x86: Simplify cpu_idle_wait

[safe/jmp/linux-2.6] / arch / x86 / kernel / process_32.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/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);

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);

                        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)
{
}

/*
 * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
 * pm_idle and update to new pm_idle value. Required while changing pm_idle
 * handler on SMP systems.
 *
 * Caller must have changed pm_idle to the new value before the call. Old
 * pm_idle value will not be used by any CPU after the return of this function.
 */
void cpu_idle_wait(void)
{
        smp_mb();
        /* kick all the CPUs so that they exit out of pm_idle */
        smp_call_function(do_nothing, NULL, 0, 1);
}
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;
}