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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/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 <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>

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.esp)[3];
}

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

void disable_hlt(void)
{
      hlt_counter++;
}

EXPORT_SYMBOL(disable_hlt);

void enable_hlt(void)
{
      hlt_counter--;
}

EXPORT_SYMBOL(enable_hlt);

/*
 * We use this if we don't have any better
 * idle routine..
 */
void default_idle(void)
{
      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())
                  safe_halt();      /* enables interrupts racelessly */
            else
                  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 (!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, 0, 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 eax, unsigned long ecx)
{
      if (!need_resched()) {
            __monitor((void *)&current_thread_info()->flags, 0, 0);
            smp_mb();
            if (!need_resched())
                  __mwait(eax, ecx);
      }
}

/* 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);
}

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

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

      if (user_mode_vm(regs)) {
            esp = regs->esp;
            ss = regs->xss & 0xffff;
            savesegment(gs, gs);
      } else {
            esp = (unsigned long) (&regs->esp);
            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->xcs, regs->eip, regs->eflags,
                  smp_processor_id());
      print_symbol("EIP is at %s\n", regs->eip);

      printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
            regs->eax, regs->ebx, regs->ecx, regs->edx);
      printk("ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
            regs->esi, regs->edi, regs->ebp, esp);
      printk(" DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
             regs->xds & 0xffff, regs->xes & 0xffff,
             regs->xfs & 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->esp);
}

/*
 * This gets run with %ebx containing the
 * function to call, and %edx 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.ebx = (unsigned long) fn;
      regs.edx = (unsigned long) arg;

      regs.xds = __USER_DS;
      regs.xes = __USER_DS;
      regs.xfs = __KERNEL_PERCPU;
      regs.orig_eax = -1;
      regs.eip = (unsigned long) kernel_thread_helper;
      regs.xcs = __KERNEL_CS | get_kernel_rpl();
      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;
            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;

      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(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);
      }

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

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

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

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

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

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

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

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

      dump->regs.ebx = regs->ebx;
      dump->regs.ecx = regs->ecx;
      dump->regs.edx = regs->edx;
      dump->regs.esi = regs->esi;
      dump->regs.edi = regs->edi;
      dump->regs.ebp = regs->ebp;
      dump->regs.eax = regs->eax;
      dump->regs.ds = regs->xds;
      dump->regs.es = regs->xes;
      dump->regs.fs = regs->xfs;
      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;
}

#ifdef CONFIG_SECCOMP
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();
}
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 *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);
      }

#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

      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 %eax) will be the "prev" task after
 * the task-switch, and shows up in ret_from_fork in entry.S,
 * for example.
 */
struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
{
      struct thread_struct *prev = &prev_p->thread,
                         *next = &next_p->thread;
      int cpu = smp_processor_id();
      struct tss_struct *tss = &per_cpu(init_tss, cpu);

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

      __unlazy_fpu(prev_p);


      /* 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_esp0(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.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 (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
            sp -= get_random_int() % 8192;
      return sp & ~0xf;
}

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