git.oblomov.eu Git - linux-2.6/blob - arch/ppc64/kernel/process.c

   1 /*
   2  *  linux/arch/ppc64/kernel/process.c
   3  *
   4  *  Derived from "arch/i386/kernel/process.c"
   5  *    Copyright (C) 1995  Linus Torvalds
   6  *
   7  *  Updated and modified by Cort Dougan (cort@cs.nmt.edu) and
   8  *  Paul Mackerras (paulus@cs.anu.edu.au)
   9  *
  10  *  PowerPC version
  11  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  12  *
  13  *  This program is free software; you can redistribute it and/or
  14  *  modify it under the terms of the GNU General Public License
  15  *  as published by the Free Software Foundation; either version
  16  *  2 of the License, or (at your option) any later version.
  17  */
  18
  19 #include <linux/config.h>
  20 #include <linux/module.h>
  21 #include <linux/errno.h>
  22 #include <linux/sched.h>
  23 #include <linux/kernel.h>
  24 #include <linux/mm.h>
  25 #include <linux/smp.h>
  26 #include <linux/smp_lock.h>
  27 #include <linux/stddef.h>
  28 #include <linux/unistd.h>
  29 #include <linux/slab.h>
  30 #include <linux/user.h>
  31 #include <linux/elf.h>
  32 #include <linux/init.h>
  33 #include <linux/init_task.h>
  34 #include <linux/prctl.h>
  35 #include <linux/ptrace.h>
  36 #include <linux/kallsyms.h>
  37 #include <linux/interrupt.h>
  38 #include <linux/utsname.h>
  39
  40 #include <asm/pgtable.h>
  41 #include <asm/uaccess.h>
  42 #include <asm/system.h>
  43 #include <asm/io.h>
  44 #include <asm/processor.h>
  45 #include <asm/mmu.h>
  46 #include <asm/mmu_context.h>
  47 #include <asm/prom.h>
  48 #include <asm/ppcdebug.h>
  49 #include <asm/machdep.h>
  50 #include <asm/iSeries/HvCallHpt.h>
  51 #include <asm/cputable.h>
  52 #include <asm/sections.h>
  53 #include <asm/tlbflush.h>
  54 #include <asm/time.h>
  55
  56 #ifndef CONFIG_SMP
  57 struct task_struct *last_task_used_math = NULL;
  58 struct task_struct *last_task_used_altivec = NULL;
  59 #endif
  60
  61 /*
  62  * Make sure the floating-point register state in the
  63  * the thread_struct is up to date for task tsk.
  64  */
  65 void flush_fp_to_thread(struct task_struct *tsk)
  66 {
  67         if (tsk->thread.regs) {
  68                 /*
  69                  * We need to disable preemption here because if we didn't,
  70                  * another process could get scheduled after the regs->msr
  71                  * test but before we have finished saving the FP registers
  72                  * to the thread_struct.  That process could take over the
  73                  * FPU, and then when we get scheduled again we would store
  74                  * bogus values for the remaining FP registers.
  75                  */
  76                 preempt_disable();
  77                 if (tsk->thread.regs->msr & MSR_FP) {
  78 #ifdef CONFIG_SMP
  79                         /*
  80                          * This should only ever be called for current or
  81                          * for a stopped child process.  Since we save away
  82                          * the FP register state on context switch on SMP,
  83                          * there is something wrong if a stopped child appears
  84                          * to still have its FP state in the CPU registers.
  85                          */
  86                         BUG_ON(tsk != current);
  87 #endif
  88                         giveup_fpu(current);
  89                 }
  90                 preempt_enable();
  91         }
  92 }
  93
  94 void enable_kernel_fp(void)
  95 {
  96         WARN_ON(preemptible());
  97
  98 #ifdef CONFIG_SMP
  99         if (current->thread.regs && (current->thread.regs->msr & MSR_FP))
 100                 giveup_fpu(current);
 101         else
 102                 giveup_fpu(NULL);       /* just enables FP for kernel */
 103 #else
 104         giveup_fpu(last_task_used_math);
 105 #endif /* CONFIG_SMP */
 106 }
 107 EXPORT_SYMBOL(enable_kernel_fp);
 108
 109 int dump_task_fpu(struct task_struct *tsk, elf_fpregset_t *fpregs)
 110 {
 111         if (!tsk->thread.regs)
 112                 return 0;
 113         flush_fp_to_thread(current);
 114
 115         memcpy(fpregs, &tsk->thread.fpr[0], sizeof(*fpregs));
 116
 117         return 1;
 118 }
 119
 120 #ifdef CONFIG_ALTIVEC
 121
 122 void enable_kernel_altivec(void)
 123 {
 124         WARN_ON(preemptible());
 125
 126 #ifdef CONFIG_SMP
 127         if (current->thread.regs && (current->thread.regs->msr & MSR_VEC))
 128                 giveup_altivec(current);
 129         else
 130                 giveup_altivec(NULL);   /* just enables FP for kernel */
 131 #else
 132         giveup_altivec(last_task_used_altivec);
 133 #endif /* CONFIG_SMP */
 134 }
 135 EXPORT_SYMBOL(enable_kernel_altivec);
 136
 137 /*
 138  * Make sure the VMX/Altivec register state in the
 139  * the thread_struct is up to date for task tsk.
 140  */
 141 void flush_altivec_to_thread(struct task_struct *tsk)
 142 {
 143         if (tsk->thread.regs) {
 144                 preempt_disable();
 145                 if (tsk->thread.regs->msr & MSR_VEC) {
 146 #ifdef CONFIG_SMP
 147                         BUG_ON(tsk != current);
 148 #endif
 149                         giveup_altivec(current);
 150                 }
 151                 preempt_enable();
 152         }
 153 }
 154
 155 int dump_task_altivec(struct pt_regs *regs, elf_vrregset_t *vrregs)
 156 {
 157         flush_altivec_to_thread(current);
 158         memcpy(vrregs, &current->thread.vr[0], sizeof(*vrregs));
 159         return 1;
 160 }
 161
 162 #endif /* CONFIG_ALTIVEC */
 163
 164 DEFINE_PER_CPU(struct cpu_usage, cpu_usage_array);
 165
 166 struct task_struct *__switch_to(struct task_struct *prev,
 167                                 struct task_struct *new)
 168 {
 169         struct thread_struct *new_thread, *old_thread;
 170         unsigned long flags;
 171         struct task_struct *last;
 172
 173 #ifdef CONFIG_SMP
 174         /* avoid complexity of lazy save/restore of fpu
 175          * by just saving it every time we switch out if
 176          * this task used the fpu during the last quantum.
 177          *
 178          * If it tries to use the fpu again, it'll trap and
 179          * reload its fp regs.  So we don't have to do a restore
 180          * every switch, just a save.
 181          *  -- Cort
 182          */
 183         if (prev->thread.regs && (prev->thread.regs->msr & MSR_FP))
 184                 giveup_fpu(prev);
 185 #ifdef CONFIG_ALTIVEC
 186         if (prev->thread.regs && (prev->thread.regs->msr & MSR_VEC))
 187                 giveup_altivec(prev);
 188 #endif /* CONFIG_ALTIVEC */
 189 #endif /* CONFIG_SMP */
 190
 191 #if defined(CONFIG_ALTIVEC) && !defined(CONFIG_SMP)
 192         /* Avoid the trap.  On smp this this never happens since
 193          * we don't set last_task_used_altivec -- Cort
 194          */
 195         if (new->thread.regs && last_task_used_altivec == new)
 196                 new->thread.regs->msr |= MSR_VEC;
 197 #endif /* CONFIG_ALTIVEC */
 198
 199         flush_tlb_pending();
 200
 201         new_thread = &new->thread;
 202         old_thread = &current->thread;
 203
 204 /* Collect purr utilization data per process and per processor wise */
 205 /* purr is nothing but processor time base                          */
 206
 207 #if defined(CONFIG_PPC_PSERIES)
 208         if (cur_cpu_spec->firmware_features & FW_FEATURE_SPLPAR) {
 209                 struct cpu_usage *cu = &__get_cpu_var(cpu_usage_array);
 210                 long unsigned start_tb, current_tb;
 211                 start_tb = old_thread->start_tb;
 212                 cu->current_tb = current_tb = mfspr(SPRN_PURR);
 213                 old_thread->accum_tb += (current_tb - start_tb);
 214                 new_thread->start_tb = current_tb;
 215         }
 216 #endif
 217
 218
 219         local_irq_save(flags);
 220         last = _switch(old_thread, new_thread);
 221
 222         local_irq_restore(flags);
 223
 224         return last;
 225 }
 226
 227 static int instructions_to_print = 16;
 228
 229 static void show_instructions(struct pt_regs *regs)
 230 {
 231         int i;
 232         unsigned long pc = regs->nip - (instructions_to_print * 3 / 4 *
 233                         sizeof(int));
 234
 235         printk("Instruction dump:");
 236
 237         for (i = 0; i < instructions_to_print; i++) {
 238                 int instr;
 239
 240                 if (!(i % 8))
 241                         printk("\n");
 242
 243                 if (((REGION_ID(pc) != KERNEL_REGION_ID) &&
 244                      (REGION_ID(pc) != VMALLOC_REGION_ID)) ||
 245                      __get_user(instr, (unsigned int *)pc)) {
 246                         printk("XXXXXXXX ");
 247                 } else {
 248                         if (regs->nip == pc)
 249                                 printk("<%08x> ", instr);
 250                         else
 251                                 printk("%08x ", instr);
 252                 }
 253
 254                 pc += sizeof(int);
 255         }
 256
 257         printk("\n");
 258 }
 259
 260 void show_regs(struct pt_regs * regs)
 261 {
 262         int i;
 263         unsigned long trap;
 264
 265         printk("NIP: %016lX XER: %08X LR: %016lX CTR: %016lX\n",
 266                regs->nip, (unsigned int)regs->xer, regs->link, regs->ctr);
 267         printk("REGS: %p TRAP: %04lx   %s  (%s)\n",
 268                regs, regs->trap, print_tainted(), system_utsname.release);
 269         printk("MSR: %016lx EE: %01x PR: %01x FP: %01x ME: %01x "
 270                "IR/DR: %01x%01x CR: %08X\n",
 271                regs->msr, regs->msr&MSR_EE ? 1 : 0, regs->msr&MSR_PR ? 1 : 0,
 272                regs->msr & MSR_FP ? 1 : 0,regs->msr&MSR_ME ? 1 : 0,
 273                regs->msr&MSR_IR ? 1 : 0,
 274                regs->msr&MSR_DR ? 1 : 0,
 275                (unsigned int)regs->ccr);
 276         trap = TRAP(regs);
 277         printk("DAR: %016lx DSISR: %016lx\n", regs->dar, regs->dsisr);
 278         printk("TASK: %p[%d] '%s' THREAD: %p",
 279                current, current->pid, current->comm, current->thread_info);
 280
 281 #ifdef CONFIG_SMP
 282         printk(" CPU: %d", smp_processor_id());
 283 #endif /* CONFIG_SMP */
 284
 285         for (i = 0; i < 32; i++) {
 286                 if ((i % 4) == 0) {
 287                         printk("\n" KERN_INFO "GPR%02d: ", i);
 288                 }
 289
 290                 printk("%016lX ", regs->gpr[i]);
 291                 if (i == 13 && !FULL_REGS(regs))
 292                         break;
 293         }
 294         printk("\n");
 295         /*
 296          * Lookup NIP late so we have the best change of getting the
 297          * above info out without failing
 298          */
 299         printk("NIP [%016lx] ", regs->nip);
 300         print_symbol("%s\n", regs->nip);
 301         printk("LR [%016lx] ", regs->link);
 302         print_symbol("%s\n", regs->link);
 303         show_stack(current, (unsigned long *)regs->gpr[1]);
 304         if (!user_mode(regs))
 305                 show_instructions(regs);
 306 }
 307
 308 void exit_thread(void)
 309 {
 310 #ifndef CONFIG_SMP
 311         if (last_task_used_math == current)
 312                 last_task_used_math = NULL;
 313 #ifdef CONFIG_ALTIVEC
 314         if (last_task_used_altivec == current)
 315                 last_task_used_altivec = NULL;
 316 #endif /* CONFIG_ALTIVEC */
 317 #endif /* CONFIG_SMP */
 318 }
 319
 320 void flush_thread(void)
 321 {
 322         struct thread_info *t = current_thread_info();
 323
 324         if (t->flags & _TIF_ABI_PENDING)
 325                 t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT);
 326
 327 #ifndef CONFIG_SMP
 328         if (last_task_used_math == current)
 329                 last_task_used_math = NULL;
 330 #ifdef CONFIG_ALTIVEC
 331         if (last_task_used_altivec == current)
 332                 last_task_used_altivec = NULL;
 333 #endif /* CONFIG_ALTIVEC */
 334 #endif /* CONFIG_SMP */
 335 }
 336
 337 void
 338 release_thread(struct task_struct *t)
 339 {
 340 }
 341
 342
 343 /*
 344  * This gets called before we allocate a new thread and copy
 345  * the current task into it.
 346  */
 347 void prepare_to_copy(struct task_struct *tsk)
 348 {
 349         flush_fp_to_thread(current);
 350         flush_altivec_to_thread(current);
 351 }
 352
 353 /*
 354  * Copy a thread..
 355  */
 356 int
 357 copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
 358             unsigned long unused, struct task_struct *p, struct pt_regs *regs)
 359 {
 360         struct pt_regs *childregs, *kregs;
 361         extern void ret_from_fork(void);
 362         unsigned long sp = (unsigned long)p->thread_info + THREAD_SIZE;
 363
 364         /* Copy registers */
 365         sp -= sizeof(struct pt_regs);
 366         childregs = (struct pt_regs *) sp;
 367         *childregs = *regs;
 368         if ((childregs->msr & MSR_PR) == 0) {
 369                 /* for kernel thread, set stackptr in new task */
 370                 childregs->gpr[1] = sp + sizeof(struct pt_regs);
 371                 p->thread.regs = NULL;  /* no user register state */
 372                 clear_ti_thread_flag(p->thread_info, TIF_32BIT);
 373         } else {
 374                 childregs->gpr[1] = usp;
 375                 p->thread.regs = childregs;
 376                 if (clone_flags & CLONE_SETTLS) {
 377                         if (test_thread_flag(TIF_32BIT))
 378                                 childregs->gpr[2] = childregs->gpr[6];
 379                         else
 380                                 childregs->gpr[13] = childregs->gpr[6];
 381                 }
 382         }
 383         childregs->gpr[3] = 0;  /* Result from fork() */
 384         sp -= STACK_FRAME_OVERHEAD;
 385
 386         /*
 387          * The way this works is that at some point in the future
 388          * some task will call _switch to switch to the new task.
 389          * That will pop off the stack frame created below and start
 390          * the new task running at ret_from_fork.  The new task will
 391          * do some house keeping and then return from the fork or clone
 392          * system call, using the stack frame created above.
 393          */
 394         sp -= sizeof(struct pt_regs);
 395         kregs = (struct pt_regs *) sp;
 396         sp -= STACK_FRAME_OVERHEAD;
 397         p->thread.ksp = sp;
 398         if (cpu_has_feature(CPU_FTR_SLB)) {
 399                 unsigned long sp_vsid = get_kernel_vsid(sp);
 400
 401                 sp_vsid <<= SLB_VSID_SHIFT;
 402                 sp_vsid |= SLB_VSID_KERNEL;
 403                 if (cpu_has_feature(CPU_FTR_16M_PAGE))
 404                         sp_vsid |= SLB_VSID_L;
 405
 406                 p->thread.ksp_vsid = sp_vsid;
 407         }
 408
 409         /*
 410          * The PPC64 ABI makes use of a TOC to contain function
 411          * pointers.  The function (ret_from_except) is actually a pointer
 412          * to the TOC entry.  The first entry is a pointer to the actual
 413          * function.
 414          */
 415         kregs->nip = *((unsigned long *)ret_from_fork);
 416
 417         return 0;
 418 }
 419
 420 /*
 421  * Set up a thread for executing a new program
 422  */
 423 void start_thread(struct pt_regs *regs, unsigned long fdptr, unsigned long sp)
 424 {
 425         unsigned long entry, toc, load_addr = regs->gpr[2];
 426
 427         /* fdptr is a relocated pointer to the function descriptor for
 428          * the elf _start routine.  The first entry in the function
 429          * descriptor is the entry address of _start and the second
 430          * entry is the TOC value we need to use.
 431          */
 432         set_fs(USER_DS);
 433         __get_user(entry, (unsigned long __user *)fdptr);
 434         __get_user(toc, (unsigned long __user *)fdptr+1);
 435
 436         /* Check whether the e_entry function descriptor entries
 437          * need to be relocated before we can use them.
 438          */
 439         if (load_addr != 0) {
 440                 entry += load_addr;
 441                 toc   += load_addr;
 442         }
 443
 444         /*
 445          * If we exec out of a kernel thread then thread.regs will not be
 446          * set. Do it now.
 447          */
 448         if (!current->thread.regs) {
 449                 unsigned long childregs = (unsigned long)current->thread_info +
 450                                                 THREAD_SIZE;
 451                 childregs -= sizeof(struct pt_regs);
 452                 current->thread.regs = (struct pt_regs *)childregs;
 453         }
 454
 455         regs->nip = entry;
 456         regs->gpr[1] = sp;
 457         regs->gpr[2] = toc;
 458         regs->msr = MSR_USER64;
 459 #ifndef CONFIG_SMP
 460         if (last_task_used_math == current)
 461                 last_task_used_math = 0;
 462 #endif /* CONFIG_SMP */
 463         memset(current->thread.fpr, 0, sizeof(current->thread.fpr));
 464         current->thread.fpscr = 0;
 465 #ifdef CONFIG_ALTIVEC
 466 #ifndef CONFIG_SMP
 467         if (last_task_used_altivec == current)
 468                 last_task_used_altivec = 0;
 469 #endif /* CONFIG_SMP */
 470         memset(current->thread.vr, 0, sizeof(current->thread.vr));
 471         current->thread.vscr.u[0] = 0;
 472         current->thread.vscr.u[1] = 0;
 473         current->thread.vscr.u[2] = 0;
 474         current->thread.vscr.u[3] = 0x00010000; /* Java mode disabled */
 475         current->thread.vrsave = 0;
 476         current->thread.used_vr = 0;
 477 #endif /* CONFIG_ALTIVEC */
 478 }
 479 EXPORT_SYMBOL(start_thread);
 480
 481 int set_fpexc_mode(struct task_struct *tsk, unsigned int val)
 482 {
 483         struct pt_regs *regs = tsk->thread.regs;
 484
 485         if (val > PR_FP_EXC_PRECISE)
 486                 return -EINVAL;
 487         tsk->thread.fpexc_mode = __pack_fe01(val);
 488         if (regs != NULL && (regs->msr & MSR_FP) != 0)
 489                 regs->msr = (regs->msr & ~(MSR_FE0|MSR_FE1))
 490                         | tsk->thread.fpexc_mode;
 491         return 0;
 492 }
 493
 494 int get_fpexc_mode(struct task_struct *tsk, unsigned long adr)
 495 {
 496         unsigned int val;
 497
 498         val = __unpack_fe01(tsk->thread.fpexc_mode);
 499         return put_user(val, (unsigned int __user *) adr);
 500 }
 501
 502 int sys_clone(unsigned long clone_flags, unsigned long p2, unsigned long p3,
 503               unsigned long p4, unsigned long p5, unsigned long p6,
 504               struct pt_regs *regs)
 505 {
 506         unsigned long parent_tidptr = 0;
 507         unsigned long child_tidptr = 0;
 508
 509         if (p2 == 0)
 510                 p2 = regs->gpr[1];      /* stack pointer for child */
 511
 512         if (clone_flags & (CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
 513                            CLONE_CHILD_CLEARTID)) {
 514                 parent_tidptr = p3;
 515                 child_tidptr = p5;
 516                 if (test_thread_flag(TIF_32BIT)) {
 517                         parent_tidptr &= 0xffffffff;
 518                         child_tidptr &= 0xffffffff;
 519                 }
 520         }
 521
 522         return do_fork(clone_flags, p2, regs, 0,
 523                     (int __user *)parent_tidptr, (int __user *)child_tidptr);
 524 }
 525
 526 int sys_fork(unsigned long p1, unsigned long p2, unsigned long p3,
 527              unsigned long p4, unsigned long p5, unsigned long p6,
 528              struct pt_regs *regs)
 529 {
 530         return do_fork(SIGCHLD, regs->gpr[1], regs, 0, NULL, NULL);
 531 }
 532
 533 int sys_vfork(unsigned long p1, unsigned long p2, unsigned long p3,
 534               unsigned long p4, unsigned long p5, unsigned long p6,
 535               struct pt_regs *regs)
 536 {
 537         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs->gpr[1], regs, 0,
 538                     NULL, NULL);
 539 }
 540
 541 int sys_execve(unsigned long a0, unsigned long a1, unsigned long a2,
 542                unsigned long a3, unsigned long a4, unsigned long a5,
 543                struct pt_regs *regs)
 544 {
 545         int error;
 546         char * filename;
 547
 548         filename = getname((char __user *) a0);
 549         error = PTR_ERR(filename);
 550         if (IS_ERR(filename))
 551                 goto out;
 552         flush_fp_to_thread(current);
 553         flush_altivec_to_thread(current);
 554         error = do_execve(filename, (char __user * __user *) a1,
 555                                     (char __user * __user *) a2, regs);
 556
 557         if (error == 0) {
 558                 task_lock(current);
 559                 current->ptrace &= ~PT_DTRACE;
 560                 task_unlock(current);
 561         }
 562         putname(filename);
 563
 564 out:
 565         return error;
 566 }
 567
 568 static int kstack_depth_to_print = 64;
 569
 570 static int validate_sp(unsigned long sp, struct task_struct *p,
 571                        unsigned long nbytes)
 572 {
 573         unsigned long stack_page = (unsigned long)p->thread_info;
 574
 575         if (sp >= stack_page + sizeof(struct thread_struct)
 576             && sp <= stack_page + THREAD_SIZE - nbytes)
 577                 return 1;
 578
 579 #ifdef CONFIG_IRQSTACKS
 580         stack_page = (unsigned long) hardirq_ctx[task_cpu(p)];
 581         if (sp >= stack_page + sizeof(struct thread_struct)
 582             && sp <= stack_page + THREAD_SIZE - nbytes)
 583                 return 1;
 584
 585         stack_page = (unsigned long) softirq_ctx[task_cpu(p)];
 586         if (sp >= stack_page + sizeof(struct thread_struct)
 587             && sp <= stack_page + THREAD_SIZE - nbytes)
 588                 return 1;
 589 #endif
 590
 591         return 0;
 592 }
 593
 594 unsigned long get_wchan(struct task_struct *p)
 595 {
 596         unsigned long ip, sp;
 597         int count = 0;
 598
 599         if (!p || p == current || p->state == TASK_RUNNING)
 600                 return 0;
 601
 602         sp = p->thread.ksp;
 603         if (!validate_sp(sp, p, 112))
 604                 return 0;
 605
 606         do {
 607                 sp = *(unsigned long *)sp;
 608                 if (!validate_sp(sp, p, 112))
 609                         return 0;
 610                 if (count > 0) {
 611                         ip = *(unsigned long *)(sp + 16);
 612                         if (!in_sched_functions(ip))
 613                                 return ip;
 614                 }
 615         } while (count++ < 16);
 616         return 0;
 617 }
 618 EXPORT_SYMBOL(get_wchan);
 619
 620 void show_stack(struct task_struct *p, unsigned long *_sp)
 621 {
 622         unsigned long ip, newsp, lr;
 623         int count = 0;
 624         unsigned long sp = (unsigned long)_sp;
 625         int firstframe = 1;
 626
 627         if (sp == 0) {
 628                 if (p) {
 629                         sp = p->thread.ksp;
 630                 } else {
 631                         sp = __get_SP();
 632                         p = current;
 633                 }
 634         }
 635
 636         lr = 0;
 637         printk("Call Trace:\n");
 638         do {
 639                 if (!validate_sp(sp, p, 112))
 640                         return;
 641
 642                 _sp = (unsigned long *) sp;
 643                 newsp = _sp[0];
 644                 ip = _sp[2];
 645                 if (!firstframe || ip != lr) {
 646                         printk("[%016lx] [%016lx] ", sp, ip);
 647                         print_symbol("%s", ip);
 648                         if (firstframe)
 649                                 printk(" (unreliable)");
 650                         printk("\n");
 651                 }
 652                 firstframe = 0;
 653
 654                 /*
 655                  * See if this is an exception frame.
 656                  * We look for the "regshere" marker in the current frame.
 657                  */
 658                 if (validate_sp(sp, p, sizeof(struct pt_regs) + 400)
 659                     && _sp[12] == 0x7265677368657265ul) {
 660                         struct pt_regs *regs = (struct pt_regs *)
 661                                 (sp + STACK_FRAME_OVERHEAD);
 662                         printk("--- Exception: %lx", regs->trap);
 663                         print_symbol(" at %s\n", regs->nip);
 664                         lr = regs->link;
 665                         print_symbol("    LR = %s\n", lr);
 666                         firstframe = 1;
 667                 }
 668
 669                 sp = newsp;
 670         } while (count++ < kstack_depth_to_print);
 671 }
 672
 673 void dump_stack(void)
 674 {
 675         show_stack(current, (unsigned long *)__get_SP());
 676 }
 677 EXPORT_SYMBOL(dump_stack);