arch/x86/kernel/process_32.c

   1 /*
   2  *  Copyright (C) 1995  Linus Torvalds
   3  *
   4  *  Pentium III FXSR, SSE support
   5  *      Gareth Hughes <gareth@valinux.com>, May 2000
   6  */
   7
   8 /*
   9  * This file handles the architecture-dependent parts of process handling..
  10  */
  11
  12 #include <stdarg.h>
  13
  14 #include <linux/cpu.h>
  15 #include <linux/errno.h>
  16 #include <linux/sched.h>
  17 #include <linux/fs.h>
  18 #include <linux/kernel.h>
  19 #include <linux/mm.h>
  20 #include <linux/elfcore.h>
  21 #include <linux/smp.h>
  22 #include <linux/stddef.h>
  23 #include <linux/slab.h>
  24 #include <linux/vmalloc.h>
  25 #include <linux/user.h>
  26 #include <linux/interrupt.h>
  27 #include <linux/utsname.h>
  28 #include <linux/delay.h>
  29 #include <linux/reboot.h>
  30 #include <linux/init.h>
  31 #include <linux/mc146818rtc.h>
  32 #include <linux/module.h>
  33 #include <linux/kallsyms.h>
  34 #include <linux/ptrace.h>
  35 #include <linux/random.h>
  36 #include <linux/personality.h>
  37 #include <linux/tick.h>
  38 #include <linux/percpu.h>
  39 #include <linux/prctl.h>
  40 #include <linux/dmi.h>
  41 #include <linux/ftrace.h>
  42 #include <linux/uaccess.h>
  43 #include <linux/io.h>
  44 #include <linux/kdebug.h>
  45
  46 #include <asm/pgtable.h>
  47 #include <asm/system.h>
  48 #include <asm/ldt.h>
  49 #include <asm/processor.h>
  50 #include <asm/i387.h>
  51 #include <asm/desc.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 #include <asm/idle.h>
  61 #include <asm/syscalls.h>
  62 #include <asm/ds.h>
  63
  64 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
  65
  66 DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
  67 EXPORT_PER_CPU_SYMBOL(current_task);
  68
  69 DEFINE_PER_CPU(int, cpu_number);
  70 EXPORT_PER_CPU_SYMBOL(cpu_number);
  71
  72 /*
  73  * Return saved PC of a blocked thread.
  74  */
  75 unsigned long thread_saved_pc(struct task_struct *tsk)
  76 {
  77         return ((unsigned long *)tsk->thread.sp)[3];
  78 }
  79
  80 #ifndef CONFIG_SMP
  81 static inline void play_dead(void)
  82 {
  83         BUG();
  84 }
  85 #endif
  86
  87 /*
  88  * The idle thread. There's no useful work to be
  89  * done, so just try to conserve power and have a
  90  * low exit latency (ie sit in a loop waiting for
  91  * somebody to say that they'd like to reschedule)
  92  */
  93 void cpu_idle(void)
  94 {
  95         int cpu = smp_processor_id();
  96
  97         current_thread_info()->status |= TS_POLLING;
  98
  99         /* endless idle loop with no priority at all */
 100         while (1) {
 101                 tick_nohz_stop_sched_tick(1);
 102                 while (!need_resched()) {
 103
 104                         check_pgt_cache();
 105                         rmb();
 106
 107                         if (rcu_pending(cpu))
 108                                 rcu_check_callbacks(cpu, 0);
 109
 110                         if (cpu_is_offline(cpu))
 111                                 play_dead();
 112
 113                         local_irq_disable();
 114                         __get_cpu_var(irq_stat).idle_timestamp = jiffies;
 115                         /* Don't trace irqs off for idle */
 116                         stop_critical_timings();
 117                         pm_idle();
 118                         start_critical_timings();
 119                 }
 120                 tick_nohz_restart_sched_tick();
 121                 preempt_enable_no_resched();
 122                 schedule();
 123                 preempt_disable();
 124         }
 125 }
 126
 127 void __show_regs(struct pt_regs *regs, int all)
 128 {
 129         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 130         unsigned long d0, d1, d2, d3, d6, d7;
 131         unsigned long sp;
 132         unsigned short ss, gs;
 133         const char *board;
 134
 135         if (user_mode_vm(regs)) {
 136                 sp = regs->sp;
 137                 ss = regs->ss & 0xffff;
 138                 savesegment(gs, gs);
 139         } else {
 140                 sp = (unsigned long) (&regs->sp);
 141                 savesegment(ss, ss);
 142                 savesegment(gs, gs);
 143         }
 144
 145         printk("\n");
 146
 147         board = dmi_get_system_info(DMI_PRODUCT_NAME);
 148         if (!board)
 149                 board = "";
 150         printk("Pid: %d, comm: %s %s (%s %.*s) %s\n",
 151                         task_pid_nr(current), current->comm,
 152                         print_tainted(), init_utsname()->release,
 153                         (int)strcspn(init_utsname()->version, " "),
 154                         init_utsname()->version, board);
 155
 156         printk("EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
 157                         (u16)regs->cs, regs->ip, regs->flags,
 158                         smp_processor_id());
 159         print_symbol("EIP is at %s\n", regs->ip);
 160
 161         printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
 162                 regs->ax, regs->bx, regs->cx, regs->dx);
 163         printk("ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
 164                 regs->si, regs->di, regs->bp, sp);
 165         printk(" DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
 166                (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss);
 167
 168         if (!all)
 169                 return;
 170
 171         cr0 = read_cr0();
 172         cr2 = read_cr2();
 173         cr3 = read_cr3();
 174         cr4 = read_cr4_safe();
 175         printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
 176                         cr0, cr2, cr3, cr4);
 177
 178         get_debugreg(d0, 0);
 179         get_debugreg(d1, 1);
 180         get_debugreg(d2, 2);
 181         get_debugreg(d3, 3);
 182         printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
 183                         d0, d1, d2, d3);
 184
 185         get_debugreg(d6, 6);
 186         get_debugreg(d7, 7);
 187         printk("DR6: %08lx DR7: %08lx\n",
 188                         d6, d7);
 189 }
 190
 191 void show_regs(struct pt_regs *regs)
 192 {
 193         __show_regs(regs, 1);
 194         show_trace(NULL, regs, &regs->sp, regs->bp);
 195 }
 196
 197 /*
 198  * This gets run with %bx containing the
 199  * function to call, and %dx containing
 200  * the "args".
 201  */
 202 extern void kernel_thread_helper(void);
 203
 204 /*
 205  * Create a kernel thread
 206  */
 207 int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
 208 {
 209         struct pt_regs regs;
 210
 211         memset(&regs, 0, sizeof(regs));
 212
 213         regs.bx = (unsigned long) fn;
 214         regs.dx = (unsigned long) arg;
 215
 216         regs.ds = __USER_DS;
 217         regs.es = __USER_DS;
 218         regs.fs = __KERNEL_PERCPU;
 219         regs.orig_ax = -1;
 220         regs.ip = (unsigned long) kernel_thread_helper;
 221         regs.cs = __KERNEL_CS | get_kernel_rpl();
 222         regs.flags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
 223
 224         /* Ok, create the new process.. */
 225         return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
 226 }
 227 EXPORT_SYMBOL(kernel_thread);
 228
 229 /*
 230  * Free current thread data structures etc..
 231  */
 232 void exit_thread(void)
 233 {
 234         /* The process may have allocated an io port bitmap... nuke it. */
 235         if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
 236                 struct task_struct *tsk = current;
 237                 struct thread_struct *t = &tsk->thread;
 238                 int cpu = get_cpu();
 239                 struct tss_struct *tss = &per_cpu(init_tss, cpu);
 240
 241                 kfree(t->io_bitmap_ptr);
 242                 t->io_bitmap_ptr = NULL;
 243                 clear_thread_flag(TIF_IO_BITMAP);
 244                 /*
 245                  * Careful, clear this in the TSS too:
 246                  */
 247                 memset(tss->io_bitmap, 0xff, tss->io_bitmap_max);
 248                 t->io_bitmap_max = 0;
 249                 tss->io_bitmap_owner = NULL;
 250                 tss->io_bitmap_max = 0;
 251                 tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 252                 put_cpu();
 253         }
 254
 255         ds_exit_thread(current);
 256 }
 257
 258 void flush_thread(void)
 259 {
 260         struct task_struct *tsk = current;
 261
 262         tsk->thread.debugreg0 = 0;
 263         tsk->thread.debugreg1 = 0;
 264         tsk->thread.debugreg2 = 0;
 265         tsk->thread.debugreg3 = 0;
 266         tsk->thread.debugreg6 = 0;
 267         tsk->thread.debugreg7 = 0;
 268         memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
 269         clear_tsk_thread_flag(tsk, TIF_DEBUG);
 270         /*
 271          * Forget coprocessor state..
 272          */
 273         tsk->fpu_counter = 0;
 274         clear_fpu(tsk);
 275         clear_used_math();
 276 }
 277
 278 void release_thread(struct task_struct *dead_task)
 279 {
 280         BUG_ON(dead_task->mm);
 281         release_vm86_irqs(dead_task);
 282 }
 283
 284 /*
 285  * This gets called before we allocate a new thread and copy
 286  * the current task into it.
 287  */
 288 void prepare_to_copy(struct task_struct *tsk)
 289 {
 290         unlazy_fpu(tsk);
 291 }
 292
 293 int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 294         unsigned long unused,
 295         struct task_struct *p, struct pt_regs *regs)
 296 {
 297         struct pt_regs *childregs;
 298         struct task_struct *tsk;
 299         int err;
 300
 301         childregs = task_pt_regs(p);
 302         *childregs = *regs;
 303         childregs->ax = 0;
 304         childregs->sp = sp;
 305
 306         p->thread.sp = (unsigned long) childregs;
 307         p->thread.sp0 = (unsigned long) (childregs+1);
 308
 309         p->thread.ip = (unsigned long) ret_from_fork;
 310
 311         savesegment(gs, p->thread.gs);
 312
 313         tsk = current;
 314         if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
 315                 p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
 316                                                 IO_BITMAP_BYTES, GFP_KERNEL);
 317                 if (!p->thread.io_bitmap_ptr) {
 318                         p->thread.io_bitmap_max = 0;
 319                         return -ENOMEM;
 320                 }
 321                 set_tsk_thread_flag(p, TIF_IO_BITMAP);
 322         }
 323
 324         err = 0;
 325
 326         /*
 327          * Set a new TLS for the child thread?
 328          */
 329         if (clone_flags & CLONE_SETTLS)
 330                 err = do_set_thread_area(p, -1,
 331                         (struct user_desc __user *)childregs->si, 0);
 332
 333         if (err && p->thread.io_bitmap_ptr) {
 334                 kfree(p->thread.io_bitmap_ptr);
 335                 p->thread.io_bitmap_max = 0;
 336         }
 337
 338         ds_copy_thread(p, current);
 339
 340         clear_tsk_thread_flag(p, TIF_DEBUGCTLMSR);
 341         p->thread.debugctlmsr = 0;
 342
 343         return err;
 344 }
 345
 346 void
 347 start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 348 {
 349         __asm__("movl %0, %%gs" : : "r"(0));
 350         regs->fs                = 0;
 351         set_fs(USER_DS);
 352         regs->ds                = __USER_DS;
 353         regs->es                = __USER_DS;
 354         regs->ss                = __USER_DS;
 355         regs->cs                = __USER_CS;
 356         regs->ip                = new_ip;
 357         regs->sp                = new_sp;
 358         /*
 359          * Free the old FP and other extended state
 360          */
 361         free_thread_xstate(current);
 362 }
 363 EXPORT_SYMBOL_GPL(start_thread);
 364
 365 static void hard_disable_TSC(void)
 366 {
 367         write_cr4(read_cr4() | X86_CR4_TSD);
 368 }
 369
 370 void disable_TSC(void)
 371 {
 372         preempt_disable();
 373         if (!test_and_set_thread_flag(TIF_NOTSC))
 374                 /*
 375                  * Must flip the CPU state synchronously with
 376                  * TIF_NOTSC in the current running context.
 377                  */
 378                 hard_disable_TSC();
 379         preempt_enable();
 380 }
 381
 382 static void hard_enable_TSC(void)
 383 {
 384         write_cr4(read_cr4() & ~X86_CR4_TSD);
 385 }
 386
 387 static void enable_TSC(void)
 388 {
 389         preempt_disable();
 390         if (test_and_clear_thread_flag(TIF_NOTSC))
 391                 /*
 392                  * Must flip the CPU state synchronously with
 393                  * TIF_NOTSC in the current running context.
 394                  */
 395                 hard_enable_TSC();
 396         preempt_enable();
 397 }
 398
 399 int get_tsc_mode(unsigned long adr)
 400 {
 401         unsigned int val;
 402
 403         if (test_thread_flag(TIF_NOTSC))
 404                 val = PR_TSC_SIGSEGV;
 405         else
 406                 val = PR_TSC_ENABLE;
 407
 408         return put_user(val, (unsigned int __user *)adr);
 409 }
 410
 411 int set_tsc_mode(unsigned int val)
 412 {
 413         if (val == PR_TSC_SIGSEGV)
 414                 disable_TSC();
 415         else if (val == PR_TSC_ENABLE)
 416                 enable_TSC();
 417         else
 418                 return -EINVAL;
 419
 420         return 0;
 421 }
 422
 423 static noinline void
 424 __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 425                  struct tss_struct *tss)
 426 {
 427         struct thread_struct *prev, *next;
 428
 429         prev = &prev_p->thread;
 430         next = &next_p->thread;
 431
 432         if (test_tsk_thread_flag(next_p, TIF_DS_AREA_MSR) ||
 433             test_tsk_thread_flag(prev_p, TIF_DS_AREA_MSR))
 434                 ds_switch_to(prev_p, next_p);
 435         else if (next->debugctlmsr != prev->debugctlmsr)
 436                 update_debugctlmsr(next->debugctlmsr);
 437
 438         if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
 439                 set_debugreg(next->debugreg0, 0);
 440                 set_debugreg(next->debugreg1, 1);
 441                 set_debugreg(next->debugreg2, 2);
 442                 set_debugreg(next->debugreg3, 3);
 443                 /* no 4 and 5 */
 444                 set_debugreg(next->debugreg6, 6);
 445                 set_debugreg(next->debugreg7, 7);
 446         }
 447
 448         if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
 449             test_tsk_thread_flag(next_p, TIF_NOTSC)) {
 450                 /* prev and next are different */
 451                 if (test_tsk_thread_flag(next_p, TIF_NOTSC))
 452                         hard_disable_TSC();
 453                 else
 454                         hard_enable_TSC();
 455         }
 456
 457         if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
 458                 /*
 459                  * Disable the bitmap via an invalid offset. We still cache
 460                  * the previous bitmap owner and the IO bitmap contents:
 461                  */
 462                 tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 463                 return;
 464         }
 465
 466         if (likely(next == tss->io_bitmap_owner)) {
 467                 /*
 468                  * Previous owner of the bitmap (hence the bitmap content)
 469                  * matches the next task, we dont have to do anything but
 470                  * to set a valid offset in the TSS:
 471                  */
 472                 tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET;
 473                 return;
 474         }
 475         /*
 476          * Lazy TSS's I/O bitmap copy. We set an invalid offset here
 477          * and we let the task to get a GPF in case an I/O instruction
 478          * is performed.  The handler of the GPF will verify that the
 479          * faulting task has a valid I/O bitmap and, it true, does the
 480          * real copy and restart the instruction.  This will save us
 481          * redundant copies when the currently switched task does not
 482          * perform any I/O during its timeslice.
 483          */
 484         tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 485 }
 486
 487 /*
 488  *      switch_to(x,yn) should switch tasks from x to y.
 489  *
 490  * We fsave/fwait so that an exception goes off at the right time
 491  * (as a call from the fsave or fwait in effect) rather than to
 492  * the wrong process. Lazy FP saving no longer makes any sense
 493  * with modern CPU's, and this simplifies a lot of things (SMP
 494  * and UP become the same).
 495  *
 496  * NOTE! We used to use the x86 hardware context switching. The
 497  * reason for not using it any more becomes apparent when you
 498  * try to recover gracefully from saved state that is no longer
 499  * valid (stale segment register values in particular). With the
 500  * hardware task-switch, there is no way to fix up bad state in
 501  * a reasonable manner.
 502  *
 503  * The fact that Intel documents the hardware task-switching to
 504  * be slow is a fairly red herring - this code is not noticeably
 505  * faster. However, there _is_ some room for improvement here,
 506  * so the performance issues may eventually be a valid point.
 507  * More important, however, is the fact that this allows us much
 508  * more flexibility.
 509  *
 510  * The return value (in %ax) will be the "prev" task after
 511  * the task-switch, and shows up in ret_from_fork in entry.S,
 512  * for example.
 513  */
 514 __notrace_funcgraph struct task_struct *
 515 __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 516 {
 517         struct thread_struct *prev = &prev_p->thread,
 518                                  *next = &next_p->thread;
 519         int cpu = smp_processor_id();
 520         struct tss_struct *tss = &per_cpu(init_tss, cpu);
 521
 522         /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 523
 524         __unlazy_fpu(prev_p);
 525
 526
 527         /* we're going to use this soon, after a few expensive things */
 528         if (next_p->fpu_counter > 5)
 529                 prefetch(next->xstate);
 530
 531         /*
 532          * Reload esp0.
 533          */
 534         load_sp0(tss, next);
 535
 536         /*
 537          * Save away %gs. No need to save %fs, as it was saved on the
 538          * stack on entry.  No need to save %es and %ds, as those are
 539          * always kernel segments while inside the kernel.  Doing this
 540          * before setting the new TLS descriptors avoids the situation
 541          * where we temporarily have non-reloadable segments in %fs
 542          * and %gs.  This could be an issue if the NMI handler ever
 543          * used %fs or %gs (it does not today), or if the kernel is
 544          * running inside of a hypervisor layer.
 545          */
 546         savesegment(gs, prev->gs);
 547
 548         /*
 549          * Load the per-thread Thread-Local Storage descriptor.
 550          */
 551         load_TLS(next, cpu);
 552
 553         /*
 554          * Restore IOPL if needed.  In normal use, the flags restore
 555          * in the switch assembly will handle this.  But if the kernel
 556          * is running virtualized at a non-zero CPL, the popf will
 557          * not restore flags, so it must be done in a separate step.
 558          */
 559         if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
 560                 set_iopl_mask(next->iopl);
 561
 562         /*
 563          * Now maybe handle debug registers and/or IO bitmaps
 564          */
 565         if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
 566                      task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
 567                 __switch_to_xtra(prev_p, next_p, tss);
 568
 569         /*
 570          * Leave lazy mode, flushing any hypercalls made here.
 571          * This must be done before restoring TLS segments so
 572          * the GDT and LDT are properly updated, and must be
 573          * done before math_state_restore, so the TS bit is up
 574          * to date.
 575          */
 576         arch_leave_lazy_cpu_mode();
 577
 578         /* If the task has used fpu the last 5 timeslices, just do a full
 579          * restore of the math state immediately to avoid the trap; the
 580          * chances of needing FPU soon are obviously high now
 581          *
 582          * tsk_used_math() checks prevent calling math_state_restore(),
 583          * which can sleep in the case of !tsk_used_math()
 584          */
 585         if (tsk_used_math(next_p) && next_p->fpu_counter > 5)
 586                 math_state_restore();
 587
 588         /*
 589          * Restore %gs if needed (which is common)
 590          */
 591         if (prev->gs | next->gs)
 592                 loadsegment(gs, next->gs);
 593
 594         x86_write_percpu(current_task, next_p);
 595
 596         return prev_p;
 597 }
 598
 599 asmlinkage int sys_fork(struct pt_regs regs)
 600 {
 601         return do_fork(SIGCHLD, regs.sp, &regs, 0, NULL, NULL);
 602 }
 603
 604 asmlinkage int sys_clone(struct pt_regs regs)
 605 {
 606         unsigned long clone_flags;
 607         unsigned long newsp;
 608         int __user *parent_tidptr, *child_tidptr;
 609
 610         clone_flags = regs.bx;
 611         newsp = regs.cx;
 612         parent_tidptr = (int __user *)regs.dx;
 613         child_tidptr = (int __user *)regs.di;
 614         if (!newsp)
 615                 newsp = regs.sp;
 616         return do_fork(clone_flags, newsp, &regs, 0, parent_tidptr, child_tidptr);
 617 }
 618
 619 /*
 620  * This is trivial, and on the face of it looks like it
 621  * could equally well be done in user mode.
 622  *
 623  * Not so, for quite unobvious reasons - register pressure.
 624  * In user mode vfork() cannot have a stack frame, and if
 625  * done by calling the "clone()" system call directly, you
 626  * do not have enough call-clobbered registers to hold all
 627  * the information you need.
 628  */
 629 asmlinkage int sys_vfork(struct pt_regs regs)
 630 {
 631         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.sp, &regs, 0, NULL, NULL);
 632 }
 633
 634 /*
 635  * sys_execve() executes a new program.
 636  */
 637 asmlinkage int sys_execve(struct pt_regs regs)
 638 {
 639         int error;
 640         char *filename;
 641
 642         filename = getname((char __user *) regs.bx);
 643         error = PTR_ERR(filename);
 644         if (IS_ERR(filename))
 645                 goto out;
 646         error = do_execve(filename,
 647                         (char __user * __user *) regs.cx,
 648                         (char __user * __user *) regs.dx,
 649                         &regs);
 650         if (error == 0) {
 651                 /* Make sure we don't return using sysenter.. */
 652                 set_thread_flag(TIF_IRET);
 653         }
 654         putname(filename);
 655 out:
 656         return error;
 657 }
 658
 659 #define top_esp                (THREAD_SIZE - sizeof(unsigned long))
 660 #define top_ebp                (THREAD_SIZE - 2*sizeof(unsigned long))
 661
 662 unsigned long get_wchan(struct task_struct *p)
 663 {
 664         unsigned long bp, sp, ip;
 665         unsigned long stack_page;
 666         int count = 0;
 667         if (!p || p == current || p->state == TASK_RUNNING)
 668                 return 0;
 669         stack_page = (unsigned long)task_stack_page(p);
 670         sp = p->thread.sp;
 671         if (!stack_page || sp < stack_page || sp > top_esp+stack_page)
 672                 return 0;
 673         /* include/asm-i386/system.h:switch_to() pushes bp last. */
 674         bp = *(unsigned long *) sp;
 675         do {
 676                 if (bp < stack_page || bp > top_ebp+stack_page)
 677                         return 0;
 678                 ip = *(unsigned long *) (bp+4);
 679                 if (!in_sched_functions(ip))
 680                         return ip;
 681                 bp = *(unsigned long *) bp;
 682         } while (count++ < 16);
 683         return 0;
 684 }
 685
 686 unsigned long arch_align_stack(unsigned long sp)
 687 {
 688         if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
 689                 sp -= get_random_int() % 8192;
 690         return sp & ~0xf;
 691 }
 692
 693 unsigned long arch_randomize_brk(struct mm_struct *mm)
 694 {
 695         unsigned long range_end = mm->brk + 0x02000000;
 696         return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
 697 }