sec, if a CPU still did not call idle
	* it may be because it is in idle and not waking up
	* because it has nothing to do.
	* Give all the remaining CPUS a kick.
	*/
	smp_call_function_mask(map, do_nothing, NULL, 0);
	} while (!cpus_empty(map));

	set_cpus_allowed(current, tmp);
	}
	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).
	*
	* New with Core Duo processors, MWAIT can take some hints based on CPU
	* capability.
	*/
	void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
	{
	if (!need_resched()) {
	__monitor((void *)&current_thread_info()->flags, 0, 0);
	smp_mb();
	if (!need_resched())
	__mwait(ax, cx);
	}
	}

	/* Default MONITOR/MWAIT with no hints, used for default C1 state */
	static void mwait_idle(void)
	{
	local_irq_enable();
	mwait_idle_with_hints(0, 0);
	}

	static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
	{
	if (force_mwait)
	return 1;
	/* Any C1 states supported? */
	return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
	}

	void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
	{
	static int selected;

	if (selected)
	return;
	#ifdef CONFIG_X86_SMP
	if (pm_idle == poll_idle && smp_num_siblings > 1) {
	printk(KERN_WARNING "WARNING: polling idle and HT enabled,"
	" performance may degrade.\n");
	}
	#endif
	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
	/*
	* Skip, if setup has overridden idle.
	* One CPU supports mwait => All CPUs supports mwait
	*/
	if (!pm_idle) {
	printk(KERN_INFO "using mwait in idle threads.\n");
	pm_idle = mwait_idle;
	}
	}
	selected = 1;
	}

	static int __init idle_setup(char *str)
	{
	if (!strcmp(str, "poll")) {
	printk("using polling idle threads.\n");
	pm_idle = poll_idle;
	} else if (!strcmp(str, "mwait"))
	force_mwait = 1;
	else
	return -1;

	boot_option_idle_override = 1;
	return 0;
	}
	early_param("idle", idle_setup);

	void __show_registers(struct pt_regs *regs, int all)
	{
	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
	unsigned long d0, d1, d2, d3, d6, d7;
	unsigned long sp;
	unsigned short ss, gs;

	if (user_mode_vm(regs)) {
	sp = regs->sp;
	ss = regs->ss & 0xffff;
	savesegment(gs, gs);
	} else {
	sp = (unsigned long) (&regs->sp);
	savesegment(ss, ss);
	savesegment(gs, gs);
	}

	printk("\n");
	printk("Pid: %d, comm: %s %s (%s %.*s)\n",
	task_pid_nr(current), current->comm,
	print_tainted(), init_utsname()->release,
	(int)strcspn(init_utsname()->version, " "),
	init_utsname()->version);

	printk("EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
	0xffff & regs->cs, regs->ip, regs->flags,
	smp_processor_id());
	print_symbol("EIP is at %s\n", regs->ip);

	printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
	regs->ax, regs->bx, regs->cx, regs->dx);
	printk("ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
	regs->si, regs->di, regs->bp, sp);
	printk(" DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
	regs->ds & 0xffff, regs->es & 0xffff,
	regs->fs & 0xffff, gs, ss);

	if (!all)
	return;

	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);

	get_debugreg(d0, 0);
	get_debugreg(d1, 1);
	get_debugreg(d2, 2);
	get_debugreg(d3, 3);
	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
	d0, d1, d2, d3);

	get_debugreg(d6, 6);
	get_debugreg(d7, 7);
	printk("DR6: %08lx DR7: %08lx\n",
	d6, d7);
	}

	void show_regs(struct pt_regs *regs)
	{
	__show_registers(regs, 1);
	show_trace(NULL, regs, &regs->sp, regs->bp);
	}

	/*
	* This gets run with %bx containing the
	* function to call, and %dx containing
	* the "args".
	*/
	extern void kernel_thread_helper(void);

	/*
	* 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.bx = (unsigned long) fn;
	regs.dx = (unsigned long) arg;

	regs.ds = __USER_DS;
	regs.es = __USER_DS;
	regs.fs = __KERNEL_PERCPU;
	regs.orig_ax = -1;
	regs.ip = (unsigned long) kernel_thread_helper;
	regs.cs = __KERNEL_CS \| get_kernel_rpl();
	regs.flags = 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;
	int cpu = get_cpu();
	struct tss_struct *tss = &per_cpu(init_tss, cpu);

	kfree(t->io_bitmap_ptr);
	t->io_bitmap_ptr = NULL;
	clear_thread_flag(TIF_IO_BITMAP);
	/*
	* 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->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
	put_cpu();
	}
	}

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

	tsk->thread.debugreg0 = 0;
	tsk->thread.debugreg1 = 0;
	tsk->thread.debugreg2 = 0;
	tsk->thread.debugreg3 = 0;
	tsk->thread.debugreg6 = 0;
	tsk->thread.debugreg7 = 0;
	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 sp,
	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->ax = 0;
	childregs->sp = sp;

	p->thread.sp = (unsigned long) childregs;
	p->thread.sp0 = (unsigned long) (childregs+1);

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

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

	tsk = current;
	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
	p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
	IO_BITMAP_BYTES, GFP_KERNEL);
	if (!p->thread.io_bitmap_ptr) {
	p->thread.io_bitmap_max = 0;
	return -ENOMEM;
	}
	set_tsk_thread_flag(p, TIF_IO_BITMAP);
	}

	err = 0;

	/*
	* Set a new TLS for the child thread?
	*/
	if (clone_flags & CLONE_SETTLS)
	err = do_set_thread_area(p, -1,
	(struct user_desc __user *)childregs->si, 0);

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

	#ifdef CONFIG_SECCOMP
	static void hard_disable_TSC(void)
	{
	write_cr4(read_cr4() \| X86_CR4_TSD);
	}
	void disable_TSC(void)
	{
	preempt_disable();
	if (!test_and_set_thread_flag(TIF_NOTSC))
	/*
	* Must flip the CPU state synchronously with
	* TIF_NOTSC in the current running context.
	*/
	hard_disable_TSC();
	preempt_enable();
	}
	static void hard_enable_TSC(void)
	{
	write_cr4(read_cr4() & ~X86_CR4_TSD);
	}
	#endif /* CONFIG_SECCOMP */

	static noinline void
	__switch_to_xtra(struct task_struct prev_p, struct task_struct next_p,
	struct tss_struct *tss)
	{
	struct thread_struct prev, next;
	unsigned long debugctl;

	prev = &prev_p->thread;
	next = &next_p->thread;

	debugctl = prev->debugctlmsr;
	if (next->ds_area_msr != prev->ds_area_msr) {
	/* we clear debugctl to make sure DS
	* is not in use when we change it */
	debugctl = 0;
	wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
	wrmsr(MSR_IA32_DS_AREA, next->ds_area_msr, 0);
	}

	if (next->debugctlmsr != debugctl)
	wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);

	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
	set_debugreg(next->debugreg0, 0);
	set_debugreg(next->debugreg1, 1);
	set_debugreg(next->debugreg2, 2);
	set_debugreg(next->debugreg3, 3);
	/* no 4 and 5 */
	set_debugreg(next->debugreg6, 6);
	set_debugreg(next->debugreg7, 7);
	}

	#ifdef CONFIG_SECCOMP
	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
	test_tsk_thread_flag(next_p, TIF_NOTSC)) {
	/* prev and next are different */
	if (test_tsk_thread_flag(next_p, TIF_NOTSC))
	hard_disable_TSC();
	else
	hard_enable_TSC();
	}
	#endif

	#ifdef X86_BTS
	if (test_tsk_thread_flag(prev_p, TIF_BTS_TRACE_TS))
	ptrace_bts_take_timestamp(prev_p, BTS_TASK_DEPARTS);

	if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
	ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
	#endif


	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
	/*
	* Disable the bitmap via an invalid offset. We still cache
	* the previous bitmap owner and the IO bitmap contents:
	*/
	tss->x86_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->x86_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->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
	}

	/*
	* 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 %ax) will be the "prev" task after
	* the task-switch, and shows up in ret_from_fork in entry.S,
	* for example.
	*/
	struct task_struct * __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);


	/* we're going to use this soon, after a few expensive things */
	if (next_p->fpu_counter > 5)
	prefetch(&next->i387.fxsave);

	/*
	* Reload esp0.
	*/
	load_sp0(tss, next);

	/*
	* Save away %gs. No need to save %fs, as it was saved on the
	* stack on entry. 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(gs, prev->gs);

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

	/*
	* Restore IOPL if needed. In normal use, the flags restore
	* in the switch assembly will handle this. But if the kernel
	* is running virtualized at a non-zero CPL, the popf will
	* not restore flags, so it must be done in a separate step.
	*/
	if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
	set_iopl_mask(next->iopl);

	/*
	* Now maybe handle debug registers and/or IO bitmaps
	*/
	if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV \|\|
	task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
	__switch_to_xtra(prev_p, next_p, tss);

	/*
	* Leave lazy mode, flushing any hypercalls made here.
	* This must be done before restoring TLS segments so
	* the GDT and LDT are properly updated, and must be
	* done before math_state_restore, so the TS bit is up
	* to date.
	*/
	arch_leave_lazy_cpu_mode();

	/* If the task has used fpu the last 5 timeslices, just do a full
	* restore of the math state immediately to avoid the trap; the
	* chances of needing FPU soon are obviously high now
	*/
	if (next_p->fpu_counter > 5)
	math_state_restore();

	/*
	* Restore %gs if needed (which is common)
	*/
	if (prev->gs \| next->gs)
	loadsegment(gs, next->gs);

	x86_write_percpu(current_task, next_p);

	return prev_p;
	}

	asmlinkage int sys_fork(struct pt_regs regs)
	{
	return do_fork(SIGCHLD, regs.sp, &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.bx;
	newsp = regs.cx;
	parent_tidptr = (int __user *)regs.dx;
	child_tidptr = (int __user *)regs.di;
	if (!newsp)
	newsp = regs.sp;
	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.sp, &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.bx);
	error = PTR_ERR(filename);
	if (IS_ERR(filename))
	goto out;
	error = do_execve(filename,
	(char __user * __user *) regs.cx,
	(char __user * __user *) regs.dx,
	&regs);
	if (error == 0) {
	/* 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 bp, sp, ip;
	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);
	sp = p->thread.sp;
	if (!stack_page \|\| sp < stack_page \|\| sp > top_esp+stack_page)
	return 0;
	/* include/asm-i386/system.h:switch_to() pushes bp last. */
	bp = (unsigned long ) sp;
	do {
	if (bp < stack_page \|\| bp > top_ebp+stack_page)
	return 0;
	ip = (unsigned long ) (bp+4);
	if (!in_sched_functions(ip))
	return ip;
	bp = (unsigned long ) bp;
	} while (count++ < 16);
	return 0;
	}

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

	unsigned long arch_randomize_brk(struct mm_struct *mm)
	{
	unsigned long range_end = mm->brk + 0x02000000;
	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
	}