arch/i386/kernel/process.c

   1 /*
   2  *  linux/arch/i386/kernel/process.c
   3  *
   4  *  Copyright (C) 1995  Linus Torvalds
   5  *
   6  *  Pentium III FXSR, SSE support
   7  *      Gareth Hughes <gareth@valinux.com>, May 2000
   8  */
   9
  10 /*
  11  * This file handles the architecture-dependent parts of process handling..
  12  */
  13
  14 #include <stdarg.h>
  15
  16 #include <linux/cpu.h>
  17 #include <linux/errno.h>
  18 #include <linux/sched.h>
  19 #include <linux/fs.h>
  20 #include <linux/kernel.h>
  21 #include <linux/mm.h>
  22 #include <linux/elfcore.h>
  23 #include <linux/smp.h>
  24 #include <linux/smp_lock.h>
  25 #include <linux/stddef.h>
  26 #include <linux/slab.h>
  27 #include <linux/vmalloc.h>
  28 #include <linux/user.h>
  29 #include <linux/a.out.h>
  30 #include <linux/interrupt.h>
  31 #include <linux/config.h>
  32 #include <linux/utsname.h>
  33 #include <linux/delay.h>
  34 #include <linux/reboot.h>
  35 #include <linux/init.h>
  36 #include <linux/mc146818rtc.h>
  37 #include <linux/module.h>
  38 #include <linux/kallsyms.h>
  39 #include <linux/ptrace.h>
  40 #include <linux/random.h>
  41 #include <linux/kprobes.h>
  42
  43 #include <asm/uaccess.h>
  44 #include <asm/pgtable.h>
  45 #include <asm/system.h>
  46 #include <asm/io.h>
  47 #include <asm/ldt.h>
  48 #include <asm/processor.h>
  49 #include <asm/i387.h>
  50 #include <asm/desc.h>
  51 #include <asm/vm86.h>
  52 #ifdef CONFIG_MATH_EMULATION
  53 #include <asm/math_emu.h>
  54 #endif
  55
  56 #include <linux/err.h>
  57
  58 #include <asm/tlbflush.h>
  59 #include <asm/cpu.h>
  60
  61 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
  62
  63 static int hlt_counter;
  64
  65 unsigned long boot_option_idle_override = 0;
  66 EXPORT_SYMBOL(boot_option_idle_override);
  67
  68 /*
  69  * Return saved PC of a blocked thread.
  70  */
  71 unsigned long thread_saved_pc(struct task_struct *tsk)
  72 {
  73         return ((unsigned long *)tsk->thread.esp)[3];
  74 }
  75
  76 /*
  77  * Powermanagement idle function, if any..
  78  */
  79 void (*pm_idle)(void);
  80 EXPORT_SYMBOL(pm_idle);
  81 static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
  82
  83 void disable_hlt(void)
  84 {
  85         hlt_counter++;
  86 }
  87
  88 EXPORT_SYMBOL(disable_hlt);
  89
  90 void enable_hlt(void)
  91 {
  92         hlt_counter--;
  93 }
  94
  95 EXPORT_SYMBOL(enable_hlt);
  96
  97 /*
  98  * We use this if we don't have any better
  99  * idle routine..
 100  */
 101 void default_idle(void)
 102 {
 103         local_irq_enable();
 104
 105         if (!hlt_counter && boot_cpu_data.hlt_works_ok) {
 106                 clear_thread_flag(TIF_POLLING_NRFLAG);
 107                 smp_mb__after_clear_bit();
 108                 while (!need_resched()) {
 109                         local_irq_disable();
 110                         if (!need_resched())
 111                                 safe_halt();
 112                         else
 113                                 local_irq_enable();
 114                 }
 115                 set_thread_flag(TIF_POLLING_NRFLAG);
 116         } else {
 117                 while (!need_resched())
 118                         cpu_relax();
 119         }
 120 }
 121 #ifdef CONFIG_APM_MODULE
 122 EXPORT_SYMBOL(default_idle);
 123 #endif
 124
 125 /*
 126  * On SMP it's slightly faster (but much more power-consuming!)
 127  * to poll the ->work.need_resched flag instead of waiting for the
 128  * cross-CPU IPI to arrive. Use this option with caution.
 129  */
 130 static void poll_idle (void)
 131 {
 132         local_irq_enable();
 133
 134         asm volatile(
 135                 "2:"
 136                 "testl %0, %1;"
 137                 "rep; nop;"
 138                 "je 2b;"
 139                 : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags));
 140 }
 141
 142 #ifdef CONFIG_HOTPLUG_CPU
 143 #include <asm/nmi.h>
 144 /* We don't actually take CPU down, just spin without interrupts. */
 145 static inline void play_dead(void)
 146 {
 147         /* This must be done before dead CPU ack */
 148         cpu_exit_clear();
 149         wbinvd();
 150         mb();
 151         /* Ack it */
 152         __get_cpu_var(cpu_state) = CPU_DEAD;
 153
 154         /*
 155          * With physical CPU hotplug, we should halt the cpu
 156          */
 157         local_irq_disable();
 158         while (1)
 159                 halt();
 160 }
 161 #else
 162 static inline void play_dead(void)
 163 {
 164         BUG();
 165 }
 166 #endif /* CONFIG_HOTPLUG_CPU */
 167
 168 /*
 169  * The idle thread. There's no useful work to be
 170  * done, so just try to conserve power and have a
 171  * low exit latency (ie sit in a loop waiting for
 172  * somebody to say that they'd like to reschedule)
 173  */
 174 void cpu_idle(void)
 175 {
 176         int cpu = smp_processor_id();
 177
 178         set_thread_flag(TIF_POLLING_NRFLAG);
 179
 180         /* endless idle loop with no priority at all */
 181         while (1) {
 182                 while (!need_resched()) {
 183                         void (*idle)(void);
 184
 185                         if (__get_cpu_var(cpu_idle_state))
 186                                 __get_cpu_var(cpu_idle_state) = 0;
 187
 188                         rmb();
 189                         idle = pm_idle;
 190
 191                         if (!idle)
 192                                 idle = default_idle;
 193
 194                         if (cpu_is_offline(cpu))
 195                                 play_dead();
 196
 197                         __get_cpu_var(irq_stat).idle_timestamp = jiffies;
 198                         idle();
 199                 }
 200                 preempt_enable_no_resched();
 201                 schedule();
 202                 preempt_disable();
 203         }
 204 }
 205
 206 void cpu_idle_wait(void)
 207 {
 208         unsigned int cpu, this_cpu = get_cpu();
 209         cpumask_t map;
 210
 211         set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
 212         put_cpu();
 213
 214         cpus_clear(map);
 215         for_each_online_cpu(cpu) {
 216                 per_cpu(cpu_idle_state, cpu) = 1;
 217                 cpu_set(cpu, map);
 218         }
 219
 220         __get_cpu_var(cpu_idle_state) = 0;
 221
 222         wmb();
 223         do {
 224                 ssleep(1);
 225                 for_each_online_cpu(cpu) {
 226                         if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
 227                                 cpu_clear(cpu, map);
 228                 }
 229                 cpus_and(map, map, cpu_online_map);
 230         } while (!cpus_empty(map));
 231 }
 232 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 233
 234 /*
 235  * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
 236  * which can obviate IPI to trigger checking of need_resched.
 237  * We execute MONITOR against need_resched and enter optimized wait state
 238  * through MWAIT. Whenever someone changes need_resched, we would be woken
 239  * up from MWAIT (without an IPI).
 240  */
 241 static void mwait_idle(void)
 242 {
 243         local_irq_enable();
 244
 245         while (!need_resched()) {
 246                 __monitor((void *)&current_thread_info()->flags, 0, 0);
 247                 smp_mb();
 248                 if (need_resched())
 249                         break;
 250                 __mwait(0, 0);
 251         }
 252 }
 253
 254 void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
 255 {
 256         if (cpu_has(c, X86_FEATURE_MWAIT)) {
 257                 printk("monitor/mwait feature present.\n");
 258                 /*
 259                  * Skip, if setup has overridden idle.
 260                  * One CPU supports mwait => All CPUs supports mwait
 261                  */
 262                 if (!pm_idle) {
 263                         printk("using mwait in idle threads.\n");
 264                         pm_idle = mwait_idle;
 265                 }
 266         }
 267 }
 268
 269 static int __init idle_setup (char *str)
 270 {
 271         if (!strncmp(str, "poll", 4)) {
 272                 printk("using polling idle threads.\n");
 273                 pm_idle = poll_idle;
 274 #ifdef CONFIG_X86_SMP
 275                 if (smp_num_siblings > 1)
 276                         printk("WARNING: polling idle and HT enabled, performance may degrade.\n");
 277 #endif
 278         } else if (!strncmp(str, "halt", 4)) {
 279                 printk("using halt in idle threads.\n");
 280                 pm_idle = default_idle;
 281         }
 282
 283         boot_option_idle_override = 1;
 284         return 1;
 285 }
 286
 287 __setup("idle=", idle_setup);
 288
 289 void show_regs(struct pt_regs * regs)
 290 {
 291         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 292
 293         printk("\n");
 294         printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
 295         printk("EIP: %04x:[<%08lx>] CPU: %d\n",0xffff & regs->xcs,regs->eip, smp_processor_id());
 296         print_symbol("EIP is at %s\n", regs->eip);
 297
 298         if (user_mode(regs))
 299                 printk(" ESP: %04x:%08lx",0xffff & regs->xss,regs->esp);
 300         printk(" EFLAGS: %08lx    %s  (%s)\n",
 301                regs->eflags, print_tainted(), system_utsname.release);
 302         printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
 303                 regs->eax,regs->ebx,regs->ecx,regs->edx);
 304         printk("ESI: %08lx EDI: %08lx EBP: %08lx",
 305                 regs->esi, regs->edi, regs->ebp);
 306         printk(" DS: %04x ES: %04x\n",
 307                 0xffff & regs->xds,0xffff & regs->xes);
 308
 309         cr0 = read_cr0();
 310         cr2 = read_cr2();
 311         cr3 = read_cr3();
 312         cr4 = read_cr4_safe();
 313         printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n", cr0, cr2, cr3, cr4);
 314         show_trace(NULL, &regs->esp);
 315 }
 316
 317 /*
 318  * This gets run with %ebx containing the
 319  * function to call, and %edx containing
 320  * the "args".
 321  */
 322 extern void kernel_thread_helper(void);
 323 __asm__(".section .text\n"
 324         ".align 4\n"
 325         "kernel_thread_helper:\n\t"
 326         "movl %edx,%eax\n\t"
 327         "pushl %edx\n\t"
 328         "call *%ebx\n\t"
 329         "pushl %eax\n\t"
 330         "call do_exit\n"
 331         ".previous");
 332
 333 /*
 334  * Create a kernel thread
 335  */
 336 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 337 {
 338         struct pt_regs regs;
 339
 340         memset(&regs, 0, sizeof(regs));
 341
 342         regs.ebx = (unsigned long) fn;
 343         regs.edx = (unsigned long) arg;
 344
 345         regs.xds = __USER_DS;
 346         regs.xes = __USER_DS;
 347         regs.orig_eax = -1;
 348         regs.eip = (unsigned long) kernel_thread_helper;
 349         regs.xcs = __KERNEL_CS;
 350         regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
 351
 352         /* Ok, create the new process.. */
 353         return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
 354 }
 355 EXPORT_SYMBOL(kernel_thread);
 356
 357 /*
 358  * Free current thread data structures etc..
 359  */
 360 void exit_thread(void)
 361 {
 362         struct task_struct *tsk = current;
 363         struct thread_struct *t = &tsk->thread;
 364
 365         /*
 366          * Remove function-return probe instances associated with this task
 367          * and put them back on the free list. Do not insert an exit probe for
 368          * this function, it will be disabled by kprobe_flush_task if you do.
 369          */
 370         kprobe_flush_task(tsk);
 371
 372         /* The process may have allocated an io port bitmap... nuke it. */
 373         if (unlikely(NULL != t->io_bitmap_ptr)) {
 374                 int cpu = get_cpu();
 375                 struct tss_struct *tss = &per_cpu(init_tss, cpu);
 376
 377                 kfree(t->io_bitmap_ptr);
 378                 t->io_bitmap_ptr = NULL;
 379                 /*
 380                  * Careful, clear this in the TSS too:
 381                  */
 382                 memset(tss->io_bitmap, 0xff, tss->io_bitmap_max);
 383                 t->io_bitmap_max = 0;
 384                 tss->io_bitmap_owner = NULL;
 385                 tss->io_bitmap_max = 0;
 386                 tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 387                 put_cpu();
 388         }
 389 }
 390
 391 void flush_thread(void)
 392 {
 393         struct task_struct *tsk = current;
 394
 395         memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
 396         memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
 397         /*
 398          * Forget coprocessor state..
 399          */
 400         clear_fpu(tsk);
 401         clear_used_math();
 402 }
 403
 404 void release_thread(struct task_struct *dead_task)
 405 {
 406         BUG_ON(dead_task->mm);
 407         release_vm86_irqs(dead_task);
 408 }
 409
 410 /*
 411  * This gets called before we allocate a new thread and copy
 412  * the current task into it.
 413  */
 414 void prepare_to_copy(struct task_struct *tsk)
 415 {
 416         unlazy_fpu(tsk);
 417 }
 418
 419 int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
 420         unsigned long unused,
 421         struct task_struct * p, struct pt_regs * regs)
 422 {
 423         struct pt_regs * childregs;
 424         struct task_struct *tsk;
 425         int err;
 426
 427         childregs = task_pt_regs(p);
 428         *childregs = *regs;
 429         childregs->eax = 0;
 430         childregs->esp = esp;
 431
 432         p->thread.esp = (unsigned long) childregs;
 433         p->thread.esp0 = (unsigned long) (childregs+1);
 434
 435         p->thread.eip = (unsigned long) ret_from_fork;
 436
 437         savesegment(fs,p->thread.fs);
 438         savesegment(gs,p->thread.gs);
 439
 440         tsk = current;
 441         if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
 442                 p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
 443                 if (!p->thread.io_bitmap_ptr) {
 444                         p->thread.io_bitmap_max = 0;
 445                         return -ENOMEM;
 446                 }
 447                 memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
 448                         IO_BITMAP_BYTES);
 449         }
 450
 451         /*
 452          * Set a new TLS for the child thread?
 453          */
 454         if (clone_flags & CLONE_SETTLS) {
 455                 struct desc_struct *desc;
 456                 struct user_desc info;
 457                 int idx;
 458
 459                 err = -EFAULT;
 460                 if (copy_from_user(&info, (void __user *)childregs->esi, sizeof(info)))
 461                         goto out;
 462                 err = -EINVAL;
 463                 if (LDT_empty(&info))
 464                         goto out;
 465
 466                 idx = info.entry_number;
 467                 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 468                         goto out;
 469
 470                 desc = p->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
 471                 desc->a = LDT_entry_a(&info);
 472                 desc->b = LDT_entry_b(&info);
 473         }
 474
 475         err = 0;
 476  out:
 477         if (err && p->thread.io_bitmap_ptr) {
 478                 kfree(p->thread.io_bitmap_ptr);
 479                 p->thread.io_bitmap_max = 0;
 480         }
 481         return err;
 482 }
 483
 484 /*
 485  * fill in the user structure for a core dump..
 486  */
 487 void dump_thread(struct pt_regs * regs, struct user * dump)
 488 {
 489         int i;
 490
 491 /* changed the size calculations - should hopefully work better. lbt */
 492         dump->magic = CMAGIC;
 493         dump->start_code = 0;
 494         dump->start_stack = regs->esp & ~(PAGE_SIZE - 1);
 495         dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
 496         dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
 497         dump->u_dsize -= dump->u_tsize;
 498         dump->u_ssize = 0;
 499         for (i = 0; i < 8; i++)
 500                 dump->u_debugreg[i] = current->thread.debugreg[i];
 501
 502         if (dump->start_stack < TASK_SIZE)
 503                 dump->u_ssize = ((unsigned long) (TASK_SIZE - dump->start_stack)) >> PAGE_SHIFT;
 504
 505         dump->regs.ebx = regs->ebx;
 506         dump->regs.ecx = regs->ecx;
 507         dump->regs.edx = regs->edx;
 508         dump->regs.esi = regs->esi;
 509         dump->regs.edi = regs->edi;
 510         dump->regs.ebp = regs->ebp;
 511         dump->regs.eax = regs->eax;
 512         dump->regs.ds = regs->xds;
 513         dump->regs.es = regs->xes;
 514         savesegment(fs,dump->regs.fs);
 515         savesegment(gs,dump->regs.gs);
 516         dump->regs.orig_eax = regs->orig_eax;
 517         dump->regs.eip = regs->eip;
 518         dump->regs.cs = regs->xcs;
 519         dump->regs.eflags = regs->eflags;
 520         dump->regs.esp = regs->esp;
 521         dump->regs.ss = regs->xss;
 522
 523         dump->u_fpvalid = dump_fpu (regs, &dump->i387);
 524 }
 525 EXPORT_SYMBOL(dump_thread);
 526
 527 /*
 528  * Capture the user space registers if the task is not running (in user space)
 529  */
 530 int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
 531 {
 532         struct pt_regs ptregs = *task_pt_regs(tsk);
 533         ptregs.xcs &= 0xffff;
 534         ptregs.xds &= 0xffff;
 535         ptregs.xes &= 0xffff;
 536         ptregs.xss &= 0xffff;
 537
 538         elf_core_copy_regs(regs, &ptregs);
 539
 540         return 1;
 541 }
 542
 543 static inline void
 544 handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
 545 {
 546         if (!next->io_bitmap_ptr) {
 547                 /*
 548                  * Disable the bitmap via an invalid offset. We still cache
 549                  * the previous bitmap owner and the IO bitmap contents:
 550                  */
 551                 tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 552                 return;
 553         }
 554         if (likely(next == tss->io_bitmap_owner)) {
 555                 /*
 556                  * Previous owner of the bitmap (hence the bitmap content)
 557                  * matches the next task, we dont have to do anything but
 558                  * to set a valid offset in the TSS:
 559                  */
 560                 tss->io_bitmap_base = IO_BITMAP_OFFSET;
 561                 return;
 562         }
 563         /*
 564          * Lazy TSS's I/O bitmap copy. We set an invalid offset here
 565          * and we let the task to get a GPF in case an I/O instruction
 566          * is performed.  The handler of the GPF will verify that the
 567          * faulting task has a valid I/O bitmap and, it true, does the
 568          * real copy and restart the instruction.  This will save us
 569          * redundant copies when the currently switched task does not
 570          * perform any I/O during its timeslice.
 571          */
 572         tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 573 }
 574
 575 /*
 576  * This function selects if the context switch from prev to next
 577  * has to tweak the TSC disable bit in the cr4.
 578  */
 579 static inline void disable_tsc(struct task_struct *prev_p,
 580                                struct task_struct *next_p)
 581 {
 582         struct thread_info *prev, *next;
 583
 584         /*
 585          * gcc should eliminate the ->thread_info dereference if
 586          * has_secure_computing returns 0 at compile time (SECCOMP=n).
 587          */
 588         prev = task_thread_info(prev_p);
 589         next = task_thread_info(next_p);
 590
 591         if (has_secure_computing(prev) || has_secure_computing(next)) {
 592                 /* slow path here */
 593                 if (has_secure_computing(prev) &&
 594                     !has_secure_computing(next)) {
 595                         write_cr4(read_cr4() & ~X86_CR4_TSD);
 596                 } else if (!has_secure_computing(prev) &&
 597                            has_secure_computing(next))
 598                         write_cr4(read_cr4() | X86_CR4_TSD);
 599         }
 600 }
 601
 602 /*
 603  *      switch_to(x,yn) should switch tasks from x to y.
 604  *
 605  * We fsave/fwait so that an exception goes off at the right time
 606  * (as a call from the fsave or fwait in effect) rather than to
 607  * the wrong process. Lazy FP saving no longer makes any sense
 608  * with modern CPU's, and this simplifies a lot of things (SMP
 609  * and UP become the same).
 610  *
 611  * NOTE! We used to use the x86 hardware context switching. The
 612  * reason for not using it any more becomes apparent when you
 613  * try to recover gracefully from saved state that is no longer
 614  * valid (stale segment register values in particular). With the
 615  * hardware task-switch, there is no way to fix up bad state in
 616  * a reasonable manner.
 617  *
 618  * The fact that Intel documents the hardware task-switching to
 619  * be slow is a fairly red herring - this code is not noticeably
 620  * faster. However, there _is_ some room for improvement here,
 621  * so the performance issues may eventually be a valid point.
 622  * More important, however, is the fact that this allows us much
 623  * more flexibility.
 624  *
 625  * The return value (in %eax) will be the "prev" task after
 626  * the task-switch, and shows up in ret_from_fork in entry.S,
 627  * for example.
 628  */
 629 struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 630 {
 631         struct thread_struct *prev = &prev_p->thread,
 632                                  *next = &next_p->thread;
 633         int cpu = smp_processor_id();
 634         struct tss_struct *tss = &per_cpu(init_tss, cpu);
 635
 636         /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 637
 638         __unlazy_fpu(prev_p);
 639
 640         /*
 641          * Reload esp0.
 642          */
 643         load_esp0(tss, next);
 644
 645         /*
 646          * Save away %fs and %gs. No need to save %es and %ds, as
 647          * those are always kernel segments while inside the kernel.
 648          * Doing this before setting the new TLS descriptors avoids
 649          * the situation where we temporarily have non-reloadable
 650          * segments in %fs and %gs.  This could be an issue if the
 651          * NMI handler ever used %fs or %gs (it does not today), or
 652          * if the kernel is running inside of a hypervisor layer.
 653          */
 654         savesegment(fs, prev->fs);
 655         savesegment(gs, prev->gs);
 656
 657         /*
 658          * Load the per-thread Thread-Local Storage descriptor.
 659          */
 660         load_TLS(next, cpu);
 661
 662         /*
 663          * Restore %fs and %gs if needed.
 664          *
 665          * Glibc normally makes %fs be zero, and %gs is one of
 666          * the TLS segments.
 667          */
 668         if (unlikely(prev->fs | next->fs))
 669                 loadsegment(fs, next->fs);
 670
 671         if (prev->gs | next->gs)
 672                 loadsegment(gs, next->gs);
 673
 674         /*
 675          * Restore IOPL if needed.
 676          */
 677         if (unlikely(prev->iopl != next->iopl))
 678                 set_iopl_mask(next->iopl);
 679
 680         /*
 681          * Now maybe reload the debug registers
 682          */
 683         if (unlikely(next->debugreg[7])) {
 684                 set_debugreg(next->debugreg[0], 0);
 685                 set_debugreg(next->debugreg[1], 1);
 686                 set_debugreg(next->debugreg[2], 2);
 687                 set_debugreg(next->debugreg[3], 3);
 688                 /* no 4 and 5 */
 689                 set_debugreg(next->debugreg[6], 6);
 690                 set_debugreg(next->debugreg[7], 7);
 691         }
 692
 693         if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
 694                 handle_io_bitmap(next, tss);
 695
 696         disable_tsc(prev_p, next_p);
 697
 698         return prev_p;
 699 }
 700
 701 asmlinkage int sys_fork(struct pt_regs regs)
 702 {
 703         return do_fork(SIGCHLD, regs.esp, &regs, 0, NULL, NULL);
 704 }
 705
 706 asmlinkage int sys_clone(struct pt_regs regs)
 707 {
 708         unsigned long clone_flags;
 709         unsigned long newsp;
 710         int __user *parent_tidptr, *child_tidptr;
 711
 712         clone_flags = regs.ebx;
 713         newsp = regs.ecx;
 714         parent_tidptr = (int __user *)regs.edx;
 715         child_tidptr = (int __user *)regs.edi;
 716         if (!newsp)
 717                 newsp = regs.esp;
 718         return do_fork(clone_flags, newsp, &regs, 0, parent_tidptr, child_tidptr);
 719 }
 720
 721 /*
 722  * This is trivial, and on the face of it looks like it
 723  * could equally well be done in user mode.
 724  *
 725  * Not so, for quite unobvious reasons - register pressure.
 726  * In user mode vfork() cannot have a stack frame, and if
 727  * done by calling the "clone()" system call directly, you
 728  * do not have enough call-clobbered registers to hold all
 729  * the information you need.
 730  */
 731 asmlinkage int sys_vfork(struct pt_regs regs)
 732 {
 733         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.esp, &regs, 0, NULL, NULL);
 734 }
 735
 736 /*
 737  * sys_execve() executes a new program.
 738  */
 739 asmlinkage int sys_execve(struct pt_regs regs)
 740 {
 741         int error;
 742         char * filename;
 743
 744         filename = getname((char __user *) regs.ebx);
 745         error = PTR_ERR(filename);
 746         if (IS_ERR(filename))
 747                 goto out;
 748         error = do_execve(filename,
 749                         (char __user * __user *) regs.ecx,
 750                         (char __user * __user *) regs.edx,
 751                         &regs);
 752         if (error == 0) {
 753                 task_lock(current);
 754                 current->ptrace &= ~PT_DTRACE;
 755                 task_unlock(current);
 756                 /* Make sure we don't return using sysenter.. */
 757                 set_thread_flag(TIF_IRET);
 758         }
 759         putname(filename);
 760 out:
 761         return error;
 762 }
 763
 764 #define top_esp                (THREAD_SIZE - sizeof(unsigned long))
 765 #define top_ebp                (THREAD_SIZE - 2*sizeof(unsigned long))
 766
 767 unsigned long get_wchan(struct task_struct *p)
 768 {
 769         unsigned long ebp, esp, eip;
 770         unsigned long stack_page;
 771         int count = 0;
 772         if (!p || p == current || p->state == TASK_RUNNING)
 773                 return 0;
 774         stack_page = (unsigned long)p->thread_info;
 775         esp = p->thread.esp;
 776         if (!stack_page || esp < stack_page || esp > top_esp+stack_page)
 777                 return 0;
 778         /* include/asm-i386/system.h:switch_to() pushes ebp last. */
 779         ebp = *(unsigned long *) esp;
 780         do {
 781                 if (ebp < stack_page || ebp > top_ebp+stack_page)
 782                         return 0;
 783                 eip = *(unsigned long *) (ebp+4);
 784                 if (!in_sched_functions(eip))
 785                         return eip;
 786                 ebp = *(unsigned long *) ebp;
 787         } while (count++ < 16);
 788         return 0;
 789 }
 790 EXPORT_SYMBOL(get_wchan);
 791
 792 /*
 793  * sys_alloc_thread_area: get a yet unused TLS descriptor index.
 794  */
 795 static int get_free_idx(void)
 796 {
 797         struct thread_struct *t = &current->thread;
 798         int idx;
 799
 800         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
 801                 if (desc_empty(t->tls_array + idx))
 802                         return idx + GDT_ENTRY_TLS_MIN;
 803         return -ESRCH;
 804 }
 805
 806 /*
 807  * Set a given TLS descriptor:
 808  */
 809 asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
 810 {
 811         struct thread_struct *t = &current->thread;
 812         struct user_desc info;
 813         struct desc_struct *desc;
 814         int cpu, idx;
 815
 816         if (copy_from_user(&info, u_info, sizeof(info)))
 817                 return -EFAULT;
 818         idx = info.entry_number;
 819
 820         /*
 821          * index -1 means the kernel should try to find and
 822          * allocate an empty descriptor:
 823          */
 824         if (idx == -1) {
 825                 idx = get_free_idx();
 826                 if (idx < 0)
 827                         return idx;
 828                 if (put_user(idx, &u_info->entry_number))
 829                         return -EFAULT;
 830         }
 831
 832         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 833                 return -EINVAL;
 834
 835         desc = t->tls_array + idx - GDT_ENTRY_TLS_MIN;
 836
 837         /*
 838          * We must not get preempted while modifying the TLS.
 839          */
 840         cpu = get_cpu();
 841
 842         if (LDT_empty(&info)) {
 843                 desc->a = 0;
 844                 desc->b = 0;
 845         } else {
 846                 desc->a = LDT_entry_a(&info);
 847                 desc->b = LDT_entry_b(&info);
 848         }
 849         load_TLS(t, cpu);
 850
 851         put_cpu();
 852
 853         return 0;
 854 }
 855
 856 /*
 857  * Get the current Thread-Local Storage area:
 858  */
 859
 860 #define GET_BASE(desc) ( \
 861         (((desc)->a >> 16) & 0x0000ffff) | \
 862         (((desc)->b << 16) & 0x00ff0000) | \
 863         ( (desc)->b        & 0xff000000)   )
 864
 865 #define GET_LIMIT(desc) ( \
 866         ((desc)->a & 0x0ffff) | \
 867          ((desc)->b & 0xf0000) )
 868
 869 #define GET_32BIT(desc)         (((desc)->b >> 22) & 1)
 870 #define GET_CONTENTS(desc)      (((desc)->b >> 10) & 3)
 871 #define GET_WRITABLE(desc)      (((desc)->b >>  9) & 1)
 872 #define GET_LIMIT_PAGES(desc)   (((desc)->b >> 23) & 1)
 873 #define GET_PRESENT(desc)       (((desc)->b >> 15) & 1)
 874 #define GET_USEABLE(desc)       (((desc)->b >> 20) & 1)
 875
 876 asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
 877 {
 878         struct user_desc info;
 879         struct desc_struct *desc;
 880         int idx;
 881
 882         if (get_user(idx, &u_info->entry_number))
 883                 return -EFAULT;
 884         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 885                 return -EINVAL;
 886
 887         memset(&info, 0, sizeof(info));
 888
 889         desc = current->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
 890
 891         info.entry_number = idx;
 892         info.base_addr = GET_BASE(desc);
 893         info.limit = GET_LIMIT(desc);
 894         info.seg_32bit = GET_32BIT(desc);
 895         info.contents = GET_CONTENTS(desc);
 896         info.read_exec_only = !GET_WRITABLE(desc);
 897         info.limit_in_pages = GET_LIMIT_PAGES(desc);
 898         info.seg_not_present = !GET_PRESENT(desc);
 899         info.useable = GET_USEABLE(desc);
 900
 901         if (copy_to_user(u_info, &info, sizeof(info)))
 902                 return -EFAULT;
 903         return 0;
 904 }
 905
 906 unsigned long arch_align_stack(unsigned long sp)
 907 {
 908         if (randomize_va_space)
 909                 sp -= get_random_int() % 8192;
 910         return sp & ~0xf;
 911 }